One note from me: * I didn't notice on the schematics it did show which other 2 chips make up that bit. It initially only shows 2K of RAM chips, but the bottom it shows which other two chips are on the same bit. I should have swapped 4 chips looking for the bad one. Luckily I got there in the end.
LOVE your SwTPC (SwatPuck) series. I have one of these - home-built. It is in storage. For replacing bad 21L02 memory chips - go to Electronic Goldmine and search for 21L02. They have a 'new old stock' of TI chips for about $7.00 each. I also have original documentation - in a notebook. Schematics on most of the boards. I built my SwTPC when I was about 21 or 22 yrs old - didn't know what I was doing. Bought the bare boards and the parts. I think I socketed everything. Miraculously, the computer powered up with very few issues. I had to add a 0.33uF capacitor on the +5V regulator on the main board - it was oscillating. I had 2kRAM - and had to expand it to 4kRAM so I could run Tom Pitman's Tiny BASIC - that came on punch tape. I had an ASR33 teletype. (It took about 5 minutes to load) I originally started out with the Video board that SwTPC offered. I also soldered that one together and got it to work - providing video to a 9" SONY TV that I soldered a wire into and fed the video into. (You could switch the TV to a blank channel on the dial.) The keyboard I used was a kit that Radio Shack sold for a brief time. I assembled it and wired a cable from it to the input of the video board... or was it to a plug-in card on the SwTPC? IT's been a while ago... I don't remember. The computer boards - I fabricated my own housing for them from plywood - it was about 24" x 24" square and 10 - 12-inches tall. I designed my own power supply - probably not acceptable by todays standards - and barely acceptable back then, but it worked. I never got any floppy or hard drive storage, and only used paper tape for my storage. When I finally upgraded my computer, I went with a VIC-20 which had as much memory (RAM) as my SwTPC but also had color and other features that I could not get on my SwTPC - like cassette program storage. I'm sure that there are others here who can help, but if you need any details on your 6800 SwTPC, feel free to contact me. I'm on LinkedIn.
Hi Adrian. Your part 2 is still showing that part 3 is coming soon. Btw I'm loving this series and trying to guess / diagnose the fault before it's revealed. Great fun.
Hi Adrian, I’m from Germany and watch you channel basically for the Commodore Stuff. I really like it. But now to SWTPC, in the 80/90 th. I worked a Lott with this heavy Systems. The where used for logistics in Pharmacy/Drug Stores here in Germany. And the company I worked for also wrote some Software for accounting and billing. Usually first we used double 8` floppy disk drives and later also 5 to 10 MByte Harddrives. There where tripple density controller for the Floppy Drives wit a capacity of 3,4 MByte, which was amazing for this time. I really like this SWTPC Videos, great job 👍
Back in the late 70's, I used a Motorola 6800 D2 evaluation kit to programme a complete radio paging system in machine code. The data storage was with a cassette tape, for which I used my own cassette recorder. I had to build an EPROM programmer from scratch to programme 2708 EPROMs with the paging code. They were 1k byte with three power rails, and needed multiple passes in order to programme each cell. The programmers were really expensive to buy back then. I still remember the weird ozone smell from the home built UV EPROM eraser. The radio paging controller we made had a 7 segment LED display and a keypad. It connected to the paging transmitter and could control up to 1000 pagers on the system. Its code fitted into a single 2708 EPROM with space left over. The computer you are working with I would have given my eye teeth to have then. Life would have been so much easier. Calculating branch offsets manually was quite a challenge, and testing the code was extremely time consuming. I really enjoy your channel, Adrian. So many wonderful memories.
The 21L02 chip is used as video memory on the TRS-80 Model I. The Model I only provided 7 bits of video memory. We had t piggyback the 8th chip and do some minor mods to the board to enable the 8th bit and with that, lowercase.
@@adamw.8579 I did some reverse engineering on a couple of 8051 based control systems lately, and to be honest, all of them used external RAM as well (not saying that every 8051 based design out there does, just all of the ones I happened to come across). One of them apparently had the C compiler used to create the program even setup in a way that everything that was not stack, register or memory mapped IO reside in the external RAM. Even stuff like loop variables, which I thought was quite inefficient. And it even had 128k of external RAM that it did access via bank switching, using an I/O line as address line 16.
As I understand it systems like the Atari 2600 and 8501 could do so much because the code could be read from ROM (or flash in the case of more modern microcontrollers). If both code and data needed to share 128 bytes, I seriously doubt you could do much. 128 instructions is really not a lot, and that's the absolute best-case scenario: all opcodes, no operands and no data or variables.
@@andrewsprojectsinnovations6352 8051 is a Harvard architecture - separate code and data spaces. Usually 2-8kB code ROM/FLASH max.64kB, and internal 128 bytes RAM, additional RAM may be installed with cost port 0 and 2 used as address/data multiplexed bus for external ram up to 64kB. Some simple units - for example intelligent peripheral use all ports and only internal 128bytes of ram or 256 in version 8052.
Nice! I wrote an emulator for it, also for Motorola Exorciser (search for "exorsim"). Your FPGA should connect to a real floppy drive :-) Recently I want to make a cassette tape interface like the SWTPC AC-30, but higher baud, more modern modulation.
Visited the Computer History Museum in Silicon Valley yesterday and was low-key excited to see that they have a SWTPC 6800 on display in their section on early personal computers.
Great description and tour of the various memory test programs. I never had the patience for them where the RAM was socketed.. the video card on my digital group system uses 2102s so I'd just swap chips from the 6800 to that and if I saw corrupted video I knew I had bad ones. Once I had those vetted I worked from there. I feel so lazy now.
These early computers required machine level understanding like Adrian has. An obvious opportunity for development to more accessible higher level languages.
I used to run quite powerful IBM RS/6000 machines connected to the serial when I worked at IBM. Lots of those machines did not even have a graphics board in their config.
Very interesting way of troubleshooting, using the provided diagnostic tests as the "keyhole" into the system, and sure a great find to point ot the one bad chip. When it comes to video length, I wouldn't even mind a day-long video. I know, this is not at all feasible, but watching you troubleshoot this retro stuff is just something I will never get tired of. ;-)
Loved this video Adrian: the diagnostic, the mental process followed, the different hypothesis tested, all of that topped with your own vast personal experience and as always your very engaging storytelling and explanation of everything you are doing. YOU ROCK Adrian, thank you, thank you, thank you!
I know someone who, when they were 12 years old, got a mouse. His dad called them to see if there was a device driver to go with it and the response was that if his 12-year-old didn't know how to write a device driver for it then he didn't deserve to have a mouse. Ah, happy times. I do miss having schematics for electronic devices though. The control circuitry for my coffee maker failed the other day which was no big deal because I wanted to control it via networking, 12V and an inverter anyway but the company wouldn't even tell me what the wires were because "it would invalidate my [non-existent] warranty" and "for safety reasons".
That's why I tend to use very old electronics stuff. I can get schematics, and I can repair it. No amount of 'new' and piles of sophisticated features is of value if something doesn't actually work and can't be fixed.
Reminds me of a certain type of Linux head who insists you compile everything and somehow know not to accept the default compiler flags for 1 in every 12 package..!
@@ImpetuouslyInsane Yes but I wouldn't touch Apple's overpriced, underspeced and locked down products with a 10' pole. No prizes for guessing my OS of choice!
Really enjoying this series. My computing history starts with the VIC-20 and Apple II+ so I have virtually no exposure to something like this. I like to be able to appreciate what the people before us had to go through to enjoy the hobby or process actual work at a company. If you ever run out of things to fix (haha, I know) I'd be fascinated to see what you could do with late 70s early 80s arcade game PCBs. There's lots of variety there as, especially early on, the boards were basically single purpose computers made for just playing that one game. The concept of "cartridges" or something similar didn't show up until maybe Sente in the early/mid 80s as far as I know.
Way back then I built a Z80 system from magazine plans. The 4K RAM card used 2102s.(1Kx1) I designed a new version using 2114 chips (1Kx4). I keep thinking about digging it out and doing an "anachronistic restoration" on it by pulling both boards and adding one of those 32Kx8 CMOS RAMS to the Eprom card.
Not only does that centralized clock save on chips, it also ensures the various clocks will be in sync between all carts, something you can't really do when every cart has its own clock.
True - and with the really moderate clock speeds of the era, you don't need to worry about adverse effects that the long connections between clock generator and clock user may cause, or even getting out of phase because the connections differ in length. With today's speeds, such an approach would be much harder to implement.
@@Colaholiker Another nice thing is, that with the 6800 bus you can easily share the bus between two masters. The CPU is only accessing when this clock is high, so the bus is free when its low. Was for example extensively used for graphics which accessed the shared memory in between the CPU cycles.
I owned a Color Computer which was great. It had a bunch of great business software and also a cartridge called EdTasm which is a 6800 assembly language editor/assembler. This is what I learned assembly language on. In fact, a company that I was involved in used the CoCo motherboard to make engine test systems for Cummins diesel engines at the 20 acre plant near Jamestown, NY. Worked great and really reliable.
This is a pretty interesting repair. I've got a breadboard Z80 project that's similar in a lot of ways. I got a kick out of part 2 on the serial stuff bcz I knew exactly where that was headed as a oldster telecom engineer.
oooh! this was cool! I started using computers only in 1982 -- pretty much when the speccy came out, and it's _so_ cool to learn about computers before that!
Just remember that computers far more advanced than the ZX (or VIC) line existed before this machine was built. (The Xerox Alto of 1972 for instance, which became the inspiration for both Apple Lisa/Mac, M$ Windows and most graphical UNIX shells of the 1980s.)
If you think about it, in some ways computing has returned to this early structure with the popularity of credit card sized computers such as the Raspberry Pi and Arduino. The biggest difference is the also include a mass storage system in their tiny form factor. It requires an external terminal to access just like these old computers. They are mean to be interfaced to the real world through GPIO.
I have enjoyed seeing your process and this very old computer come back to life. I hope you can come up with a replacement for the bad chip - it would be great to see the machine maxed in memory.
This video took me back to my first real job. The company had a Cromemco 8", dual floppy system that was only a bit more capable than this SWTPC. It was primitive, but at the time, it was state of the art, and I loved using it.
I worked for Motorola Micro Systems when all the 6800 family was new as a bench technician. When we would work on memory boards. We wrote a script that would write 3's and c's to memory. Then just watch the address line cycles. Easy to figure out what was not working. I wrote a bunch of scripts for trouble shooting. I wish i still had copies. Motorola sold memory boards for $1 a byte. So a 16k memory board cost $16,000. When the 6809 came out it had better memory management, with paged memory and we came out with 32k and 64k memory boards. The 6800 memory map was flat. You can put what card at what ever address you wanted with a few exceptions. The stack was down at the bottom of memory, and the mbug.resided at the top. When 9600 baud came out we were amazed at how fast it was. We used either a Motorola terminal or a TI thermal printer. I have been looking for a Motorola Exorsiser or a SWTP computer years. There was a Basic that came.on proms. I think it was called tiny basic. I might have a set of eeproms laying around.that that i will send to you if want them. We dold a card ths5 lot of fun working on new technology. Back in the the 70. There is a trick that we would use to watch address lines. I would ground one pin and all of the address lines would start toggling. I loved those computers easy to program easy to learn to use. I think all the software that would run on an Exorciser would run on a SWTP computer.
I used to maintain a pair of Metrodata character generator that Exorcisor based. They were scrapped about two years after I left the company. Each had 6 NTSC video cards. I was told that they were given to the remaining Metrodata engineer, because the company had closed down. It also had a SMS 8" floppy disk system.for one of the computers. Dual drives and it weighed about 120 pounds. They were replaced with a bunch of Commodor 64 computers, and one 1541 drive. along with an EPG decoder/character generator to replace the local program guide. It was uplinked on a subcarrier on our WGN uplink. The early Weather Channel interface was 6502 based. The ICs were almost a match to a VIC20. I think that I still have a Vector Electronics protoboard for the Exorcisor bus.
I'm working on a heavily corroded board from a 60's camera. Heated 50% dilute Pine-Sol can do wonders. I use an ultrasonic cleaner with heater, but just hot soaking will shine up connections & boards well. It may remove weak solder mask though. But at that era, some boards don't even have it!
Good work on this one, I didn't even scream at the screen once! I did, however, pause to download those tests and take a quick look at them before you started them up. The best memory test that I actually implemented at work was a rotating series of "100" and "011". Three doesn't divide into eight, so it really gives the memory a good shakedown. I got the idea from the old Mac Plus startup memory test where you could visibly see the pattern on the screen. It's probably the best _simple_ memory test there is. It actually caught problems in some obscure boards we got from Intel! (this was in early 2001)
I'd love to see a breakdown of what those memory test programs are actually doing. It seems amazing that so few instructions are actually testing the memory in the machine! Loving this series, as it is from the era just before I started using computers (my first was a Commodore 64), so it's fascinating to see. This particular machine seems to be remarkably elegant, although I'm not familiar enough with its contemporaries to know how special the SWTPC is.
When I see that computer I still think of my friend Judy, who had one. Thanks for working on it. Not as fancy as OS9, but my friend used to run FLEX this: en.wikipedia.org/wiki/FLEX_(operating_system) Images/Docs: www.simonwynn.com/flex Looking at the hardware on the computer, and at risk of seeming like shill, I am reminded that Evaporust really would take that rust off pretty well. I used it on a tray of assorted hardware. It may remove black oxide, but for hardware with other kinds of plating, such as zinc-chomate, it seemed to leave it intact, while doing a pretty good job. Afterwards the hardware could be sprayed with something to protect the rust--or perhaps a thin coat of lacquer would also protect it, as long as it's sprayed outside with proper breathing protection. I prefer lacquer because it dries harder and in a shorter time. I run the remainder back through a funnel and a coffee filter--before putting it back into the container. Although Evaporust is safe, like vinegar, it's PH means that it's not good to get into cuts. I think that Rustoleum also has their own chelating rust-remover too, that might have greater availability. Also, I had an experimental idea: cleaning boards in an ultrasonic cleaner, but with a twist, of using some Kool Mist mixture to prevent corrosion whilst cleaning. It should prevent rust from forming. Kool Mist is a fairly safe chemical that can be added to distilled/dionized water that allows steel and iron to be soaked in it to prevent rusting. It's mixed about an ounce to a quart. After cleaning, the board could be blown out with either compressed air--or small handheld leaf-blower.
Several suggestions here as to better ways to approach the problem but what you did replicated the efforts of hobbyists when this computer was new using the tools they had available. There was no laptop just a dumb terminal and each test was loaded via audio cassette (a real toss of the dice each time you hit play!). This video would have represented hours of effort but that was the hobby at the time. Adrian, even your unfamiliarity with the system is reminiscent of that of the original owner!
Several hours into this series, I've come to the conclusion that this machine is a step too far for me. Good on your enthusiasm, though, and I hope you enjoy finishing it! 👍
TeraTerm allows you to directly send files (just drag&drop the whole file into the Terminal window), so you don't need to copy/paste from the file manually. i use that myself to load .bin files via serial onto my 65C02 SBC and it works great
Thank you Adrian! This brings back so may good memories (no pun intended). I've used the same tools many times in the past. I actually ended up modding them to prompt for start and stop addresses. The BADDR routine in the MIKBUG ROM can be used for this. Looking forward to your next SWTPC video!
@36:12 I'm sure you are aware of it, but I think it is important to state it explicitly: You can get false *positive* readings (i.e. "is OK" when the RAM still has issues), but you can *not* get false negative readings. If the memory test claims that "memory is broken", *something* in your computer, likely the memory, acutally is broken. PC component vendors like to claim otherwise if they don't trust your memory test and try to reject returns due to the test being "incompatible" or reporting a false reading. For example, the German computer magazine c't reported about low-quality SDRAM modules around 1999 and people started testing their RAM with extensive tests. There was a notable backlash against the c't report because some vendors were unhappy with the increased amount of "your PC has bad RAM" claim. In one of the follow-up issues, they published one or two letters to the editors by upset vendors.
Thanks for the SWTPc videos. I built one back in college which I still have. I has some spare 21L02 chips from way-back-when. Let me know if you need one to fix that board as I think that they are a little hard to find.
Thank you! I really enjoyed this. Love the troubleshooting. It is interesting how viewers lose interest on longer videos. I've seen this with my antique refrigeration repair videos as well. This computer is really cool... just never seen anything like it!
Wow! I haven't heard of SWTP in decades. If RAM appears bad I first reseat all socketed IC's, (machined-pin sockets are the only ones I trust,) then I look for power supply voltages on a couple of chips, then I look for clocks and refresh, then I use my laser thermometer and look for hot chips. If I find nothing, only then do I bother with RAM diags. It's quicker to do the other tests first, and RAM tests back then weren't very sophisticated. If I saw a bunch of errors I'd try to identify a hung address decoder bit or I/O buffers. Socketed chips make fixing RAM boards a breeze, slow but a breeze. Fortunately, I have a pretty good stock of old LSI and VLSI support chips to swap them in and out. If the fault is intermittent then a point-source heatgun and freeze mist are in order. What chip is used for mem on that board? I'l look to see if I have a couple I can send you. The best person to fix antique boards is an antique tech, and I'm in my 70's. :)
Another great video! Maybe consider doing an extended version (part 2) of some of your videos for Patreon Patrons for those of us who like the long-format? An Adrian "After-Party" if you will?
With the ZX Spectrum being 40 years old today, in celebration I powered my childhood machine up for the first time in decades and am going through similar issues. Got it booting after replacing a RAM IC whose data pin was jamming the bus but now have more intermittent issues to look at (another IC dragging down the bus). All good fun!
Pardon me for being a semantic nerd, but bootstrapping is the process of loading a small program that in turn is able to load the main system into RAM. ROM based computers like the ZX line and most other home machines didn't have to do that, at all. They just started, instantly.
@@herrbonk3635 Very true. I (mis)used the word “boot” to indicate that the machine successfully executed ROM code to the extent that the Sinclair copyright message appears and is accepting commands that let me try load software :)
@@graemedavidson499 Or commands that builds a program. It wasn't really intended as a game computer after all (despite the fantastic teletext style colours :D) My point was that the BASIC interpreter in ROM *_is_* the (operating) system. Loading external software is another thing, and similar to computers that does indeed "boot".
Modern computers are easier when they work, but the one I just built has gremlins. Newer hardware pushes itself so hard it's always on the edge of failure at stock clocks, but because it's consumer grade, reliability isn't a concern. Nothing adequately diagnoses itself. When something fails and you don't know which part, just buy new stuff until it works. The industry likes it that way.
@Adrian's Digital Basement If you don't have memory location info on the schematics then you can use one of the faulty chips to "map" which socket is what memory range. Use a known bad chip and swap it into each other known working socket and run the test.
That was interesting. Like to see you find a replacement for the chip. I remember my uncle working on this type of computer. And it seemed so hard to me back then for me to understand. When I was very young. Now I have worked on much harder things it does not. Just very simple. Still is hard for most people though. :P
I have one of those Motorola development boards MEK6800D2. It's similar to a KIM, but with a second board with a LED display and hefty keypad for input.
The big difference between modern computers and ones like these is the fact you can actually dive deep into repairs, I used to repair "modern" (mostly late 90s to late 2000s) comptuers as a job, and the transition from repairable at component level to the "replace the everything" that has become the norm now was a really fast process, and it's what put me off repairing computers, they just build the parts to be used and binned, rather than maintained for life like this old beast...
I think that transition happened around the time when chips stopped failing as often, and when they did, it took a hot air rework station to replace a minimum 164 pin flat pack. ;-) It takes a pretty hard-core repair person to trek into BGA territory. “Replace the everything” is the only valid option at scale.
@@michaelterrell Great. Are you trying to say you would _want_ to replace flat packs and BGA ICs for a living, with a soldering iron? Lots of things _can_ be done. That doesn't mean it makes economical sense.
@@nickwallette6201 We didn't use any BGA chips, but I did change or completely resolder a lot of SMD ICs from six to 288 pins at work.. I could send them to rework, and wait. And wait. And wait some more. They intentionally hid about $7,000 worth of new boards, instead of doing the rework. and I was accused f losing or stealing them. I dug through everything at the rework area, and found every one of them in front of their boss. After that, I rarely sent anything to rework. I could do the work right then, without taking it off my bench. I had one of the later B&L StereoZoom microscopes on a cart with proper ESD protection. I had three Edsyn Loner soldering irons. Two with the smallest standard chisel tips, and a third with a 0.015" tip along with 0.015" Ersin rework solder. I did better work than the three women in Rework, and I did it faster. I also worked with Manufacturing Engineering to update our entire reflow soldering process. It was stuck in the 1206 era, and we had just introduced 0201 components. By doing my own rework, I was more than twice as productive when compared to anyone at the board/module level. I also built test fixtures, and updated test procedures. A lot of this was brought on by the ISO9001 certification process. Some cards had well over a dozen versions, with a six page test data sheet. The outside 'expert' saw nothing wrong with the existing procedures, but having to pint out over seven pages and marking every line on all but six as N/A wasted a lot of paper and time. I also took the average test time for that group of boards from 7.5 hours down to 17 minute average with the new fixture and test procedure. It had 16 Sallen-Key filters for easy selection of the video output bandwidths. They were identical, in two frequency ranges. The output frequency was set with two pairs of precision resistors. Slight variations in the inter element capacitance within the circuit board required some Select In Test. One of these went to the ISS as part of a kU band Data, Voice and Video uplink. I worked on about half the boards in that receiver, both digital, analog and RF. I'm nnot a hobbyist, I'm a retired Broadcast engineer, and I did mission critical work at remote sites with zero outside support. I did Engineering Tech work at that last job. I tested one off products. I certified new suppliers and I did failure analysis.
@@michaelterrell That's impressive. Still.. I think even you would agree that's probably not a normal situation. Right? We're really losing the thread here. There's a lot said about how today's electronics are "disposable" and "we used to be able to work on them" as if a through-hole Ryzen were a possibility. I'm just saying ... when you can walk into a store and buy a brand new Blu-ray player for $50, trying to get a DRAM IC off the board and replaced with another is just not economical. Same goes for replacing an Ethernet controller on a $150 motherboard. As these things get more tightly integrated, and thus more specialized, and more difficult to work on, the tools required to test and repair them get more precise, expensive, and only attainable to a more highly-trained specialized workforce with -- frankly -- better things to do with their time. So the repair industry dries up, and there's nobody left to sell schematics and test jigs to. So you could surgically implant a Bluetooth transceiver onto a tick's butt. Great. But are you going to do that at an hourly rate that makes it preferable to bring my sub-$100 device to you, rather than ordering a new one with free 1-day delivery? That's my point, bud. The skills exist, but within a smaller pool of people who have spent more time honing their craft, and have way cooler toys, and aren't willing to contract out for peanuts anymore. Is that not true?
Oh! Those are Patreon names scrolling up the screen... I though my new monitor had a 60hz hum bar on the left side. Good to know. Maybe a slow "bottom ticker tape roll" would work better? And no, my name isn't there yet, sadly :O\ Thank you for the video. Very COoL kit'ness. You RoCk!
I love older computers. I hope to see more. Right now I'm trying to get my hands on 2 or 3 special systems. compupro 8/16. And hopefully post a video. But trying to find someone that would be willing to donate one is impossible....
Apparently the guy who founded Smoke Signal Broadcasting was a program director for CBS Radio in Hollywood. They later made 68K UNIX systems but they sold very poorly.
20:08 "Computers are simpler now...." - Well, they are when they work, but the average user has no chance if they stop. A tinkerer could figure out a hardware fault by swapping boards in a desktop pc, but if Windows decides not to play, it's a whole different ball game. Tracing bad RAM chips on a board is child's play in comparison.
i recently saw a double floppy disk unit of the swtpc in the exact same design and case (would guess it was 2 8 inch side by side). it was just one picture on the internet, sadly i forgot the URL. Still thought might be worth mentioning
I just remembered this little tide bit if you are programming the 6820, paralllel chip there was a bug that caused data corruption. The bug was fixed when 6821 came out. For the 6820 you had to do a reset before writing to a register.
IIRC someone (SSB maybe) offered a video card for the SWTP 6800 computer, but it wouldn't have worked with the MicBug monitor, however there were latter versions of that rom offered.
Now I wonder, while doing the troubleshooting in this way, using the tools that were available back in the day is an experience of its own, since all the chips were socketed, couldn't you just run all of them through the Retro Chip Tester?
With the 2102 RAM chip being a 1K x 1 device, you actually have 3 banks of 1K bytes of RAM. By jockeying the bad chip around to the highest location (7C00 hex) you could have used the board as a 3K byte board.
They made their own 6800 system called the Chieftain which was fully compatible with the SWTPc 6800. And I believe it was available with a built-in Shugart SA400 floppy drive and DOS68.
Good on you for respecting your viewer's time. My threshold is around an hour. There are live streams that I don't watch (live or after the fact) because they are way too long at two or three hours. And those are not jammed pack, as they have filler.
As much as I would enjoy a very long version of this series, you are very right as a video that long would end up in my "I want to watch this when I have time" pile. Guess what? That turns into the "I never got to it" pile.
I'm surprised you don't have any 2102s in your collection. As I recall ,those were the most common RAM chip in computers of this era, before the 41xx series DRAM chips came to dominate with their higher capacities.
@@robertdixon8238 Thank you. :) (Also, I'm facepalming a little at my own stupidity to have not caught on to the obvious M6800-M680000 connection, because I kind of knew that about the M68k.)
I would have just pressed down on each chip to start with you tend to find with time they magically work there way out of there sockets. If that didn't work then I would have popped each one out and refitted. I don't think I have ever need to use dexoit. Anyway great to see an old machine coming to life.
Adrian, Love your vids. Please get a spray can lid and cover that capacitor. Every time you held a board over it with your hand under it, I was having palpitations.
I love these old machines. With all the chips on the memory board in sockets I'm surprised you didn't test them all. I don't know if it would have saved time or not.
This is badly making me want to start working on my CompuPro 8/16 S-100 system again. I think the only ROMs in my system are for floppy booting, I wonder if there are some diagnostic ROMs out there I could find?
I have a an TRS-80 model 1 and it has video memory issues and I was wondering if I could stack the chips to fix the video issues. I don't have the skills or knowledge that you have to figure out which chip(s) is bad. Would stacking fix it? Thanks and keep the videos rolling.
One note from me:
* I didn't notice on the schematics it did show which other 2 chips make up that bit. It initially only shows 2K of RAM chips, but the bottom it shows which other two chips are on the same bit. I should have swapped 4 chips looking for the bad one. Luckily I got there in the end.
OK this one time, but don't let it happen again.
How did you not hear me shouting that at my computer?
LOVE your SwTPC (SwatPuck) series. I have one of these - home-built. It is in storage.
For replacing bad 21L02 memory chips - go to Electronic Goldmine and search for 21L02. They have a 'new old stock' of TI chips for about $7.00 each.
I also have original documentation - in a notebook. Schematics on most of the boards.
I built my SwTPC when I was about 21 or 22 yrs old - didn't know what I was doing. Bought the bare boards and the parts. I think I socketed everything. Miraculously, the computer powered up with very few issues. I had to add a 0.33uF capacitor on the +5V regulator on the main board - it was oscillating.
I had 2kRAM - and had to expand it to 4kRAM so I could run Tom Pitman's Tiny BASIC - that came on punch tape. I had an ASR33 teletype. (It took about 5 minutes to load)
I originally started out with the Video board that SwTPC offered. I also soldered that one together and got it to work - providing video to a 9" SONY TV that I soldered a wire into and fed the video into. (You could switch the TV to a blank channel on the dial.)
The keyboard I used was a kit that Radio Shack sold for a brief time. I assembled it and wired a cable from it to the input of the video board... or was it to a plug-in card on the SwTPC? IT's been a while ago... I don't remember.
The computer boards - I fabricated my own housing for them from plywood - it was about 24" x 24" square and 10 - 12-inches tall.
I designed my own power supply - probably not acceptable by todays standards - and barely acceptable back then, but it worked.
I never got any floppy or hard drive storage, and only used paper tape for my storage.
When I finally upgraded my computer, I went with a VIC-20 which had as much memory (RAM) as my SwTPC but also had color and other features that I could not get on my SwTPC - like cassette program storage.
I'm sure that there are others here who can help, but if you need any details on your 6800 SwTPC, feel free to contact me. I'm on LinkedIn.
Hi Adrian. Your part 2 is still showing that part 3 is coming soon. Btw I'm loving this series and trying to guess / diagnose the fault before it's revealed. Great fun.
Hi Adrian, I’m from Germany and watch you channel basically for the Commodore Stuff. I really like it. But now to SWTPC, in the 80/90 th. I worked a Lott with this heavy Systems. The where used for logistics in Pharmacy/Drug Stores here in Germany. And the company I worked for also wrote some Software for accounting and billing. Usually first we used double 8` floppy disk drives and later also 5 to 10 MByte Harddrives. There where tripple density controller for the Floppy Drives wit a capacity of 3,4 MByte, which was amazing for this time. I really like this SWTPC Videos, great job 👍
Back in the late 70's, I used a Motorola 6800 D2 evaluation kit to programme a complete radio paging system in machine code. The data storage was with a cassette tape, for which I used my own cassette recorder. I had to build an EPROM programmer from scratch to programme 2708 EPROMs with the paging code. They were 1k byte with three power rails, and needed multiple passes in order to programme each cell. The programmers were really expensive to buy back then. I still remember the weird ozone smell from the home built UV EPROM eraser.
The radio paging controller we made had a 7 segment LED display and a keypad. It connected to the paging transmitter and could control up to 1000 pagers on the system. Its code fitted into a single 2708 EPROM with space left over.
The computer you are working with I would have given my eye teeth to have then. Life would have been so much easier. Calculating branch offsets manually was quite a challenge, and testing the code was extremely time consuming.
I really enjoy your channel, Adrian. So many wonderful memories.
The 21L02 chip is used as video memory on the TRS-80 Model I. The Model I only provided 7 bits of video memory. We had t piggyback the 8th chip and do some minor mods to the board to enable the 8th bit and with that, lowercase.
Adrian: 128 bytes not enough RAM to do anything serious
Atari 2600: I disagree.
8051 MCUs also disagree. Many industrial control units use this one to this day.
@@adamw.8579 I did some reverse engineering on a couple of 8051 based control systems lately, and to be honest, all of them used external RAM as well (not saying that every 8051 based design out there does, just all of the ones I happened to come across). One of them apparently had the C compiler used to create the program even setup in a way that everything that was not stack, register or memory mapped IO reside in the external RAM. Even stuff like loop variables, which I thought was quite inefficient. And it even had 128k of external RAM that it did access via bank switching, using an I/O line as address line 16.
As I understand it systems like the Atari 2600 and 8501 could do so much because the code could be read from ROM (or flash in the case of more modern microcontrollers). If both code and data needed to share 128 bytes, I seriously doubt you could do much. 128 instructions is really not a lot, and that's the absolute best-case scenario: all opcodes, no operands and no data or variables.
@@andrewsprojectsinnovations6352 8051 is a Harvard architecture - separate code and data spaces. Usually 2-8kB code ROM/FLASH max.64kB, and internal 128 bytes RAM, additional RAM may be installed with cost port 0 and 2 used as address/data multiplexed bus for external ram up to 64kB. Some simple units - for example intelligent peripheral use all ports and only internal 128bytes of ram or 256 in version 8052.
PICs also disagree.
Nice work. As a coincidence, I'm working on an FPGA recreation of this system at this very moment.
Nice! I wrote an emulator for it, also for Motorola Exorciser (search for "exorsim"). Your FPGA should connect to a real floppy drive :-) Recently I want to make a cassette tape interface like the SWTPC AC-30, but higher baud, more modern modulation.
@JENNITA B.O Be-gone bot!!
@@jhallenworld The FPGA card has an SD card so I can do stuff on that if I take it that far.
@@NathanChisholm041 Report, don't respond.
Visited the Computer History Museum in Silicon Valley yesterday and was low-key excited to see that they have a SWTPC 6800 on display in their section on early personal computers.
Great description and tour of the various memory test programs. I never had the patience for them where the RAM was socketed.. the video card on my digital group system uses 2102s so I'd just swap chips from the 6800 to that and if I saw corrupted video I knew I had bad ones. Once I had those vetted I worked from there. I feel so lazy now.
Thank You for making this videos for us, I truly enjoy watching You tinker and repair all this good stuff. As always, great video!
I really enjoyed watching you troubleshoot this machine. I would love to see it do some practical work.
These early computers required machine level understanding like Adrian has. An obvious opportunity for development to more accessible higher level languages.
I used to run quite powerful IBM RS/6000 machines connected to the serial when I worked at IBM. Lots of those machines did not even have a graphics board in their config.
Very interesting way of troubleshooting, using the provided diagnostic tests as the "keyhole" into the system, and sure a great find to point ot the one bad chip.
When it comes to video length, I wouldn't even mind a day-long video. I know, this is not at all feasible, but watching you troubleshoot this retro stuff is just something I will never get tired of. ;-)
Loved this video Adrian: the diagnostic, the mental process followed, the different hypothesis tested, all of that topped with your own vast personal experience and as always your very engaging storytelling and explanation of everything you are doing. YOU ROCK Adrian, thank you, thank you, thank you!
*Adrian
@@Plarndude thank you and corrected! I don’t know how I missed the misspelling of Adrian’s name.
17:14 the subscript 16 actually is the base of the number, so that is 20 in base 16 (hexadecimal)
I know someone who, when they were 12 years old, got a mouse. His dad called them to see if there was a device driver to go with it and the response was that if his 12-year-old didn't know how to write a device driver for it then he didn't deserve to have a mouse. Ah, happy times. I do miss having schematics for electronic devices though.
The control circuitry for my coffee maker failed the other day which was no big deal because I wanted to control it via networking, 12V and an inverter anyway but the company wouldn't even tell me what the wires were because "it would invalidate my [non-existent] warranty" and "for safety reasons".
That's why I tend to use very old electronics stuff. I can get schematics, and I can repair it. No amount of 'new' and piles of sophisticated features is of value if something doesn't actually work and can't be fixed.
Reminds me of a certain type of Linux head who insists you compile everything and somehow know not to accept the default compiler flags for 1 in every 12 package..!
Someone watches Louis Rossmann.
@@ImpetuouslyInsane Yes but I wouldn't touch Apple's overpriced, underspeced and locked down products with a 10' pole. No prizes for guessing my OS of choice!
Really enjoying this series. My computing history starts with the VIC-20 and Apple II+ so I have virtually no exposure to something like this. I like to be able to appreciate what the people before us had to go through to enjoy the hobby or process actual work at a company.
If you ever run out of things to fix (haha, I know) I'd be fascinated to see what you could do with late 70s early 80s arcade game PCBs. There's lots of variety there as, especially early on, the boards were basically single purpose computers made for just playing that one game. The concept of "cartridges" or something similar didn't show up until maybe Sente in the early/mid 80s as far as I know.
This is so much fun! I'm enjoying your journey with this computer. I can't wait to see it run basic!
Way back then I built a Z80 system from magazine plans. The 4K RAM card used 2102s.(1Kx1) I designed a new version using 2114 chips (1Kx4). I keep thinking about digging it out and doing an "anachronistic restoration" on it by pulling both boards and adding one of those 32Kx8 CMOS RAMS to the Eprom card.
Not only does that centralized clock save on chips, it also ensures the various clocks will be in sync between all carts, something you can't really do when every cart has its own clock.
True - and with the really moderate clock speeds of the era, you don't need to worry about adverse effects that the long connections between clock generator and clock user may cause, or even getting out of phase because the connections differ in length. With today's speeds, such an approach would be much harder to implement.
@@Colaholiker Another nice thing is, that with the 6800 bus you can easily share the bus between two masters. The CPU is only accessing when this clock is high, so the bus is free when its low.
Was for example extensively used for graphics which accessed the shared memory in between the CPU cycles.
I owned a Color Computer which was great. It had a bunch of great business software and also a cartridge called EdTasm which is a 6800 assembly language editor/assembler. This is what I learned assembly language on. In fact, a company that I was involved in used the CoCo motherboard to make engine test systems for Cummins diesel engines at the 20 acre plant near Jamestown, NY. Worked great and really reliable.
You make an obsolete computer with problems interesting. I'm impressed.
This is a pretty interesting repair. I've got a breadboard Z80 project that's similar in a lot of ways. I got a kick out of part 2 on the serial stuff bcz I knew exactly where that was headed as a oldster telecom engineer.
@ 31:31, Page 7 of the manual, it indicates which ram chip covers what region/bit of ram.
oooh! this was cool! I started using computers only in 1982 -- pretty much when the speccy came out, and it's _so_ cool to learn about computers before that!
Just remember that computers far more advanced than the ZX (or VIC) line existed before this machine was built. (The Xerox Alto of 1972 for instance, which became the inspiration for both Apple Lisa/Mac, M$ Windows and most graphical UNIX shells of the 1980s.)
If you think about it, in some ways computing has returned to this early structure with the popularity of credit card sized computers such as the Raspberry Pi and Arduino. The biggest difference is the also include a mass storage system in their tiny form factor. It requires an external terminal to access just like these old computers. They are mean to be interfaced to the real world through GPIO.
I have enjoyed seeing your process and this very old computer come back to life. I hope you can come up with a replacement for the bad chip - it would be great to see the machine maxed in memory.
Start by clicking each chip in its socket. This stuff happened back in the day too.
This video took me back to my first real job. The company had a Cromemco 8", dual floppy system that was only a bit more capable than this SWTPC. It was primitive, but at the time, it was state of the art, and I loved using it.
Just wanted to say I love your videos, you are the one who inspired me to open an old VIC-20 I had and attempt to fix it.
I'm enjoying this series so much!
I worked for Motorola Micro Systems when all the 6800 family was new as a bench technician. When we would work on memory boards. We wrote a script that would write 3's and c's to memory. Then just watch the address line cycles. Easy to figure out what was not working. I wrote a bunch of scripts for trouble shooting. I wish i still had copies. Motorola sold memory boards for $1 a byte. So a 16k memory board cost $16,000. When the 6809 came out it had better memory management, with paged memory and we came out with 32k and 64k memory boards. The 6800 memory map was flat. You can put what card at what ever address you wanted with a few exceptions. The stack was down at the bottom of memory, and the mbug.resided at the top. When 9600 baud came out we were amazed at how fast it was. We used either a Motorola terminal or a TI thermal printer. I have been looking for a Motorola Exorsiser or a SWTP computer years. There was a Basic that came.on proms. I think it was called tiny basic. I might have a set of eeproms laying around.that that i will send to you if want them. We dold a card ths5 lot of fun working on new technology. Back in the the 70. There is a trick that we would use to watch address lines. I would ground one pin and all of the address lines would start toggling. I loved those computers easy to program easy to learn to use. I think all the software that would run on an Exorciser would run on a SWTP computer.
I used to maintain a pair of Metrodata character generator that Exorcisor based. They were scrapped about two years after I left the company. Each had 6 NTSC video cards. I was told that they were given to the remaining Metrodata engineer, because the company had closed down. It also had a SMS 8" floppy disk system.for one of the computers. Dual drives and it weighed about 120 pounds. They were replaced with a bunch of Commodor 64 computers, and one 1541 drive. along with an EPG decoder/character generator to replace the local program guide. It was uplinked on a subcarrier on our WGN uplink.
The early Weather Channel interface was 6502 based. The ICs were almost a match to a VIC20.
I think that I still have a Vector Electronics protoboard for the Exorcisor bus.
Very cool Adrian...your patience and way to inspect things are admirable!! Great Job!
I love all of your videos. You are never too old to learn things.
I'm working on a heavily corroded board from a 60's camera. Heated 50% dilute Pine-Sol can do wonders. I use an ultrasonic cleaner with heater, but just hot soaking will shine up connections & boards well. It may remove weak solder mask though. But at that era, some boards don't even have it!
Good work on this one, I didn't even scream at the screen once! I did, however, pause to download those tests and take a quick look at them before you started them up.
The best memory test that I actually implemented at work was a rotating series of "100" and "011". Three doesn't divide into eight, so it really gives the memory a good shakedown. I got the idea from the old Mac Plus startup memory test where you could visibly see the pattern on the screen. It's probably the best _simple_ memory test there is. It actually caught problems in some obscure boards we got from Intel! (this was in early 2001)
I'd love to see a breakdown of what those memory test programs are actually doing. It seems amazing that so few instructions are actually testing the memory in the machine! Loving this series, as it is from the era just before I started using computers (my first was a Commodore 64), so it's fascinating to see. This particular machine seems to be remarkably elegant, although I'm not familiar enough with its contemporaries to know how special the SWTPC is.
I'd guess it's not much more than an idiot simple 'write, read, compare, print, increment' routine using FF and 00.
When I see that computer I still think of my friend Judy, who had one. Thanks for working on it.
Not as fancy as OS9, but my friend used to run FLEX this: en.wikipedia.org/wiki/FLEX_(operating_system)
Images/Docs: www.simonwynn.com/flex
Looking at the hardware on the computer, and at risk of seeming like shill, I am reminded that Evaporust really would take that rust off pretty well. I used it on a tray of assorted hardware. It may remove black oxide, but for hardware with other kinds of plating, such as zinc-chomate, it seemed to leave it intact, while doing a pretty good job. Afterwards the hardware could be sprayed with something to protect the rust--or perhaps a thin coat of lacquer would also protect it, as long as it's sprayed outside with proper breathing protection. I prefer lacquer because it dries harder and in a shorter time. I run the remainder back through a funnel and a coffee filter--before putting it back into the container. Although Evaporust is safe, like vinegar, it's PH means that it's not good to get into cuts. I think that Rustoleum also has their own chelating rust-remover too, that might have greater availability.
Also, I had an experimental idea: cleaning boards in an ultrasonic cleaner, but with a twist, of using some Kool Mist mixture to prevent corrosion whilst cleaning. It should prevent rust from forming. Kool Mist is a fairly safe chemical that can be added to distilled/dionized water that allows steel and iron to be soaked in it to prevent rusting. It's mixed about an ounce to a quart. After cleaning, the board could be blown out with either compressed air--or small handheld leaf-blower.
So nice to see you do your diagnostics. Thank you for sharing.
Several suggestions here as to better ways to approach the problem but what you did replicated the efforts of hobbyists when this computer was new using the tools they had available. There was no laptop just a dumb terminal and each test was loaded via audio cassette (a real toss of the dice each time you hit play!). This video would have represented hours of effort but that was the hobby at the time. Adrian, even your unfamiliarity with the system is reminiscent of that of the original owner!
Several hours into this series, I've come to the conclusion that this machine is a step too far for me. Good on your enthusiasm, though, and I hope you enjoy finishing it! 👍
TeraTerm allows you to directly send files (just drag&drop the whole file into the Terminal window), so you don't need to copy/paste from the file manually.
i use that myself to load .bin files via serial onto my 65C02 SBC and it works great
I am consistently amazed by Adrian’s productivity.
Love these videos! Reminds me of the good old days of using debug to run programs on cards.
Thank you Adrian! This brings back so may good memories (no pun intended). I've used the same tools many times in the past. I actually ended up modding them to prompt for start and stop addresses. The BADDR routine in the MIKBUG ROM can be used for this. Looking forward to your next SWTPC video!
@36:12 I'm sure you are aware of it, but I think it is important to state it explicitly: You can get false *positive* readings (i.e. "is OK" when the RAM still has issues), but you can *not* get false negative readings. If the memory test claims that "memory is broken", *something* in your computer, likely the memory, acutally is broken.
PC component vendors like to claim otherwise if they don't trust your memory test and try to reject returns due to the test being "incompatible" or reporting a false reading. For example, the German computer magazine c't reported about low-quality SDRAM modules around 1999 and people started testing their RAM with extensive tests. There was a notable backlash against the c't report because some vendors were unhappy with the increased amount of "your PC has bad RAM" claim. In one of the follow-up issues, they published one or two letters to the editors by upset vendors.
That mem board was hovering dangerously over that huge capacitor
Thanks for the SWTPc videos. I built one back in college which I still have. I has some spare 21L02 chips from way-back-when. Let me know if you need one to fix that board as I think that they are a little hard to find.
Thank you! I really enjoyed this. Love the troubleshooting.
It is interesting how viewers lose interest on longer videos. I've seen this with my antique refrigeration repair videos as well.
This computer is really cool... just never seen anything like it!
Effing sexy how you found that bad chip. Earned my sub brotha!
That Liberty Electronics terminal would pair nicely with this beast.
Wow! I haven't heard of SWTP in decades.
If RAM appears bad I first reseat all socketed IC's, (machined-pin sockets are the only ones I trust,) then I look for power supply voltages on a couple of chips, then I look for clocks and refresh, then I use my laser thermometer and look for hot chips. If I find nothing, only then do I bother with RAM diags. It's quicker to do the other tests first, and RAM tests back then weren't very sophisticated. If I saw a bunch of errors I'd try to identify a hung address decoder bit or I/O buffers. Socketed chips make fixing RAM boards a breeze, slow but a breeze. Fortunately, I have a pretty good stock of old LSI and VLSI support chips to swap them in and out. If the fault is intermittent then a point-source heatgun and freeze mist are in order.
What chip is used for mem on that board? I'l look to see if I have a couple I can send you. The best person to fix antique boards is an antique tech, and I'm in my 70's. :)
Another great video! Maybe consider doing an extended version (part 2) of some of your videos for Patreon Patrons for those of us who like the long-format? An Adrian "After-Party" if you will?
Very cool. CPU cache chips off an old 486/586 motherboard make excellent SRAM boards.
Very cool! I got into computing in the early 80s, and I always wondered how one interacted with machines like this.
Excellent detective work, Adrian. It's interesting seeing how this hunk works.
Great detective job Adrian, i was watching this up to 1am in bed lol. So, sleep time as tomorrow on Monday. Have a nice week.
I am ignorant of vintage computers, however I'm digging this series.
With the ZX Spectrum being 40 years old today, in celebration I powered my childhood machine up for the first time in decades and am going through similar issues. Got it booting after replacing a RAM IC whose data pin was jamming the bus but now have more intermittent issues to look at (another IC dragging down the bus). All good fun!
Pardon me for being a semantic nerd, but bootstrapping is the process of loading a small program that in turn is able to load the main system into RAM.
ROM based computers like the ZX line and most other home machines didn't have to do that, at all. They just started, instantly.
@@herrbonk3635 Very true. I (mis)used the word “boot” to indicate that the machine successfully executed ROM code to the extent that the Sinclair copyright message appears and is accepting commands that let me try load software :)
@@graemedavidson499 Or commands that builds a program. It wasn't really intended as a game computer after all (despite the fantastic teletext style colours :D) My point was that the BASIC interpreter in ROM *_is_* the (operating) system. Loading external software is another thing, and similar to computers that does indeed "boot".
Modern computers are easier when they work, but the one I just built has gremlins. Newer hardware pushes itself so hard it's always on the edge of failure at stock clocks, but because it's consumer grade, reliability isn't a concern. Nothing adequately diagnoses itself. When something fails and you don't know which part, just buy new stuff until it works. The industry likes it that way.
@Adrian's Digital Basement If you don't have memory location info on the schematics then you can use one of the faulty chips to "map" which socket is what memory range. Use a known bad chip and swap it into each other known working socket and run the test.
That was interesting. Like to see you find a replacement for the chip. I remember my uncle working on this type of computer. And it seemed so hard to me back then for me to understand. When I was very young. Now I have worked on much harder things it does not. Just very simple. Still is hard for most people though. :P
Terrific series... really enjoying it!
I have one of those Motorola development boards MEK6800D2. It's similar to a KIM, but with a second board with a LED display and hefty keypad for input.
Superb. Love your video! Thank you for your content.
Great! Thank you... the perfect 36 minutes to spend a Saturday evening with a glass of wine and some chips.
The big difference between modern computers and ones like these is the fact you can actually dive deep into repairs, I used to repair "modern" (mostly late 90s to late 2000s) comptuers as a job, and the transition from repairable at component level to the "replace the everything" that has become the norm now was a really fast process, and it's what put me off repairing computers, they just build the parts to be used and binned, rather than maintained for life like this old beast...
I think that transition happened around the time when chips stopped failing as often, and when they did, it took a hot air rework station to replace a minimum 164 pin flat pack. ;-)
It takes a pretty hard-core repair person to trek into BGA territory. “Replace the everything” is the only valid option at scale.
@@nickwallette6201 I've removed ad replaced 288 pin MPUs without a hot air station.
@@michaelterrell Great. Are you trying to say you would _want_ to replace flat packs and BGA ICs for a living, with a soldering iron?
Lots of things _can_ be done. That doesn't mean it makes economical sense.
@@nickwallette6201 We didn't use any BGA chips, but I did change or completely resolder a lot of SMD ICs from six to 288 pins at work.. I could send them to rework, and wait. And wait. And wait some more. They intentionally hid about $7,000 worth of new boards, instead of doing the rework. and I was accused f losing or stealing them. I dug through everything at the rework area, and found every one of them in front of their boss. After that, I rarely sent anything to rework.
I could do the work right then, without taking it off my bench. I had one of the later B&L StereoZoom microscopes on a cart with proper ESD protection. I had three Edsyn Loner soldering irons. Two with the smallest standard chisel tips, and a third with a 0.015" tip along with 0.015" Ersin rework solder.
I did better work than the three women in Rework, and I did it faster. I also worked with Manufacturing Engineering to update our entire reflow soldering process. It was stuck in the 1206 era, and we had just introduced 0201 components.
By doing my own rework, I was more than twice as productive when compared to anyone at the board/module level. I also built test fixtures, and updated test procedures. A lot of this was brought on by the ISO9001 certification process. Some cards had well over a dozen versions, with a six page test data sheet. The outside 'expert' saw nothing wrong with the existing procedures, but having to pint out over seven pages and marking every line on all but six as N/A wasted a lot of paper and time. I also took the average test time for that group of boards from 7.5 hours down to 17 minute average with the new fixture and test procedure. It had 16 Sallen-Key filters for easy selection of the video output bandwidths. They were identical, in two frequency ranges. The output frequency was set with two pairs of precision resistors. Slight variations in the inter element capacitance within the circuit board required some Select In Test. One of these went to the ISS as part of a kU band Data, Voice and Video uplink. I worked on about half the boards in that receiver, both digital, analog and RF.
I'm nnot a hobbyist, I'm a retired Broadcast engineer, and I did mission critical work at remote sites with zero outside support. I did Engineering Tech work at that last job. I tested one off products. I certified new suppliers and I did failure analysis.
@@michaelterrell That's impressive. Still.. I think even you would agree that's probably not a normal situation. Right?
We're really losing the thread here. There's a lot said about how today's electronics are "disposable" and "we used to be able to work on them" as if a through-hole Ryzen were a possibility.
I'm just saying ... when you can walk into a store and buy a brand new Blu-ray player for $50, trying to get a DRAM IC off the board and replaced with another is just not economical. Same goes for replacing an Ethernet controller on a $150 motherboard.
As these things get more tightly integrated, and thus more specialized, and more difficult to work on, the tools required to test and repair them get more precise, expensive, and only attainable to a more highly-trained specialized workforce with -- frankly -- better things to do with their time. So the repair industry dries up, and there's nobody left to sell schematics and test jigs to.
So you could surgically implant a Bluetooth transceiver onto a tick's butt. Great. But are you going to do that at an hourly rate that makes it preferable to bring my sub-$100 device to you, rather than ordering a new one with free 1-day delivery?
That's my point, bud. The skills exist, but within a smaller pool of people who have spent more time honing their craft, and have way cooler toys, and aren't willing to contract out for peanuts anymore. Is that not true?
Oh! Those are Patreon names scrolling up the screen... I though my new monitor had a 60hz hum bar on the left side. Good to know. Maybe a slow "bottom ticker tape roll" would work better? And no, my name isn't there yet, sadly :O\ Thank you for the video. Very COoL kit'ness. You RoCk!
6264 8k ram on chip. And used to complain about slow serial port on 8085 as it was in software!
i think the long format videos are good for things like this since it's not a device featured on the channel alot
I love older computers. I hope to see more. Right now I'm trying to get my hands on 2 or 3 special systems. compupro 8/16. And hopefully post a video. But trying to find someone that would be willing to donate one is impossible....
Excellent video and work! Waiting for the next one
really enjoying this series
Apparently the guy who founded Smoke Signal Broadcasting was a program director for CBS Radio in Hollywood. They later made 68K UNIX systems but they sold very poorly.
20:08 "Computers are simpler now...." - Well, they are when they work, but the average user has no chance if they stop. A tinkerer could figure out a hardware fault by swapping boards in a desktop pc, but if Windows decides not to play, it's a whole different ball game. Tracing bad RAM chips on a board is child's play in comparison.
I think that RAM board can be replaced with a 6264, 74HCT138 and 7805. Could provide 8K bytes of RAM of course.
Damn I like the aesthetic of the single sided pcbs on a dummy board essentially
i recently saw a double floppy disk unit of the swtpc in the exact same design and case (would guess it was 2 8 inch side by side). it was just one picture on the internet, sadly i forgot the URL. Still thought might be worth mentioning
Are you referring to the Motorola D-2 kit? With help from a engineer friend I built a 6800 computer using the D-2 Kit back in 1979.
I just remembered this little tide bit if you are programming the 6820, paralllel chip there was a bug that caused data corruption. The bug was fixed when 6821 came out. For the 6820 you had to do a reset before writing to a register.
IIRC someone (SSB maybe) offered a video card for the SWTP 6800 computer, but it wouldn't have worked with the MicBug monitor, however there were latter versions of that rom offered.
Now I wonder, while doing the troubleshooting in this way, using the tools that were available back in the day is an experience of its own, since all the chips were socketed, couldn't you just run all of them through the Retro Chip Tester?
I have some old ram testers...but not that old..unless you desolder the chips and test 1 at a time.
With the 2102 RAM chip being a 1K x 1 device, you actually have 3 banks of 1K bytes of RAM. By jockeying the bad chip around to the highest location (7C00 hex) you could have used the board as a 3K byte board.
"Smoke Signal Broadcasting" is a rather ironic name for an electronics company!
I prefer the Joe's Shoe Repair memory board.
They made their own 6800 system called the Chieftain which was fully compatible with the SWTPc 6800. And I believe it was available with a built-in Shugart SA400 floppy drive and DOS68.
Having "smoke" anywhere in the name of an electronics company is NOT a good idea 😂
Back in those days, the early home computer biz had a definite counter culture vibe to it.
Как же весело и интересно было раньше жить.
Good on you for respecting your viewer's time. My threshold is around an hour. There are live streams that I don't watch (live or after the fact) because they are way too long at two or three hours. And those are not jammed pack, as they have filler.
As much as I would enjoy a very long version of this series, you are very right as a video that long would end up in my "I want to watch this when I have time" pile. Guess what? That turns into the "I never got to it" pile.
I'm surprised you don't have any 2102s in your collection. As I recall ,those were the most common RAM chip in computers of this era, before the 41xx series DRAM chips came to dominate with their higher capacities.
Nice video, great work! BTW, I loved also longest video, no problem if one hour long :) Thanks Adrian 👍
12:51: If I understand correctly, this means it's big-endian, right? Am I wrong?
Correct. Motorola used big endian in 68xx and 68xxx series.
@@robertdixon8238 Thank you. :)
(Also, I'm facepalming a little at my own stupidity to have not caught on to the obvious M6800-M680000 connection, because I kind of knew that about the M68k.)
I saw that MAME supports the SWTPC 6800 computer and ROMs. Must try that. :)
I would have just pressed down on each chip to start with you tend to find with time they magically work there way out of there sockets. If that didn't work then I would have popped each one out and refitted. I don't think I have ever need to use dexoit. Anyway great to see an old machine coming to life.
Working with RAM chips brings back... good memories. 😃
Adrian, Love your vids. Please get a spray can lid and cover that capacitor. Every time you held a board over it with your hand under it, I was having palpitations.
I love these old machines. With all the chips on the memory board in sockets I'm surprised you didn't test them all. I don't know if it would have saved time or not.
This is badly making me want to start working on my CompuPro 8/16 S-100 system again. I think the only ROMs in my system are for floppy booting, I wonder if there are some diagnostic ROMs out there I could find?
mr adrian basement have you tried mounting your camera higher to capture more (wider) of the work bench?
I have a an TRS-80 model 1 and it has video memory issues and I was wondering if I could stack the chips to fix the video issues. I don't have the skills or knowledge that you have to figure out which chip(s) is bad. Would stacking fix it? Thanks and keep the videos rolling.