I wasn’t sitting in front of one of *These* computers, but I was sitting in front of (I think) an Imsai 8080 about then, and it had a prompt like that. I’m not sure if I was a sophomore or freshman then, but I knew some people who had a small (computer) store in Upland, CA - and if I had had money enough, I would have gotten one!
Oh yeah. Hours of work, frustration, testing, debugging, more testing and then one day, as Adrian tends to put it, "IT FREAKIN' WORKS!" This is probably what building a project car is like.
I built one of those in 1975, still have it & it still works. But now it has dual 3.5" 720k floppys on it & 64k of RAM. The thing about SWTPc computers in 1975 is they were reliable while the Altair's & IMSAI's were anything but!
I joined SWTPC in the summer of '83, and these early units were legendary. By the time I got there, the 6809-based systems were in the mainstream, with versions that ran FLEX, and others that ran the multi-user UniFlex. It was always fun to visit the 2nd floor of the production building on the days that the wave-solder unit was fired up for a run.
Computer repairs like this really help someone like me understand how the basics of computer hardware work! Thanks so much for showing us this repair! The simplicity of this machine really helps remove some of the unnecessary complexity when starting to learning about repairing hardware, and troubleshooting based on signal paths! As an audio engineer/mixer/sound designer, who also likes tinkering with old audio gear, I understand the importance of understanding a machines signal path, it’s the first thing I review when troubleshooting hardware for both fixing faults, and fixing issues when recording, especially with old mixers, preamps, patch bays, tape machines, and external gear like EQ’s and compressors! Repair of simple computers like this, really help strip away any of the confusion arising from complexity, and let’s someone like me actually start to understand the core concepts of repair! Thanks so much for these awesome repair videos!
When I started watching this, I thought "Adrians going to have problems getting the serial connections right!" because I remember that early computer designers never really decided if their serial connections were DCE or DTE, spent many a happy hour in the early 80s at Uni soldering up adapters to cross-link the data and handshake signals. I had a little box with patch-wires that constantly was being used to diagnose the wiring! It's great to see that you have at least got to the MIKBUG prompt, you now have the most important tool you need to test all those other cards. For some reason the 6800 was popular in the 70s in European electronics magazines and SWTPC advertised strongly in magazines here, so this machine is something I remember well being advertised, but I was too young at the time to be in a position to get my hands on one, by that time they had been superceded,
the power supplies alone as well. went from bulky nasty linear supplies to switching supplies. and those got miniaturized to the point where you can now get a functional supply the size of the connector (if not smaller).
@@LordOfNihil linear power supplies are very robust, and very simple. Size is their biggest downfall. Divide and rectify, filter, then regulate. In school we went over the theory behind switching power supplies, however we were told we would probably replace a bad supply and toss the old one it rather than spend the time and money to troubleshoot and repair one. If a device was rare, the supply would be sent to people who refurbished them.
@@timmooney7528 Linear regulators also tend to have poor efficiency, hence the large heat sinks relative to their power rating. e.g. for the +5V supply shown in this SWTPC giving an unregulated ~8.6V across its output cap, so 5V/8.6V =~ 58% efficiency, not even counting losses in the transformer and rectifier diodes. Overall efficiency is probably about 50%, whereas a good modern switcher with low-loss magnetics, cycling skipping & synchronous rectification can exceed 92%.
Anyone of a certain age back in the day would have seen ads for the SWTPC in Byte, Kilobaud and other magazines. I thought about going with this but ended up building the Heathkit H8 and H9 terminal (wish I'd kept it!). Good work Adrian!
Those caps seem to act almost like a UPS! You've got me interested in that funky old machine. I love how you give equal respect and attention to all these different computers, not just the usual C64, Amiga, Mac, PC. Thank you, Adrian.👍
imagine if your computer today had switches for you to get it to boot up for the first time what a pain that would be and yet at the same time how awesome it would be for you to still do it because it would be like giving birth to that beast.
I built the exact same SWTPC 6800 from a kit in 1976 when I was a student at VCU in Richmond Va. It was to interface with ADC’s to collect instrumentation data from various electro-chemistry experiments. The 6800 was an upgrade from the DEC PDP-8e mini computer the lab had been using. I built the entire machine from a big bag of parts over several weeks. It worked perfectly the day I first powered it up. At that time, the MICBUG monitor was way more advanced than the IMSAI or Altair computers that came before it. The PDP had to be booted up by manually loading a bootstrap from the front switch register. Then the rest of boot up loaded off a DECTAPE. The Chem Dept provided a Teletype ASR 33 with paper tape reader and puncher as the MMI for the 6800. Later on I got a floppy disk board and drive for it. I built an analog to digital I/O board for the 6800 and connected it to the electro-chemistry lab gear and it worked well. I also remember manually loading a chess playing program into memory via the Teletype keyboard then saving it to the floppy. The program was written in 6800 machine code! The 6800 computer was a great machine at the time and never once failed. That it replaced a DEC PDP-8e that cost 30X more than the 6800 was amazing enough.
I do embedded development which means serial ports left, right and centre. I was shouting null modem and flow control at the screen. Also when I was at Uni we used DEC mainframes with serial terminals. I learn a lot from your channel and this is the first time I did the shouty thing.
Yep, computers in general should be DTE. (modems would be DCE) For us "old-timers" who had to mess with serial, even as late as the 90s, a null modem is the first thing to think of. I still have my mess of adapters.
This is so cool! Can't wait to see this thing hopefully doing something. I love the (relative) simplicity of these old machines. Great video as always!
What a journey! It's incredible to see this big little machine come back to life and try to communicate with the outside world. I'll be waiting for the next videos in this series! And of course, thanks a lot for your efforts, Adrian!
"All the ROM + RAM in this machine is above $8000. A15 would alwould be high." 8:16 It's also possible the keyboard actuator was a little high when this statement went out.
My school bought one of these machines in the same year as I started my A-Levels, and I was given the chance to use it even though I wasn't doing the Computer Science course. I think I had more time on it than the entire rest of the official class, and on the other equipment they had over the next two years. Fabulous experience that set me up for a 40 year career in the IT industry.
Awesome to see the computer works after just cleaning bad contacts and sorting out serial port stuff! After the first video on this computer the youtube algorithm decided I needed to see all sorts of videos about SWTP and their computers. Been quite interesting to see the early Motorola stuff that preceded the 6502 compared to the Altair and 8080 S100 clones
Terra Term... That's a name I haven't heard in a long time. A long time. But seriously, I was grinning with excitement as the prompt started working! :D And I love the expansion slot pinout is right there on the motherboard on this machine!
@@eekee6034 The reference is not Obi Wan Kenobi, where he pauses just long enough for the audience to shout "how long"? That's what I was seeing. If it was something else, then you're right I do not get it.
Capacitors with no bleed resistor can hold charge for considerable time, weeks, even months. This is not unusual with good quality capacitors when you have no load and no bleed resistor. Even small caps will bite you if they have been charged to high voltage with nothing to bleed it off.
@@Breakfast_of_Champions Most likely. At least that is still good. 🙂. Obviously no bleeder across that either so it is doing what a capacitor should do 😊
I remember when I was just barely old enough to start showing interest in my father's ham radio equipment, he had a vacuum tube Heathkit transciever he'd built. He'd let me watch as he tinkered with it, but he warned me very sternly not to touch anything inside because there could still be high voltages somewhere. I was an inquisitive kid, and he was fortunately the kind of father that believed in teaching his kids why things are the way they are rather than relying on parental fiat. So he took the time to demonstrate what happens when you charge one of those big ol' electrolytics up to 300-odd volts and then short it. Huge spark and a loud enough POP that I ended up staying very far away from high voltage stuff for quite some time. And of course, he talked about how one of those could stay charged for weeks, just waiting to give a nasty jolt to anyone that happened to brush up against its terminals. Needless to say, I have a healthy respect for the absolute necessity of bleed resistors. XD
I built one of these machines from a kit back in 1978. I expanded it to a massive (at the time) 8K bytes of RAM which allowed me to run the Motorola Co-resident Editor and Assembler in RAM and assemble and test small programs. This was my first introduction to microcomputer programmer and I learnt a lot using this machine. I still have the machine but haven't tried it out for many years. Back in the day we used to pronounce the name as Sweat Pack.
I still do not understand how these old computers work with machine language, but I am so excited to see that it works! I love watching your videos even when there are things I don't fully understand.
It'd be fun to listen to the serial com with a speaker. 300baud is 300Hz so it'd be a low tone whenever it's transmitting. Thanks for another great video Adrian! So cool seeing an ancient computer brought back to life.
Great video, Adrian. One other thing to keep in mind with a device like this. Those Molex-style bus connectors undergo quite a lot of stress when inserting and removing cards. So when inspecting a device like this, you should look at the underside of the backplane and inspect the connectors for cracked solder joints. Reflow anything that doesn't look pristine (or do them all, just to be safe). After watching tons of pinball repair videos over at Joe's Classic Video Games, I've seen that most solid-state pinball machines use these kinds of connectors for the cables and harnesses that go between boards, and it is very common to find cracked solder joints on these connectors, especially at the edges, where there is the most stress when connectors are attached and detached.
WOW man that takes me back! I am reminiscent of typing in old machine language code for the Commodore out of magazines, my introduction to machine language and the rapidity of the execution compared to an interpreted language such as the old Basic.
Awesome! Thias matches my findings: the older the computer, the higher the chance that it is still working. Most of the problems started with cost reduced parts in der 80ies.
I really enjoyed your video, although the audio seemed to drop out at times during the middle of the video. I purchased a SWTCP 6800 kit in 1976 and I built it along with the SWTCP terminal and cassette tape interface. I modified an old tube TV to accept a video input and display the video. I still have the computer, along with the terminal and cassette interface units, which I also built from kits. I also built two 24K memory boards for this computer that I designed myself using 4K static RAM chips. The last time I turned the computer on was about ten years ago and it booted up and worked perfectly with no need to do any troubleshooting. I still have all the manuals and construction directions that came with the computer, terminal and cassette interfaces, along with all my construction notes. I started by programming it in machine language, then I graduated to an assembler when that became available on cassette tape. I learned a lot from building and programming that old machine. Someone commented how exciting it must have been to see that prompt for the first time, you'll never know!
I love those classic 8-bit as well as 16-bit computers despite being born in the late 80s, as they have almost mystical auras to their case designs (which apparently hung around up to the Pentium age, around '95 - '96), and they were so simple that you can literally make a full 8-bit computer on a shoestring budget today (yes, 6502 and Z80 CPUs are still made - I suspect they are going to be here to stay).
the HD64180 or Z180 would make a good Z80 compatible retro system, but slightly more complicated. Emulators are a good start point for getting into CPU tech.
Ben Eater actually goes through building a 65C02-based computer on a breadboard on his channel. I think he also sells kits so you can follow along with his videos. It's an interesting look at the fundamental principles of computing.
Adrian's reaction when stuff actually starts working might be one of the most genuinely positive things on TH-cam. 😃 Seeing as home computing went from pre-kit homebrew to Apple/CBM in about five years, I'm not surprised the SWTPC 6800 is mostly forgotten. Sure people know the Altair, known for major firsts, and War Games cements the IMSAI into our memory, but … who remembers the SWTPC today, save for the people who used them? That's why I love this channel. I get to watch history come back to life with 40% less RIFA smoke. Which reminds me… *glares at Apple IIe*
I was given a second hand SWTPC 6809 SS-50 system and home-brew terminal back in the mid 80's when I was just starting university here in Australia. I seem to recall it had 64K RAM with bank switching, and a pair of both 8" and 5.25" drives. The 8" drives almost never worked (annoying because my copy of Adventure was only on an 8" floppy) and the 5.25" drives were also a bit flaky, and would require powering on & off multiple times to get them working. I still managed to run Flex and wrote a bunch of assembly code and university assignments on it. I even modified an I/O card to drive a couple of relays to add auto-dialing and auto-answer on the very simple (Bee)modem I had. I only had basic electronics troubleshooting knowledge and tools at the time, although I had managed to heavily modify my VIC-20, and also built a couple of custom Z-80 computers. I wonder how many of the problems I had back then were poor contacts (SS50 bus connectors were awful). The floppy controllers were just very unreliable and I suspect it may have been because the crystal oscillators were not starting up reliably.
Just wanted to say that I love the breadth of your channel. I mean, it's all tech, but it's really all quite diverse in the skills demonstrated, really teaches me a lot of practical tricks along the way. Thanks for the entertainment and the education.
This was the first computer I used when I started as a programmer in 1982. This computer had 64K in it, a double floppy, and ran an operating system called Flex. We had 4 users attached to the machine through RS232 Daisy terminals, all processing their own applications. It was quite a machine. We had it's bigger brother too, it was a 68020 based machine, with 256K , twin 8" floppts and a 20Mb Hard drive. The manufacturer SWTPC, even sold a desk to install the computer and drive into. This larger machine ran UniFlex. Those were the days...
IIRC the molex pins were the weak point as these aged. We didn’t have Deoxit then…it is exciting to see you get it working. It was a magic time when many, many people’s reaction was “Why would anyone want a computer at home?”
The pins are tin coated. He sanded most of that off. I would have retinned the ICs, not sanded off the tinning on them. I use a small solder pot to clean and retin components. I use a large (Esico Triton 75T) to remove ICs and though hole parts from scrap PC boards.
Yep, sanding is the wrong thing to do. I've used a typewriter eraser on them. Incidentally, the GMX brand (of SWTPC compatible computer) used only gold molex pins.
Well, seeing you use TeraTerm made me feel somewhat at home. (Or more like at work.) I still use it there on a daily basis as the terminal of choice when interfacing the platforms I do embedded development on. While Putty may be more up to date, it seems to have some issues with VT100 control codes, which is why I can't use it for everything that I need. However, TeraTerm has a weird bug in its YMODEM implementation (yes, we still use this as an initial loading tool to get data onto hardware that hasn't support for much else yet). I would have to look up what the exact problem was (I spent a few days with a logic analyzer to find out that it basically created a mismatch between the "you can transmit" requests and the ACKs that it sent, causing things to get out of sync. It made me seriously happy seeing that you get this old machine working again, and it is fascinating that all issues so far boil down to a bad connection.
The May 1977 issue of Interface Age Magazine contained a "Floppy ROM" copy of 4K basic for the 6800 computer. You copied this from your record player to a cassette tape then loaded it onto the computer using a "Kansas City" stranded interface. I did this all from home built hardware.. It was fun in those days!
Thanks for taking us through the fault finding journey. I still consider dirty connections as a fault even if you had no faulty parts. You still used a logical approach to locating those dirty connections.
Very.... very cool. Wayyyyy back, I did so much serial interfacing between devices.... used the various little breakout boxes that were available... but I remember little of it now. Great troubleshooting... yet again!
Great to see this classic on the way to full functionality! Imagine using one of these back when it was new, because it would have likely been the first computer you had ever seen, and even the meager performance by today's standards would have seemed amazing given no experiential basis of comparison.
Ah. We are back on the "ten times + De-Oyd" Level with this old gear. Nice. I love that sort of stuff. Thankfully it seems well documented. Thanks for sharing !
SWTP made a number of kits that were featured as construction articles in Radio-Electronics magazine during the mid '70's. The CT-1024 terminal or "TV Typewriter II" was the usual terminal that would be used for this computer. I actually built that terminal from the RE construction article using wire wrap sockets on Vector board. It had add-ons like serial cards that could communicate with pre-built processor boards like the Synertek Sym 1 or the Kim 1 which ran 6502 processors.
Can't tell you how many times putty has screwed me in diagnosing serial communications. Terra Term is my go-to for anything connected to an actual serial port.
you made me travel in time ..I recall seeing that computer advertised in Popular Electronics ..Or Byte magazine ..but looks familiar to me !.well i was a kid you know .I couldn't afford any of those machines anyways..But i wanted them all .
I'm glad you were able to get this working; it reminds me of my Altair 8800. FYI: the red scope trace is difficult to see (to me, anyway) so if you can the change color (yellow or white?) that would be great. Thanks.
You'd think of an Apple IIe here. I think back in the days, the cables coming out of the computer were supposed to be long...like any other household equipment.
I saw one of these at east Texas state university in the seventies. My family owned a KIM1 and we were soldering together an 8k ram board. My brother and parents had started a company called Micro Software Specialists.
I have the Motorola M6800 single-board evaluation kit, also with the MINIBUG/MIKBUG ROM. It took me a little while to figure that it automatically adds filler-characters like spaces and some linebreaks.
More likely the power cord shown in the movies weren’t the real power cord at all but a dummy one, with the real one being hidden under a table or inside the casing. This allows for retakes on different angles for as long as you need without having to plug it back in and recharge the caps.
@@kaitlyn__L The joke here was the capacitor is so big it could be used to power evil computers. But your right about the party trick and a double chord, can't see any more ways :)
The SS50 and SS30 0.156" pitch connectors look tougher than the 80 family S100 gold fingers at the beginning and as time goes by they are notorious in terms of reliability. 68xx(x) were my favorite CPUs, unfortunately the tools for me to make a living were all 80's and later on 80xxx based. I still have a similar SS50 bus system having 6809 CPU board from early 1980's that hasn't been powered up for more than 30 years, hope some day I can boot it up again running OS9.
Its so hard to imagine a time when your options for input-output were so limited. I/O cards offered an optional 20ma current loop output for a teletype machine which were available surplus due to the amateur radio community. These gave you input, output, and mass storage but one’s significant other made you keep it in the basement due to noise and weirdness. Real terminals were commercial items and very expensive. There was no internet so you relied on magazines like Byte and 73 Microcomputing for even the most basic concepts and troubleshooting.
I had a Compupro system in the early 80s that had a similar power supply. In the SWTPC you observed that the voltage did not drop when the mains was disconnected. If my system was running and a momentary power outage occurred, you could hear the fan speed drop a bit, but the system kept on going.
I was just made aware today that deramp5113 created a complete playlist about the SWTPC 6800 computer (starting in Mar 2020) starting with it's history and showing a base configuration (CPU, RAM and IO) and continuing with using it with various peripherals and comparing it's OS with CP/M. It was fascinating to watch after following along with the detective story of getting this one working!
Amazing, grand, old computers maid to last for so long ! Life time, robust, today systems only reliable untile soon outdated more stressed out. Entousiast, understanding these systems, lovely to once more experience these, allthough actual use to be seen !
Imagine how exciting it was for someone in 1975 to see that same prompt. Great project. Fascinating stuff.
I wasn’t sitting in front of one of *These* computers, but I was sitting in front of (I think) an Imsai 8080 about then, and it had a prompt like that.
I’m not sure if I was a sophomore or freshman then, but I knew some people who had a small (computer) store in Upland, CA - and if I had had money enough, I would have gotten one!
Oh yeah. Hours of work, frustration, testing, debugging, more testing and then one day, as Adrian tends to put it, "IT FREAKIN' WORKS!" This is probably what building a project car is like.
I built one of those in 1975, still have it & it still works. But now it has dual 3.5" 720k floppys on it & 64k of RAM. The thing about SWTPc computers in 1975 is they were reliable while the Altair's & IMSAI's were anything but!
@@knghtbrdYeah. It was fun. Unlike the soulless tech we have today.
I joined SWTPC in the summer of '83, and these early units were legendary. By the time I got there, the 6809-based systems were in the mainstream, with versions that ran FLEX, and others that ran the multi-user UniFlex. It was always fun to visit the 2nd floor of the production building on the days that the wave-solder unit was fired up for a run.
Computer repairs like this really help someone like me understand how the basics of computer hardware work! Thanks so much for showing us this repair!
The simplicity of this machine really helps remove some of the unnecessary complexity when starting to learning about repairing hardware, and troubleshooting based on signal paths! As an audio engineer/mixer/sound designer, who also likes tinkering with old audio gear, I understand the importance of understanding a machines signal path, it’s the first thing I review when troubleshooting hardware for both fixing faults, and fixing issues when recording, especially with old mixers, preamps, patch bays, tape machines, and external gear like EQ’s and compressors! Repair of simple computers like this, really help strip away any of the confusion arising from complexity, and let’s someone like me actually start to understand the core concepts of repair!
Thanks so much for these awesome repair videos!
ditto! I am ok replacing a screen in a laptop and some basic stuff but this stuff makes it so much clearer if the WHY sometimes
When I started watching this, I thought "Adrians going to have problems getting the serial connections right!" because I remember that early computer designers never really decided if their serial connections were DCE or DTE, spent many a happy hour in the early 80s at Uni soldering up adapters to cross-link the data and handshake signals. I had a little box with patch-wires that constantly was being used to diagnose the wiring!
It's great to see that you have at least got to the MIKBUG prompt, you now have the most important tool you need to test all those other cards.
For some reason the 6800 was popular in the 70s in European electronics magazines and SWTPC advertised strongly in magazines here, so this machine is something I remember well being advertised, but I was too young at the time to be in a position to get my hands on one, by that time they had been superceded,
It's fascinating to see how computers have evolved since 1975. I really enjoyed the video; thanks Adrian.
@Don't read my profile photo bot
Actually, it’s still the same just scaled up.
the power supplies alone as well. went from bulky nasty linear supplies to switching supplies. and those got miniaturized to the point where you can now get a functional supply the size of the connector (if not smaller).
@@LordOfNihil linear power supplies are very robust, and very simple. Size is their biggest downfall. Divide and rectify, filter, then regulate. In school we went over the theory behind switching power supplies, however we were told we would probably replace a bad supply and toss the old one it rather than spend the time and money to troubleshoot and repair one. If a device was rare, the supply would be sent to people who refurbished them.
@@timmooney7528 Linear regulators also tend to have poor efficiency, hence the large heat sinks relative to their power rating. e.g. for the +5V supply shown in this SWTPC giving an unregulated ~8.6V across its output cap, so 5V/8.6V =~ 58% efficiency, not even counting losses in the transformer and rectifier diodes. Overall efficiency is probably about 50%, whereas a good modern switcher with low-loss magnetics, cycling skipping & synchronous rectification can exceed 92%.
Well done Adrian, fascinating video. I was shouting "Null Modem" at the screen 😁, glad you worked it out 🙂
Yes, thank you! That's the word! I was shouting "the grey cable"!!!
I was almost hoarse by the time he figured it out! 😂
Anyone of a certain age back in the day would have seen ads for the SWTPC in Byte, Kilobaud and other magazines. I thought about going with this but ended up building the Heathkit H8 and H9 terminal (wish I'd kept it!). Good work Adrian!
ISA backplane systems with a XT or AT SBC are doable for a reasonable price.
the really old ISA cards have a slight touch of their 70s heritage.
Popular Electronics had ads for these things in the mid-seventies….
Those caps seem to act almost like a UPS! You've got me interested in that funky old machine. I love how you give equal respect and attention to all these different computers, not just the usual C64, Amiga, Mac, PC. Thank you, Adrian.👍
imagine if your computer today had switches for you to get it to boot up for the first time what a pain that would be and yet at the same time how awesome it would be for you to still do it because it would be like giving birth to that beast.
I built the exact same SWTPC 6800 from a kit in 1976 when I was a student at VCU in Richmond Va. It was to interface with ADC’s to collect instrumentation data from various electro-chemistry experiments. The 6800 was an upgrade from the DEC PDP-8e mini computer the lab had been using. I built the entire machine from a big bag of parts over several weeks. It worked perfectly the day I first powered it up. At that time, the MICBUG monitor was way more advanced than the IMSAI or Altair computers that came before it. The PDP had to be booted up by manually loading a bootstrap from the front switch register. Then the rest of boot up loaded off a DECTAPE. The Chem Dept provided a Teletype ASR 33 with paper tape reader and puncher as the MMI for the 6800. Later on I got a floppy disk board and drive for it. I built an analog to digital I/O board for the 6800 and connected it to the electro-chemistry lab gear and it worked well. I also remember manually loading a chess playing program into memory via the Teletype keyboard then saving it to the floppy. The program was written in 6800 machine code! The 6800 computer was a great machine at the time and never once failed. That it replaced a DEC PDP-8e that cost 30X more than the 6800 was amazing enough.
I do embedded development which means serial ports left, right and centre. I was shouting null modem and flow control at the screen. Also when I was at Uni we used DEC mainframes with serial terminals. I learn a lot from your channel and this is the first time I did the shouty thing.
I used to work on POS equipment (in both senses of the acronym) that used serial terminals and was thinking the same thing. 😀
Yep, computers in general should be DTE. (modems would be DCE) For us "old-timers" who had to mess with serial, even as late as the 90s, a null modem is the first thing to think of. I still have my mess of adapters.
This is so cool! Can't wait to see this thing hopefully doing something. I love the (relative) simplicity of these old machines. Great video as always!
What a journey! It's incredible to see this big little machine come back to life and try to communicate with the outside world. I'll be waiting for the next videos in this series! And of course, thanks a lot for your efforts, Adrian!
bet your computer does not look that insane on the inside🤣🤣🤣
"All the ROM + RAM in this machine is above $8000. A15 would alwould be high." 8:16
It's also possible the keyboard actuator was a little high when this statement went out.
It's fun to see a computer that's simple enough that a person could understand all the parts of it.
My school bought one of these machines in the same year as I started my A-Levels, and I was given the chance to use it even though I wasn't doing the Computer Science course. I think I had more time on it than the entire rest of the official class, and on the other equipment they had over the next two years. Fabulous experience that set me up for a 40 year career in the IT industry.
Awesome to see the computer works after just cleaning bad contacts and sorting out serial port stuff! After the first video on this computer the youtube algorithm decided I needed to see all sorts of videos about SWTP and their computers. Been quite interesting to see the early Motorola stuff that preceded the 6502 compared to the Altair and 8080 S100 clones
Terra Term... That's a name I haven't heard in a long time. A long time.
But seriously, I was grinning with excitement as the prompt started working! :D
And I love the expansion slot pinout is right there on the motherboard on this machine!
*shouts* How long??!!
@@DerrickMims Since the 90s, I think, but you missed the reference. I admit it's a rather goofy reference to make in this context. ^.^'
@@eekee6034 The reference is not Obi Wan Kenobi, where he pauses just long enough for the audience to shout "how long"? That's what I was seeing. If it was something else, then you're right I do not get it.
Nice Obi-wan quote!
@@stevenfraser6180 Thanks :)
Your enthusiasm when you got it working is contagious. Keep it up, you beautiful human being!
Best way to spent a Saturday Evening: get excited about a red line popping up together with Adrian.
Capacitors with no bleed resistor can hold charge for considerable time, weeks, even months. This is not unusual with good quality capacitors when you have no load and no bleed resistor. Even small caps will bite you if they have been charged to high voltage with nothing to bleed it off.
I have a feeling it's the blue tank shell on the right that's holding all the charge😋
@@Breakfast_of_Champions Most likely. At least that is still good. 🙂. Obviously no bleeder across that either so it is doing what a capacitor should do 😊
Yes. And the Equivalent _Series_ Resistance makes almost no diffrence with the leakage either.
Yep, heard many people getting almost deadly shocks from not bleeding CRT monitors that had not been pluged into mains for weeks.
I remember when I was just barely old enough to start showing interest in my father's ham radio equipment, he had a vacuum tube Heathkit transciever he'd built. He'd let me watch as he tinkered with it, but he warned me very sternly not to touch anything inside because there could still be high voltages somewhere.
I was an inquisitive kid, and he was fortunately the kind of father that believed in teaching his kids why things are the way they are rather than relying on parental fiat. So he took the time to demonstrate what happens when you charge one of those big ol' electrolytics up to 300-odd volts and then short it. Huge spark and a loud enough POP that I ended up staying very far away from high voltage stuff for quite some time. And of course, he talked about how one of those could stay charged for weeks, just waiting to give a nasty jolt to anyone that happened to brush up against its terminals.
Needless to say, I have a healthy respect for the absolute necessity of bleed resistors. XD
I built one of these machines from a kit back in 1978. I expanded it to a massive (at the time) 8K bytes of RAM which allowed me to run the Motorola Co-resident Editor and Assembler in RAM and assemble and test small programs. This was my first introduction to microcomputer programmer and I learnt a lot using this machine.
I still have the machine but haven't tried it out for many years. Back in the day we used to pronounce the name as Sweat Pack.
I still do not understand how these old computers work with machine language, but I am so excited to see that it works! I love watching your videos even when there are things I don't fully understand.
It'd be fun to listen to the serial com with a speaker. 300baud is 300Hz so it'd be a low tone whenever it's transmitting.
Thanks for another great video Adrian! So cool seeing an ancient computer brought back to life.
I love when these old machines freakin' work! :) Your enthusiasm is fun to watch
Great video, Adrian.
One other thing to keep in mind with a device like this. Those Molex-style bus connectors undergo quite a lot of stress when inserting and removing cards. So when inspecting a device like this, you should look at the underside of the backplane and inspect the connectors for cracked solder joints. Reflow anything that doesn't look pristine (or do them all, just to be safe).
After watching tons of pinball repair videos over at Joe's Classic Video Games, I've seen that most solid-state pinball machines use these kinds of connectors for the cables and harnesses that go between boards, and it is very common to find cracked solder joints on these connectors, especially at the edges, where there is the most stress when connectors are attached and detached.
"It freakin' works!" Love hearing those words. 😉
fantastic video. Fixing these 70s micros shows real dedication to retro computing. can't wait for the minicomputer repairs :)
Your excitement is so much fun to witness Adrian!
We're so used to chip failures on ADB, no one would've even guessed the chips were fine - lol -.
Fun to see. I was an old S-100 bus guy and wish I had my old computers. Great video.
WOW man that takes me back! I am reminiscent of typing in old machine language code for the Commodore out of magazines, my introduction to machine language and the rapidity of the execution compared to an interpreted language such as the old Basic.
Awesome! Thias matches my findings: the older the computer, the higher the chance that it is still working. Most of the problems started with cost reduced parts in der 80ies.
I really enjoyed your video, although the audio seemed to drop out at times during the middle of the video. I purchased a SWTCP 6800 kit in 1976 and I built it along with the SWTCP terminal and cassette tape interface. I modified an old tube TV to accept a video input and display the video. I still have the computer, along with the terminal and cassette interface units, which I also built from kits. I also built two 24K memory boards for this computer that I designed myself using 4K static RAM chips. The last time I turned the computer on was about ten years ago and it booted up and worked perfectly with no need to do any troubleshooting. I still have all the manuals and construction directions that came with the computer, terminal and cassette interfaces, along with all my construction notes. I started by programming it in machine language, then I graduated to an assembler when that became available on cassette tape. I learned a lot from building and programming that old machine. Someone commented how exciting it must have been to see that prompt for the first time, you'll never know!
I love those classic 8-bit as well as 16-bit computers despite being born in the late 80s, as they have almost mystical auras to their case designs (which apparently hung around up to the Pentium age, around '95 - '96), and they were so simple that you can literally make a full 8-bit computer on a shoestring budget today (yes, 6502 and Z80 CPUs are still made - I suspect they are going to be here to stay).
the HD64180 or Z180 would make a good Z80 compatible retro system, but slightly more complicated.
Emulators are a good start point for getting into CPU tech.
Ben Eater actually goes through building a 65C02-based computer on a breadboard on his channel. I think he also sells kits so you can follow along with his videos. It's an interesting look at the fundamental principles of computing.
Adrian's reaction when stuff actually starts working might be one of the most genuinely positive things on TH-cam. 😃 Seeing as home computing went from pre-kit homebrew to Apple/CBM in about five years, I'm not surprised the SWTPC 6800 is mostly forgotten.
Sure people know the Altair, known for major firsts, and War Games cements the IMSAI into our memory, but … who remembers the SWTPC today, save for the people who used them?
That's why I love this channel. I get to watch history come back to life with 40% less RIFA smoke. Which reminds me… *glares at Apple IIe*
I was given a second hand SWTPC 6809 SS-50 system and home-brew terminal back in the mid 80's when I was just starting university here in Australia. I seem to recall it had 64K RAM with bank switching, and a pair of both 8" and 5.25" drives. The 8" drives almost never worked (annoying because my copy of Adventure was only on an 8" floppy) and the 5.25" drives were also a bit flaky, and would require powering on & off multiple times to get them working. I still managed to run Flex and wrote a bunch of assembly code and university assignments on it. I even modified an I/O card to drive a couple of relays to add auto-dialing and auto-answer on the very simple (Bee)modem I had. I only had basic electronics troubleshooting knowledge and tools at the time, although I had managed to heavily modify my VIC-20, and also built a couple of custom Z-80 computers. I wonder how many of the problems I had back then were poor contacts (SS50 bus connectors were awful). The floppy controllers were just very unreliable and I suspect it may have been because the crystal oscillators were not starting up reliably.
I've got red SWTPC 6800 ring binders on a shelf under my computer desk :D
Just wanted to say that I love the breadth of your channel. I mean, it's all tech, but it's really all quite diverse in the skills demonstrated, really teaches me a lot of practical tricks along the way. Thanks for the entertainment and the education.
This was the first computer I used when I started as a programmer in 1982. This computer had 64K in it, a double floppy, and ran an operating system called Flex. We had 4 users attached to the machine through RS232 Daisy terminals, all processing their own applications. It was quite a machine. We had it's bigger brother too, it was a 68020 based machine, with 256K , twin 8" floppts and a 20Mb Hard drive. The manufacturer SWTPC, even sold a desk to install the computer and drive into. This larger machine ran UniFlex.
Those were the days...
IIRC the molex pins were the weak point as these aged. We didn’t have Deoxit then…it is exciting to see you get it working. It was a magic time when many, many people’s reaction was “Why would anyone want a computer at home?”
The pins are tin coated. He sanded most of that off. I would have retinned the ICs, not sanded off the tinning on them. I use a small solder pot to clean and retin components. I use a large (Esico Triton 75T) to remove ICs and though hole parts from scrap PC boards.
Yep, sanding is the wrong thing to do. I've used a typewriter eraser on them. Incidentally, the GMX brand (of SWTPC compatible computer) used only gold molex pins.
@@wa4kdc I used Brasso or polishing compound on edge connectors but just enough to remove the oxides.
Well, seeing you use TeraTerm made me feel somewhat at home. (Or more like at work.) I still use it there on a daily basis as the terminal of choice when interfacing the platforms I do embedded development on. While Putty may be more up to date, it seems to have some issues with VT100 control codes, which is why I can't use it for everything that I need. However, TeraTerm has a weird bug in its YMODEM implementation (yes, we still use this as an initial loading tool to get data onto hardware that hasn't support for much else yet). I would have to look up what the exact problem was (I spent a few days with a logic analyzer to find out that it basically created a mismatch between the "you can transmit" requests and the ACKs that it sent, causing things to get out of sync.
It made me seriously happy seeing that you get this old machine working again, and it is fascinating that all issues so far boil down to a bad connection.
Loved your excitement when you got into the monitor for the first time. :)
Excellent work with the persistence and investigation!
the simplicity makes it absolutely fascinating !!!!! thank you for sharing !!!!! It Freaking Works !!!!!!
The May 1977 issue of Interface Age Magazine contained a "Floppy ROM" copy of 4K basic for the 6800 computer. You copied this from your record player to a cassette
tape then loaded it onto the computer using a "Kansas City" stranded interface. I did this all from home built hardware.. It was fun in those days!
This is why I like old tech, it just keeps going. :)
...umless is says MOSTEK on it.
Thanks for taking us through the fault finding journey. I still consider dirty connections as a fault even if you had no faulty parts. You still used a logical approach to locating those dirty connections.
Very.... very cool. Wayyyyy back, I did so much serial interfacing between devices.... used the various little breakout boxes that were available... but I remember little of it now. Great troubleshooting... yet again!
What a fascinating machine! Until recently, I didn't even know it existed. Looking forward to more videos about it and its different expansion cards.
Thanks for this brilliant video again Adrian! I love the way you talk us thru the problem solving, it's very informative :) Keep it up !!!
So awesome to see the SWTPC 6800 come to life!
We had one of these at work. I used to have a ton of software for it - compilers, assemblers etc. I wish I had kept it now.
Your enthusiasm is infectious! :)
Great to see this classic on the way to full functionality! Imagine using one of these back when it was new, because it would have likely been the first computer you had ever seen, and even the meager performance by today's standards would have seemed amazing given no experiential basis of comparison.
just awesome would love to see more of this machine!
Holy no smoking! Love seeing that old machine live again.
Man, seeing this thing come back to life was cool.
One of the most fantastic and exciting things I have ever seen. Brilliant.
Ah. We are back on the "ten times + De-Oyd" Level with this old gear. Nice. I love that sort of stuff. Thankfully it seems well documented. Thanks for sharing !
This is very cool -- thanks for putting in the effort to get this working again!
Very cool. Very neat to see this machine up and running!! Great work and video!!!!!!!!!!!!!!!!!!!!!!!!!
SWTP made a number of kits that were featured as construction articles in Radio-Electronics magazine during the mid '70's.
The CT-1024 terminal or "TV Typewriter II" was the usual terminal that would be used for this computer. I actually built that terminal from the RE construction article using wire wrap sockets on Vector board.
It had add-ons like serial cards that could communicate with pre-built processor boards like the Synertek Sym 1 or the Kim 1 which ran 6502 processors.
Can't tell you how many times putty has screwed me in diagnosing serial communications. Terra Term is my go-to for anything connected to an actual serial port.
Literally the coolest thing I saw today!
This will be an interesting series. This thing was out of my reach when it was new, so seeing one actually work is really kinda cool.
WOW, what a piece of history
you made me travel in time ..I recall seeing that computer advertised in Popular Electronics ..Or Byte magazine ..but looks familiar to me !.well i was a kid you know .I couldn't afford any of those machines anyways..But i wanted them all .
I'm glad you were able to get this working; it reminds me of my Altair 8800. FYI: the red scope trace is difficult to see (to me, anyway) so if you can the change color (yellow or white?) that would be great. Thanks.
Excellent! I am really looking forward to the next episode.
This is an amazing piece of computer history, great to see it's working again. Look forward to seeing future updates on this beast
I wonder if it would be worthwhile to mount a DE-9 connector directly to the chassis instead of having to mess with the existing DB-25 connector?
You'd think of an Apple IIe here. I think back in the days, the cables coming out of the computer were supposed to be long...like any other household equipment.
Serialicious stuff. Looking forwards to more on this.
Data bit 0 looks to be short circuited to Data bit 3. The half wave signal is common when feeding from two short circuited outputs
This was so exciting, I feel the joy when you are successful with the tests and repairs.
putty has options to imply
on
, and the other way around. (it defaults to ENTER =
unless told otherwise by the peer)
I'm starting to love these pre-standardized PCs from the 70s lol
I’ve also had issues with putty not sending characters properly over serial. But only with specific devices
Always nice to see exotic equipment working nice, good :)
Congrats, nice work. This encourages me to try to fix my Commodore 202.
This was so much FUN!!! Thanks!
I saw one of these at east Texas state university in the seventies. My family owned a KIM1 and we were soldering together an 8k ram board. My brother and parents had started a company called Micro Software Specialists.
I have the Motorola M6800 single-board evaluation kit, also with the MINIBUG/MIKBUG ROM. It took me a little while to figure that it automatically adds filler-characters like spaces and some linebreaks.
5:18 so thats how they made evil demon computers work in movies even when the plug is pulled out.
Just a massive capacitor
More likely the power cord shown in the movies weren’t the real power cord at all but a dummy one, with the real one being hidden under a table or inside the casing. This allows for retakes on different angles for as long as you need without having to plug it back in and recharge the caps.
@@kaitlyn__L The joke here was the capacitor is so big it could be used to power evil computers.
But your right about the party trick and a double chord, can't see any more ways :)
Kudos on your success!
The SS50 and SS30 0.156" pitch connectors look tougher than the 80 family S100 gold fingers at the beginning and as time goes by they are notorious in terms of reliability. 68xx(x) were my favorite CPUs, unfortunately the tools for me to make a living were all 80's and later on 80xxx based. I still have a similar SS50 bus system having 6809 CPU board from early 1980's that hasn't been powered up for more than 30 years, hope some day I can boot it up again running OS9.
Those molex pin connectors are notorious for having cracked solder joints on the PCB. Phase Linear preamps were full of them, too.
Its a lever action thing with the single sided no via hole.
I saw a lot of them with a burnt pin on surplus 4" NCR monitors from bank equipment. That's why they were sold for $1 each.
Looking good, probably should get my SWTPC clone out, see if it will boot it's OS.
A great video as always Adrian,
Keep up the amazing content.. many thanks
Love seeing this work!
It is pretty amazing that there were no major hardware failures, just some corrosion. I'm really curious to see what you can do with this machine!
Adrian, you need to sell T-shirts with the phrase: "IT'S WORKING!!! IT'S FREAKIN' WORKING!!!"
Its so hard to imagine a time when your options for input-output were so limited. I/O cards offered an optional 20ma current loop output for a teletype machine which were available surplus due to the amateur radio community. These gave you input, output, and mass storage but one’s significant other made you keep it in the basement due to noise and weirdness. Real terminals were commercial items and very expensive. There was no internet so you relied on magazines like Byte and 73 Microcomputing for even the most basic concepts and troubleshooting.
Very enjoyable troubleshooting :)
I had a Compupro system in the early 80s that had a similar power supply. In the SWTPC you observed that the voltage did not drop when the mains was disconnected. If my system was running and a momentary power outage occurred, you could hear the fan speed drop a bit, but the system kept on going.
I was just made aware today that deramp5113 created a complete playlist about the SWTPC 6800 computer (starting in Mar 2020) starting with it's history and showing a base configuration (CPU, RAM and IO) and continuing with using it with various peripherals and comparing it's OS with CP/M. It was fascinating to watch after following along with the detective story of getting this one working!
Awesome work.
Thanks so much for sharing. 😉👌🏻
Deoxit that socket baby! I'm assuming it'll be able to run BASIC once it's whole again?
Amazing, grand, old computers maid to last for so long ! Life time, robust, today systems only reliable untile soon outdated more stressed out. Entousiast, understanding these systems, lovely to once more experience these, allthough actual use to be seen !
I noticed that at 25:42 it printed "A00 89", not "A000 89".
Wow, incredible 😀😀😀👍👍👍