This TRS-80 Color Computer is dead, so let's fix it
ฝัง
- เผยแพร่เมื่อ 30 ก.ย. 2024
- #trs-80 #repair #coco
On today's video, we have a repair of a TRS-80 Color Computer 1 -- something never featured before on the basement. The computer has a checkerboard pattern, so let's figure out why!
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SMMC 0035 where I unbox and do initial testing of this Coco 1:
• 0035 We have a broken ...
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Really appreciate the variety on this channel. Seems like some retro channels are Commodore-centric, nothing against that line of computers, but I like hearing about Atari, TRS-80, Apple II, and early hobbyist computers as well. Thank you Adrian.
I totally agree. It’s the variety that really makes this channel one of the best (as well as the presentation of course).
It’s not surprising. Commodore and apple was more prevalent. Don’t know about my homeland Australia but I was PC and Amiga
@@XolaresTiberius c64s are pretty unreliable compared to say Apple or Atari which helps when you do repair videos too :-)
@@Doug_in_NC the presentation is second to none. The enthusiasm alone is worth the watch!
Agreed
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It's well worth setting up to run autonomously on your videos every few hours for the first few days after a video goes live
There's a technique to more safely pull vintage flatflex cables out of their connectors, like on the keyboard you had here. Often, due to age, the spring contacts stick to the fingers on the flatflex, and it can tear off the metal. What you do is get a bit of thin stiff plastic, like the clear stuff from a blister pack product packaging, and cut it to the width of the connector. Then, on the contact finger side, you carefully slide it into the connector, maybe using a bit of deoxit as lube. This separates the spring contacts from the fingers on the flatflex, and you pull the flatflex out along with the plastic shim. No friction on the fingers means lower chance of damage.
Very useful tip, if I ever have to deal with that situation again. Thank you!
That's some cool advice, I hae a few vintage machines to work on and this will surely come handy :).
Recently been working with something that's not quite vintage but old enough to worry about, and it has a very stiff ribbon connector that has to be removed every time I want to disassemble the device. I'll be sure to do this next time.
@@kasamialt if you take it apart frequently, it shouldn't be a big deal, this mostly applies to the case where oxidization causes the socket contacts to stick to the flex pins, increasing the probability of tearing the flex cable and/or ripping off the pins.
@@TuxraGamer The socket is very tight in this case, maybe due to cheap parts or whatever, so I still worry about damaging the contacts on the cable or even tearing it from the force required. It's a fairly standard type so I could replace it if necessary but it's soldered down at the other end so would be a pain.
A bit of CoCo trivia: the CoCo is based on the Tandy AgTerminal. A competition was held in the late 1970's amongst colleges to design a computer terminal for US farmers in the Midwest. It was supposed to dial into a central computer and supply the farmers with commodity prices, futures market information, weather forecasts and a mail system. An ultra rare Tandy AgTerminal looks just like a CoCo, with different ports (like no cartridge port), and an internal modem. Tandy won the bid to produce the competition winner (which was heavily based on Motorola 8 bit parts).
Interesting tidbit of info, thanks.
My dad (a farmer) had one of those tandy terminals. My brother and I hoped to be able to use it as a computer, but were never able to make it do anything other than what it was designed for.
I remember that, Thanks for telling the viewership that sweet little tidbit about the beloved CoCo!!!
@@mickster150arcade It would have taken quite a bit of expansion, and a different ROM. For programming the different ROM, you'd have wanted another working computer.
I always wondered why Tandy didn't pick the Z80 to build the CoCo. Maybe the AgTerminal is an explanation. It would've been cheaper for Tandy, striving to lower costs, to use the cheaper Z80 already used in its Model 1/3/4 series than the 6809. Don't get me wrong, the 6809 is a great cpu, easy to program. The CoCo was in competition with other popular low cost 8-bit computers. Using the same BASIC and some softwares from Model 1/3/4 would have saved even more money.
I never realized how much of a tech nerd I was until I started seeing these videos and knowing what you were talking about and understanding the repairs/problems, reminds me of repairing my pre-historic IBM 386 at 9 years old with an instruction manual in German.
As I recall it was pretty common on all these (1,2 and 3) for the CPU to fail if you pulled out a cart while the unit was on because the CPU pins to the cart connector are not buffered. I've fixed at least 4 units with dead CPUs like this.
The CPU and the LS783 chip could go bad doing that. Learned from experience.
as James Bond would say "Positively Shocking". but seriously as a kid I would have pulled the cartridge at some point no matter how careful I would want to be.
Crazy that the engineers didn't account for people having a brain fart or kids that didn't know better.
On the Dragon the 6809 is right up against the cartridge slot.
Thanks you very much Adrian. Always a great relaxing pleasure to watch your trouble-shooting videos. That Radio-Shack one is reminding me about my first computer shared with a good kid friend, a TRS-80 that was baught used in the south of France. We were programming it in Basic, then quickly in Z80 using the supplied editor-assembler. That was fantastic ! We had to learn English on to of Basic and Z80 programming. Then i went color with a VIC20, the Atari 800 was so great a dream, but over budget, and the 400 too bad with its film keyboard aka a ZX81. Realy pushed the VIC to its limits with the Floppy drive and some multi-cartridges extensions allowing for dumping those onto the extended RAM. I was programming in in 6502 directly in Hexacodes from a notebook to calculate the jumps, also exchanging programs on tapes via post all over Europe including behind the curtain (Poland). Then went the Amstrads CPC464 and 664 and later jumped to my first PCs build using a super powerfull 386SX16 .... Thanks again for yor chanel , i am sure that many kids of the time are watching every of your videos ;-)
That was wonderful you had to learn English to understand the manuals ! When we bought The Hobbit game for the Sinclair ZX Spectrum we had to read The Hobbit novel that was supplied to figure out how to get through parts of the game ! I hope like me, you turned a passion into a career ?!
On some early CPUs it’s not good to leave them powered without a clock when not halted. Some early 6502s were like that. So may be the SAM failed which left the 6809 locked up and it failed because of the clock issues.
Great basic diagnostic info! As for the keyboards, even if that melted keyboard isn't ideal, anything is better than the chiclet keyboard the original model has. Those things were stiff and awful to use, and made me strongly dislike the Coco when it was new.
A note about the availability of the service documentation: In most cases they were available at the stores that had the repair centers sometimes for purchase, however if not, they could be obtained by what was called "RSU" (Radio Shack Unlimited) order, which was shipped from a warehouse , or via "Fax back". Fax back was a bit more limited, and was available later on... and was only for certain sections of the manuals if I recall properly.
I can attest to how durable the Color Computer 2's and 3's are. I was a Repair Technician for a regional Radio Shack repair center from 88-89, and CoCo repairs (except for 3's needing the ASIC socket cleaned) were pretty uncommon. I could also confirm that the documentation was readily available at that time via the Service Manuals that could be ordered at the retail store.
It's pretty clear that the mod to the cartridge port was what damaged the CPU and the SAM. While hot-plugging wasn't good for a CoCo, it was tough to kill them that way.
I'm looking forward to your Dragon64 repair video, as I am building one out from a bare PCB (yes, I have 4 "spares" if anyone is interested). It's a step in my project to clone a CoCo2 board. Eventually I'd like to see if I can add the bank switching and additional RAM that the CoCo3 does via a 6829MMU (the CoCo does that all in one custom chip). I'm capturing this via a personal website, which I won't post unless Adrian agrees.
Thanks, this video was a walk down memory lane.
Dad bought the Coco 1 (16k version/chiclet keyboard) as our first computer, back when it was pretty much brand new. Until you brought it up, I didn't remember Downland, but I recognized it when I saw it. I suspect that's because Dungeons of Daggorath and Quasar Commander occupied so much more of my time.
Dad eventually did do the upgrade our to 64k (quite successfully), but never upgraded the keyboard. He was a hunt and peck typist and couldn't see what was wrong with it.
A common warning with using the CoCo was to turn it off before inserting or removing a cartridge, because there's a high risk of frying the CPU. It looks like that that's what happened.
Nice investigation. I coded in Z-80 and 8080 Assembly back in the day, and as robust an instruction set as the Z-80 had, I was still envious of the 6809 16-bit multiply in hardware. Well done! Glad you're feeling better.
This was fun! The vanilla TRS-80 was my first machine on age of 12. Get well soon! 🙂
I got the Coco2 when I was a kid with the Chiclet keyboard, and imMEEDiately wanted to replace it. Kept an eye on the Coco press (Hot Coco & Rainbow magazines) and sure enough, the melted keyboard became a Radio Shack part number that could be ordered. I remember installing it myself, with no chip swap or bodges required. And yes, it was vastly better than the original for touch typing.
Incidentally, the wear pattern suggests to me a two-finger-hunt-and-peck typist, resting their hands out of the way so they can find which key to strike.
I was thinking the wear pattern might be indicative of someone resting their hands where the arrow keys could be accessed easily (far left and far right of the keyboard).
@@Markus0021 I saw a comment to that effect below. Not much of a gamer here, but that might be the better answer.
Downland has a very fun-to-exploit bug. Some levels had jagged side walls, and it was possible to jump outside of the level through the jagged wall and progressively jump higher and higher until our hero is standing on top of the level. Jumping above the top of the screen sometimes caused our hero to become a "maker", where he left various random bits of reality behind him everywhere he went, even creating his own ropes to climb around on.
Sounds like Tron making an illegal exit from the game grid!!!
It's always satisfying to see these old computers come back to life.
In technical terms they are prehistoric. In personal terms I have a lot of skills associated with these machines. Simply firing up XRoar Dragin 32 I can immediately do things I struggle with on my Linux Mint PC. I've got a physical Dragon 32 (based on the same Motorola design) ready to run once I have a PSU. It will restore some of my computer skills once this runs.
My dad bought us a CoCo2 back in 1983 or 1984 (I don't remember exactly when) which had the melted keyboard. The first computer my dad bought for us kids was a VIC-20 which I loved to bits, but my dad didn't like it because the game cartridges were very expensive and the memory capacity was too low, so he sold the VIC-20 and bought us a CoCo2 with 64K memory from the local Radio Shack in Douglas AZ. At that time we were living in Agua Prieta, Mexico, which is a city just south of the border from Douglas AZ - I now live in Houston TX, so Howdy! I remember that the SAM (Synchronous Address Multiplexer) which coordinated so many things in the computer (DRAM refresh, video, etc.) got REALLY hot very fast and was a source of frustration for many CoCo owners because the SAM had the propensity of going bad. I am not sure because we're talking about 30 years now, but I believe some owners placed a heat sink (or two or three in a row) on top of the SAM to keep it reasonably cool.
In college I had an original silver CoCo with the chiclet keys. It had the metal joysticks that tingled when touched! I replaced it with a CoCo 2 and did some assembly programming on it, wrote some utilities like a BASIC extension to display real lowercase, etc. It was a fun machine to learn on. I was a 6809 snob because it had more/better addressing modes than the 6502 and even the PDP-11 we were learning in class (though what did it really matter when all you had was 64K!)
The two people that got me into electronics and computing were the one's that designed and made that keyboard upgrade kit for the COCO I. They gave me their old stuff once they moved on so I had tons to play with.
That 6809 was probably the most powerful 8 bit processor around, being 16 bits for a lot of the internals, but the 8086 came out about the same time which was a real 16 bit. All of the instruction set features, especially the 5 (?) addressing modes went directly into the 68000 line.
I also got an operating system called OS9 that was virtually a clone of UNIX. I later did some programming on a real mainframe UNIX system and really couldn't find a difference. It was a Multiuser/multitasking system. I once used a PC as a terminal operating a 80 char wide word processor at the same time I used a 64 char wide setting of the same program at the same time on the COCO II. The operating system actually used a single copy of the program in memory with the users totally isolated.
Because of UNIX's ability to load drivers (windows stole the idea) I was able to hook up a SCSI hard drive.
I loved my COCO.
I like watching this and want you to fix the rest of the things you had for it. I will pray you only have a cold. Everyone around me is getting Covid. They are not ending up in hospital. And get over it and then get it again later. It is going to be normal like the flu now I think. I got both shots and both boosters. And I have not got it yet. I have asthma. So I am worried about getting it if it affects my lungs.
Had it recently was fever, fatigue and only a mild cough. Lasted about a week.
@@marka1986 one of my times lasted just over a week, but another time was just over three weeks 😱
Our first computer was a CoCo 2, my dad bought it on sale. I think the 3's were coming out and he got the 2 for a good price. Thanks for bringing back memories for Father's Day weekend.
Thank you for drawing attention to the scammers.
The wear pattern on the case would suggest the previous user placed their hands to reach the cursor keys, probably a gamer.
I mentioned this on the second channel video, too. We also see clear evidence at 47:11 on this one :-)
I noticed the blue bean behind the cassette socket. It’s the cassette relay and this one is a reed type which was notorious for welding closed. Some replaced it with a regular relay. My sister and her boyfriend managed to kill my CPU, SAM and the 7404 in the disk controller by hot loading the disk controller. It can happen alright. The 6 bit DAC can generate 4 voices but no so much during gameplay as it took a lot of CPU work due to no hardware to assist it.
Great video! I hope to see more CoCo content sometime soon! I have a CoCo 2 and would like to put it to use :)
Adrian I'm not one to try to advertise for other youtubers but if you are having issues with spam, ThioJoe created a free app for content creators that allows them to mass delete spam from all of their videos comment sections at once. I would at least check out his video where he details it a little better, it was actually featured by Linus as well. I think it might help quite a bit.
I had one of these as a teenager and it is not an easy system to navigate at all, the programming was long and had to save it onto a cassette tape, that was connected to trs80, as far as it's gaming capabilities the joysticks that were designed for it were fairly decent especially for the era
Working at Tandy Computer Repair center in the 1980s i think the Tech Ref was available for current models (models currently on the sales floor) in a softcover version (available in Tandy Computer Centers not regular Radio Shack Stores)..if my memory serves me they were very expensive around $30 ($80 2021 dollars) ..In my shop we had a 8 foot long shelf over the workbench with the Service Manuals (which would be different than a Tech Ref manual) 3 ring binders for every model..the unique thing about these manuals was on the schematics for every test point there was an image of what the o-scope signal looks like for that point..The manual also contained Tandy part numbers for every single part including screws etc..These were marked CONFIDENTIAL on each page so these would not have been available to the public..
A common user mod done on CoCo 1 in the 1980's was to remove the RAM badge on the case..under it there is a hole that perfectly fits a LED to work as a power indicator..
47:15 Besides the Tandy CoCo and Dragon 32, the Acorn Atom and Vtech Laser 200 also have the same garish colours in graphics, as those computers have the Motorola MC6847 VDC chip.
Thinking back my sisters boyfriend took out my 6809E and SAM (6883) by plugging in the disk controller with power on. She wouldn’t accept liability but said exactly what they did. I got the chips replaced but the disk controller wouldn’t boot. Yup, the 7404 used as an address decoder was dead. Never hotload a cartridge or anything else.
You know you've hit the big time when scammers are impersonating you.
Downland colors toggled between blue and red (over RF, anyway), blue seems to be the desired color as things looked wrong in red. I hope you give it a shot with the Tandy deluxe joystick, it's definitely one of the better CoCo games!
Another excellent video. Thanks.
Yep, the CoCo 1 and Dragon are very similar machines indeed - both being based almost entirely off Motorola's reference design and both using the same M$ Basic - although why M$ supplied the exact same Basic to both companies but used different addressing is beyond me!
Tips:
1) Most people would say the Dragon is a better made made machine, certainly a nicer keyboard. The Dragon 32 can be upgraded / modded to a 64.
2) The only practicable difference between the machines is the addressing of the M$ basic (why M$???) and the keyboard mapping. (Ok, I/O too)
3) While a lot of software and hardware will run with either machine it's a fairly straightforward job to mod either to be 100% compatible with both:
a) Replace the ROM with a larger one containing both versions of Basic.
b) A bit of wiring to allow the keyboard to behave like both machines.
c) A switch to, um, switch between modes.
So...
Got a Dragon 32/64? Mod it to be CoCo 1 compatible - the CoCo does have a larger software library.
Got a CoCo 1? Possibly modding one for D32/64 compatibility is less compelling, but I'd say fun anyway.
Rumour is that Dragon Data made things like the keyboard mapping, BASIC tokenisation and addresses of various ROM routines different to avoid the lawyers.
The Dragon 32 has a parallel printer port. Additionally, the Dragon 64 has a serial port. Allegedly some of the last Dragon 32s to be produced are the 64 in a 32 case. Possibly with the serial port unpopulated and/or the memory jumpered to 32k. (There are similar rumours that some ZX Spectrums shipped with fully working 4164 DRAMS.)
There is a US version of the Dragon 64 called the "Tano Dragon".
I think jostling whatever is plugged into the cartridge port while the machine is turned can cause this problem. Perhaps someone bumped the multipak while using the computer.
That cartridge port mod i'd suspect caused both chips to die maybe a short to Q killed both chips especially if one of the cut wires was connected to 12V
Hopefully, you're not sick for very long. There's nothing worse than a summer cold. Get well soon.
Are you still dealing with the shoulder problem?
The documentation for the Radio Shack computer where easily obtained from any Radio Shack for very reasonable price. I paid $19.95 for the model 1000 manual which was over a inch think and contained full schematics and theory of operation. A regular Radio Shack might have to special order it but the Computer Center stores typically had the manuals in stock. Radio Shack also carried data books for the TTL / CMOS logic chips. Back in the day Radio Shack was a great resource, that changed over the years as it slowly faded into obscurity.
This is just amazing. What an amazing company! I loved my local radio shack but I never even looked at the computers they had on offer.
@@adriansdigitalbasement I never could afford to buy a computer in those days but I certainly wanted to learn everything I could about them. I ended acquiring a TRS-80 Model I & III years after they were outdated but I spent a lot of time building hardware to extend their capabilities. Watching your videos takes be back to my teens when computers where so simple and you could actually change things with moderately priced tools.
So this is quite a heavily modified CoCo. It's actually pretty cool, I'd like to see the mods retained rather than returned to standard.
The green @ symbol is ASCII 0, and the orange block is ASCII 255.
The games looked better than I expected. The cave game "Download" looked pretty good. Will be interesting to see the Dragon. In the UK I knew a couple of people who had a Dragon back in the mid 80's (one being a school teacher). I think the graphics chip in the coco and the dragon are the same as in the Acorn Atom computer.
I love your SepTandy. Please keep it up. I worked for Radio shack back in the 80's. My first computer was the TRS-80 Model 1. I still have it. I also have an original Coco, a Model 4P, various pocket computers, etc. Love your channel.
I love this channel! I learn so many things I didn't know about these old computers. I feel so much smarter and if I ever get any of these computers again, I may just be able to fix them thanks to your channel. Hope to see the 4 cartridge selector up and running too. Thank you for your vids!
Grandma was using her TRS-80 to make '80s Rock Videos!!!
Wow, never expected those two chips to fail. AFAIK, they have a history of being long lived. So, "live" and learn. Great diag session. Loved it!
I wonder if that cartridge expander could have killed those chips.
This was my first computer. I had the 4k version with the chiclet keyboard! I had it upgraded to 32k, but unfortunately there was no option at the time to switch out that horrible keyboard! I so loved that computer, and it led me to become a PC tech later in life. I did a lot of Basic programming on it as well as some really decent games! Dungeons of Daggorath was my favorite game on this system, and it was the precursor to 3D games we see now. This system led me to getting an Atari 800XL, then later the Atari 520ST. From there I went to the PC, building it myself, and was rocking a 286/12 with a VGA graphics card! Wooohoo!
Great vid as usual.. The Coco sure had ugly boot colors, I remember it bothered me back in 82.
This was a good video and I really do enjoy learning about these computers while you are fixing them. Thank you.
the red/blue color inconsistency is related to how the sync happens, sometimes it locks to the rising ramp, sometimes the falling ramp. This was (finally) address in the CoCo 3, it always boots one way, and if you hold (F1) I believe, it boots the other. The color oddity there may have something to do with that composite mod.
Adrian, a fabulous walk down memory lane. I had a UK PAL CoCo 1 in my teens - my first computer. Using the EDTASM+ cartridge and a 6809 book, and the excellent Tandy technical documentation, I taught myself 6809 Assembler. I used to poke a RAM location that switched the video page to &H0000 so I could watch what the machine was doing 'visually' on the screen in running the computer. I started writing 6809 code to produce a 7x5 pixel character set on the 256x192 resolution mode. I also wrote a 6809 program that listened to the tape port and basically listed on the screen what it found in each sound block from a CSAVE. I also (failed) to try and build a 8k RAM expansion for the cartridge port as the R/W line extends to the cartridge port - Tandy sold blank cartridge PCBs that you could mount your own chips on. I still have some Tandy reference material here somewhere. I recall a yellow manual called The Engineer's Handbook or similar that taught me so many of the TTL era digital electronic basics. Thanks so much. Really enjoyed this one.
You’ve just reminded me about creating my own character set ! It was for a Southwest technical products Corporation (SWTP) computer we had at work. I did not have the knowledge for machine code and wrote in basic various line drawing commands to create the characters.. it had the added effect of looking like a terminal running at around 300 baud. Ah, the miracle of youth!
This is like operating on a living being, very interesting work you do Sir.
Another excellent video Adrian, thank you!
This looks exactly like the TRS-80 we had when I was a kid. My dad installed the new keyboard, which made all the difference in the world compared to the horrible Chiclet keyboard. We also had an external floppy drive and a tape recorder. Great machine - we kept using it up to the late 80's.
Great video! Interesting brain connection between Sam & Max ;-)
that's it, I'll be calling the MPU "Max" now :-D
And Paula, Denise and Agnus. Can be confusing at times. 🙂
Radio Shack also had great documentation and schematics for pretty much all of the things they sold.
i have a friend who's dad used to own a TRS-80 , gave that to my friend when he moved to the Commodore 64, and then gave my friend the commodore 64 when he moved to Atari St .. that kept the machines in the family for many many years, my friend became an Amiga Fan while i became an Atari St fan 🙂
So what did I win?
He asked knowingly…
Hope you feel better soon. I caught the human malware a few weeks ago, it was a relatively mild case but it still wasn't fun. So I'm glad it's not that.
Yeah, I definitely think whatever mods those wires were related to was what killed the machine originally. Hopefully you can pick up a spare SAM chip. Or perhaps there might have been one in your many chip donations? Although knowing your luck, you'll probably just have to wait a few weeks and someone will send one in as a mail call donation!
That component on the square heat sink with the Motorola logo is a transistor (specifically a ‘series pass transistor’ in a linear regulator circuit). That could well be the 5 volt supply circuit.
That was a very satisfying repair.
Thanks!
I had a c64, it was modded with a piggy back sid chip for 6 channels, and also I did a popular conversion of a VICModem to an RS232 adapter that allowed me to connect to a 2400/9600/14.4k modem. If you ever come across those I'd love to see :) (subscribed!)
NTSC = Never Twice Same Color! Good job on getting this old girl running. Hope you can find some more SAMs and CPUs.
Very fun video, ty so much!
About the 68B09E chips, I'm in Korea and you can buy them in little bags for a couple dollars each.
Adrian, I have a special request. One of the CoCos, I believe III, had a Poke register for double-timing the CPU, which increased data processing but made the graphical output go haywire-- but haywire in a very trippy and interesting way. As a teen, I would stare at that for several minutes as a time.
Do you know this effect, and if possible could you take a video of it and put it up on TH-cam? That would be the ultimate trip down memory lane for me!
grest video! Simple fault but very interesting!
Although it wasn't really touted as a "feature", in NTSC the Atari 8-bit has artifact colour (blue and orange) in high res mode (used in a few games like Ultima III), but on PAL machines it's an unstable and unpredictable purple and green, so it looks like this machine is some sort of weird hybrid of the two. :P
Don't go for a SAM chip on Ali. They 99.9% chance say they have it, but expect to get a piece of plastic with feet only.
How were people supposed to use this computer. Seriously, 32x20 characters? OMG!
25:50 "It seems like the computer is not actually doing anything, like the CPU is not running any code. -- alright, that one is just high, ... same thing, same thing. So again, they're all just high, which just sort of reeks..."
When "just high" is everywhere, you know nothing is being done...
18:40 - I bought this exact manual right off the rack at my local Radio Shack. The more in depth service/repair manuals were a little harder to acquire, IIRC.
That is so cool. That is a perfect of example of right to repair done right. Companies like Apple should be ashamed of themselves, even if the contemporary Apple back in the 80s.
Hey Adrian, since the bad signal on that SAM chip is just a clock signal phase delayed by a fixed amount from a valid clock signal you have, you could actually bodge a fix and save the chip by tapping off the good clock you have (assuming nothing else is bad in the chip).
There are a couple of approaches I’d consider, after reading the data sheet to see how much delay you need between the two clocks:
1. Maybe a single buffer stage will just work as there is some delay through the buffer.
2. Use a chip with multiple buffer channels and string the signal through them, getting a few delay steps.
3. Use an RC time constant to delay the rise time on your tapped off signal. With a potentiometer, you’d even have a variable delay.
To prototype, you might even be able to use your virtual bench, having the scope trigger the function generator.
Might be a good video in and of itself!
Not a bad idea. I do think it’s little the chip is damaged internally though because that clock is likely used internally in the SAM as well. Still worth a try though!
In addition to that, the fact that the chip was getting REALLY hot is a bad sign.
Something is shorted in there and that something could effect and upset a bunch of other stuff.
Most concerning is the fact both SAM and MPU were dead - it's unlikely but not impossible that one killed the other, possibly in a roundabout way...
A number of your tools links are not working. for a start "DSLogic Basic Logic Analyzer:" "Universal ZIP sockets" "Plato (Clone) Side Cutters"...
This video was really useful! I have a CoCo2 with same symptoms and I had a bad CPU too. It’s still not working perfectly and I suspect the ROM being corrupted, but changing the CPU helped with the jailbar screen.
The jail bar screen is the same as black screen on the C64. There are a ton of potential problems that could cause it. I suppose the one thing is the Coco is less complex than the C64, so you have less potential issues. :-)
Try to re-seat all the chips and check the RAM, clocks and buffers first.
Bad ROM is far from impossible, but even if it seems the data is read incorrectly, it may not be it's own fault.
@47:29 This sounds an awful lot like the PDP-1. Search PDP-1 Christmas Carols for you to find out yourself. And by the way: you were actually listening to not one, not two, but _three_ simultaneous channels...! Awesome stuff!
My first home computer that I paid for myself was a Tandy CoCo 2, so the CoCo line holds a special place in my heart. Glad to see this one saved. I had two of these grey case ones back in the day, and they were in a box of computer stuff which went missing during a move.
Spectral Associates was the same company that published Commander magazine out of Tacoma, WA. (Commander was a magazine for Commodore computers)
I want to see if the Multipak Interface works... The coco1 has 12v on the cartridge, later coco2's did not, so some disk controllers that work with the coco1 do not work with the coco2. Using a Multipak not only allowed multiple cartridges, it allowed use of the older disk controllers that need 12v to work on the coco2 that has no 12v line. There was also a mod for the coco2 to output 12v on the cartridge port. It requires another 12v supply to be connected to the appropriate pin on the cartridge port,
There was a board that is rare that allowed coco3's to piggyback a 68000 )not 6800) series processor on the coco3. You removed the memory and it plugged into the memory expansion for the 512k upgrade and the MPU allowing a 68000 16 bit processor and 6809 to co-reside on the coco3. I think the exact MPU use was a 68070, but I am not sure... it was however a 68000 series MPU.
The switch on the Multipak is only used on power up.. It internally controls three lines, CTS, SCS, and CART. Inside the Multipak, each cartridge slot get it's own CTS, SCS and CART connection. On startup if the Cart line is pulled low by the cartridge, the MPU reads the cartridge ROM, and ignores the BASIC ROM chips. This is NOT used to the disk cartridge as the BASIC ROMs automatically look for the Disk ROM and integrate it into BASIC changing it from Extended Color BASIC into DISK Extended Color BASIC. CART is used only for Cartridges that auto-start, some people clipped the CART line on their cartridges so they could copy them to DISK using the Multipak.
The CTS line selects what ROM is read, the switch as I said controls CART, SCS and CTS... So if the switch is on "1", The CART, SCS and CTS from the first cartridge is used,. 2 for the second cartridge and so on. So when turned on if the Disk Controller is in slot 1, and the switch is on slot 1, you start with DISK BASIC, however some cartridges do not use all of the the SCS, CTS, or CART signals, one such cartridge is the RS-232 serial cartridge... This cartridge does not usually have a ROM chip, and is purely hardware. So SCS, so it has no connection to CART or CTS. So if CTS is sent to the RS-232, it too ignore CTS just as the DISK Controller does. Therefore both can be used at the same time.
If you have a second DISK Controller, it is possible to use both. SCS controls which hardware is used. Writing to address &HFF7F switches ports. Once that address is writtin to the switch on the Multipak is ignored. writing &H00 selects slot 1, &H11 selects slot 2, &H22 selects slot 3, &H33 selects slot 4. Using &H03 selects two different slots, Slot 1 for CTS and CART to control the ROM used, and slot 4 control SCS for hardware selected. NOTE some hardware ignores one or more of the CTS, and SCS, or does not return a CART signal. Hardware not using SCS can interfere with other hardware using the same memory address, however I have never found any hardware that conflicts with other hardware, unless corrosion has caused these lines not to connect.
I relabeled slots 1-4 as 0-3 with a sharpie so I can remember the hexadecimal number used. Oddly enough you could use 0-3, 4-7, 8-B, or C-F to control slots 1-4. Also people have build their own 2, 4, 5 or 8 slot multipak interfaces. On the 5 slot multipaks, the 5th slot does not have CTS, SCS, or CART connections, and only hardware that does not need these signals can use the 5th slot. Since the MSB and LSB of address &HFF7F are 4 bit, it would not be difficult to make a 16 port Multipak. Both MSB and LSB can have 0-F or 16 different values.
Back in the early 70’s I helped my dad build SWTP computer, from there we did mods on the COCOs. Eventually he built his own machines based on the 6800/68000 called ACORN. Let me know it you have run across one. I might be able to share on. I have the ML AC, logic, board designs and schematics!
it'd be nice if there was an easy way to convert the CoCo2 to composite. I still have mine from when I was a kid, but I don't have any TVs to use it with! This was a great video, Adrian - Thanks!
If I remember correctly, it's a very easy mod, just 2 transistors and a capacitor (or was that for CoCo1?)
Anyway there is a lot of info on this, some ready-made, some DIY - just google.
Buy a used TV with a analog tuner.
Quick Tip, Adrian - use white spirit to lift the adhesive without attacking the paint. IPA attacks silver-painted plastic - I only made that mistake once! I think you call white spirit 'mineral spirit' in the US? I've been refurbing machines for 15 years now and it's the only stuff that works properly. I've seen people use toluene, IPA, WD-40 & acetone. Of all these, only WD-40 doesn't attack the underlying surface in some way but it's incredibly messy.
My first computer was a TRS-80 Coco 1 with this keyboard but 64k w/64k badge. Got excited when I saw this as whenever I go looking for coco 1's they have the chicklet keyboard. :(
I love your channel. I saw it in my TV using an Android TV Box, so is impossible to do comments to your video. While watching this video on my tv, I'm writing this on my PC.
I had one of this CoCo, with chiclet keyboard and 16K RAM.
First that CoCo had all chips in sockets.
The 6809E CPU was a fairly easy chip to get.
The Williams arcade games of the era used that chip. So if you new someone who repair those arcade games, could give you some used chips.
The 6883 SAM Chip is another story. Is a custom made chip for these computers. And is almost impossible to find one in those days. I checked Jameco and other sellers of the era and no one had it.
The 6821 is a regular chip and could be obtained easily.
The 6822 is another custom made chip to handle the keyboard.
The ROMs are the Color Basic and The Extended Color Basic.
As you stated, both 6809 and 6883 chips are almost indestructible, but things happen. Specially because even with the computer turned off, there were power running in the board. So any mishap with all those cables could shorted both chips.
So far, I received 2 scam atempts via youtube's notification bell. One from TechLinked and the other was from AdamantIT. Of course, it's a scam and smells like one. I just ignore.
What is your lighting setup? Do you have a video on that on one of the channels? Consumer lamps or pro studio lights? High CRI LEDs? Halogens? Daylight colour temp or warmer? (funnily enough I started watching when you did bulb reviews) Thanks!
I used the color computers as machine very inexpensive controllers.
You could write a program in basic, do a few peaks and pokes, and gosub to transfer control to a plug in like a cartridge, that would run at full machine speed while in the subroutine. It wasn't hard to put a few 6522's and isolators on the external board to make it do whatever you wanted it to, and the pass the resultant data back to the basic program before you executed the return from subroutine and use basic to do all the graphs and calculations needed for the next gosub.
My friends all had Kaypros at work and would laugh at me for using the color computer, but they had no idea of the difference between REAL TIME DATA CAPTURES, AND SOFTWARE DATA CAPTURES, and were never able to get them to do much outside of the Kaypro box.
My only regret was that Radio Shack never came out with an 80 column version of it, and I had no access to enough information to make the changes to the basic roms that were in the machine to make that happen. I think that if they would have done that it might have cut into their TRS 80 sales, so it was probably a marketing decision.
Dennis O.
I did work experience at a TANDY store in the mid 80's - their list of technical books avaliable to buy was impressive .....
There is a replacement 6809E (6309E) that I suspect will work in all the CoCo computers. I don't know whether there are SAM replacements - CoCo people? Let us know!
I can remember back in the day I had an IBM PC, and a friend at work had a CoCo. Many of the young EE's at my employer had 'PC's because it had implemented a very generous loan program to buy them. We used to sneer at the Radio Shack computers. I had brought mine into work to do spread sheet and word processor work on it, but was showing off some game that played the William Tell Overture. "That's nothing" one of my office mates said, I'll bring in my CoCo tomorrow and show you what real computer sound is like. He did and blew my stock PC sound away.
I'm still waiting for the prize you told me I won. Let me know if you need more giftcards to cover shipping.
Thanks!
JK
"Human Malware" LOL... very good side stepping Adrian... Get well soon mate...
I think I got one of those scam messages but I lost it. Loving the TRS-80 information. Never had one myself but was always curious.
To answer your question on service manuals, the manual you pictured on your computer was actually sold in store - as was the manual for the Mod I. Service manuals for the other computers and most other items in the store were available through special order from National Parts.
Salesmakers might not have been aware of this. I found out through one of my customers at the time.
Anyway you could do a video where you network TRS 80 commodore 64 Atari 400 and a Macintosh computer
It amazes me how a 50 minute video can go so fast
Nice!
Just a small critique, it's a bit hard to follow which video is next in a "series", it requires some archaeology and clicking on different videos to get the next one.
I'm still uncertain as to which one is the next in this "series".
Maybe i'm just dumb, but i'm usually not.
Nice video thank you :) Hope you feel better now. I have had Covid for the past 10 days and whilst better now and negative, I am left with a horrible rattly chest and coughing up shite from time to time.
Onwards and upwards!
Maybe you could do a comparison video of the Dragon 32 vs the Coco?
Oh man, computers with schematics and theory of operation docs... Sure beats downloading board files from semi-sketchy websites
There is too much PSU components on the motherboard. In the Dragon this is a separate board. Also has an external AC output PSU. You don't want mains inside your computer. APC ATX do do this but the PSU is s sealed unit.
ribbon cables were the bane of my existence for a short time around 2000 . I stuffed up twice on my first day :P...I was used to normal pc's and was given laptops to fix..little did young me know how many ribbon cables could be possible back then - whoever thought they were a good idea needs binning :P
The SAM chip did create one clock signal. The other signal should be the same but slightly delayed. Try to make an external delay with a few NOT gates? Or a long wire (lo-tech). Check what offset the okay chip makes and replicate that.