TRS-80 Coco 1 Repair and Mod -

I fix up the same computer model I used as a kid: The TRS-80 Color Computer which turned 40 this year. Watch me void the warranty :) on this never-opened Coco as I attempt to install a composite mod, fix up the keyboard, re-cap the motherboard, and clean it up.
Chapters:
00:00 - Intro
01:24 - Initial Testing
04:48 - Brief History
06:54 - Inside The Case
09:45 - Layout Of The Motherboard
15:17 - 64K or 32K
17:57 - Repairing The Keyboard
21:20 - Composite Mod Design
26:05 - Installing And Testing
33:33 - Re-capping The Motherboard
39:00 - Cleaning
42:25 - Final Thoughts And Wrap Up
Don't forget to check out all the other channels taking part in SepTandy:
Josh Malone: kzbin.info/door/jU4...
The Retro Channel: / theretrochannel
Adrian's Digital Basement: / adriansdigita. .
DaveJustDave: / mrdavejustdave
Jan Beta: / janbeta
MindFlareRetro: / mindflareretro
Tech Tangents: / akbkuku
Retro Spector: / retrospector78
LGR: / lazygamereviews
Disclaimer: Some links to buy products are affiliate links so I can raise support for the channel. This doesn’t affect the price you pay.
TheRetroChannel Coco1 Svideo Mod
• Tandy TRS-80 CoCo1 S-V...
I sometimes make my own T-shirts like the one I wore on the show
retrohackshack.com/shop/
Music used by permission:
“W.A.V.E.” by Emil Rottmayer
/ emil-rottmayer
“Rise And Shine” and “Fakebit World” by Malmen
/ malmen
Dragon 32 image - Rept0n1x / CC BY-SA (creativecommons.org/licenses/...)
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Website - retrohackshack.com
Tools I Use - retrohackshack.com/tools/

[@littlebiscuits]

That is the greatest t-shirt I have ever seen!

[@adriansdigitalbasement]

Love the meowing cat in the background. :-) I tried to do a Composite mode on my Coco 2 and it was a total failure, worse results even as you have to remove the RF modulator which contains that color encoder chip... The S-Video mod that Mark did on his Coco 1 looked awesome. Hasn't been tested on a NTSC model and of course you'll loose artifact color. I also have had an issue with IPA messing up paint on old machines. I no longer use it on computers and stick to windex, magic erasers for scuffs and WD-40 to get sticker residue off. 99% IPA is much more likely to cause damage but I think I've had problems with 70% as well. :-(

[@RetroHackShack]

Glad to know it's not just me :)

[@CoCoNutBob]

You should try brake parts cleaner. WARNING: Do NOT use brake parts cleaner anywhere near plastic! 🫣🤣 (I know someone who did this to a CD player and pretty much melted the plastic parts together.)

[@AaronHuslage]

You probably know this already, but for those that don't. The LCD panel understands pixels and the CRT understands lines of video. The panel in the LCD is trying to scale up NTSC RF scanlines into its square pixels and is having a hard time. The CRT is just outputting what it receives from the tuner more or less directly to the tube.

[@RobertEmery]

@@McFeedback1968 no, you can't. Edit: later coco2s (B models?) came with composite out, but RF out of an RF modulated CoCo requires a "demodulator" aka TV tuner. The CoCo plugs into the cable input, tuner must be set to *antenna,* not cable, and tune to ch3/4.

[@ChristopherWentling]

The magic of scan lines.

[@xeveniahdarkwind178]

Thanks for sharing this highly educational documentary.. the TRS-80 was the first computer that I experienced and started to form me into the I T Pro I am today

[@Oldcomputer]

Thank you for taking the time to show what is going on in the CC1 keyboard. I wasn't going to mess with mine because I expected it to be that cheesy carbon coated plastic deal other chicklet keyboards use. Now after cleaning mine like you did on yours it is working 100% better.

[@RetroHackShack]

You bet! Glad it helped. Sometimes it takes multiple rounds to get them all working again.

[@shawndavis5201]

When I was a kid, I had the F revision and easily upgraded to 64K. Just installed the new RAM, added a jumper, and cut the capacitor located at the bottom of each RAM chip socket. I remember taking my CoCo to Radio Shack to have the Extended Basic ROM installed for $100. The local store sent the computer to Texas to have the upgrade performed. Got my machine back in about 2 weeks. That was the longest 2 weeks of my life back then. I did the memory upgrade myself after that.

[@RetroHackShack]

Love it! Thanks for sharing that story :)

[@CurtisBoyle]

Great video! (and I have seen you on TWiT many times, including with your Dungeons of Daggorath shirt). And yes, they restarted serial numbers at times. (I think yours is an E Board; there are a very few C boards in the wild, then D and F revision motherboards as well). I can't quite read it, but there is a number on the right side (just below the cartridge port) that will have a number "-E" (which indicates an E revision motherboard). I should mention that in practice, most of the 64K chips used were fine with the full 64K. You can address it all, with a very slight mod (you can address it two ways; map all 64K in at once (shutting off the ROM's), or swapping 32K RAM banks in the lower 32K, while leaving the ROM's turned on. Also, if you want to see all of the magazines, and software (both from back in the day, and new), please pop by the Color Computer Archive (www.colorcomputerarchive.com). Also, we would love to have you on our live CocoTalk show some time (recorded every Saturday at 2 PM; lasts for several hours, so even if you could pop in for a small amount of time for an interview, and to promote your current stuff, that would be awesome). You can see some past episodes here: kzbin.info/aero/PLDfh7JjQaSYC1p7sxFIm4i8HU7-Yj0ssB (If you are interested, please send me an email at [e-mail]). The general page is at: cocotalk.live. Also, if you get a chance in the future to swing by the TWiT studios again (probably not possible in the immediate future?), maybe hit up Leo a few days early to borrow his copy of "Coco: The Colorful History of Tandy's Underdog Computer", which is very well researched history of the entire Coco line, including interviews from some of the principals from Tandy from that time period.

[@RetroHackShack]

Ha. Glad you noticed that shirt! I finally put it up to order. And yes. It is an E. I forgot to mention it later.

[@MarceloReis1]

My very first computer ❤️ Amazing how much could be done with it!

[@StuartCowan]

Really enjoyed your video, I've been trying to get good composite video from my machine and failed so it's been really useful to see your attempts too.

[@RetroHackShack]

Glad it's not just me :)

[@StuartCowan]

@@RetroHackShack Cool, Had another go and managed to get a good result, removed the modulator internals and simply used a 100uf smoothing capacitor. Added an audio out jack and installed it all in the case of the rf modulator. Results on my instagram feed @kpdcowan

[@RetroHackShack]

@@StuartCowan I will take a look.

[@PJBonoVox]

Hey man. Enjoying the video. Your cadence and editing is top notch, and I hope you find the wider audience that you deserve.

[@RetroHackShack]

I appreciate that!

[@gdajer80]

I followed your tutorial and my keyboard is working again like brand new! Thanks

[@RetroHackShack]

Awesome!

[@SixOThree]

I remember buying EDTASM+ with $70 worth of loose change I had collected. The people at radio shack were understanding.

[@srh76able]

G'day from Australia! i just saw your comment on another channel and thought I'd drop in. Keep up the good work!

[@RetroHackShack]

Thanks for the support!

[@dLLund]

thank you for posting. i paused & subbed at about 19:00 when you said 'get ready for unscrewing montage'. if i were uncouth, i'd make a remark about memories of prom night. luckily, i'm very couth. take care & stay safe.

[@RetroHackShack]

I think I made another unintentional innuendo in my Atari 7800 Composite Mod video. Something about not passing up a perfectly good hole. *face palm*

[@BenevolentChum]

Nice Vid. Now do some TRS-80 MC-10 stuff;)

[@konturgestalter]

love your channel!

[@RetroHackShack]

Glad you enjoy it!

[@vhm14u2c]

Thanks for sharing!

[@rivards1]

Great new channel! Subscribed.

[@RetroHackShack]

Thanks for subbing

[@MattSiegel]

that t-shirt is amazing :D

[@cbmeeks]

Great video. Things happen. I've messed up cases too. Like the time I accidentally got acetone on my C128D external keyboard (which are rare) and it melted the plastic. Once you pass that "uh oh" stage...may as well paint it. Watch Retro Man Cave's video on stripping and painting a Model 1 TRS-80. Lots of good tips there.

[@RetroHackShack]

Hmm. I must have missed that one. I will check it out. "Uh oh stage" describes it exactly. I wish I was recording at that point.

[@TheRetroChannel]

Good job on the video, kept me watching. I was going to see if Mr Lurch wanted to add your video to the SepTandy playlist but it looks like he's already done it. Also thanks for the shout-out, interesting to see your results with the composite mods. From what I have heard it seems nobody has really been happy with the results vs RF. Hence my S-Video mod, which also took me way too long but for me at least it produced an output I'm happy with. Just gotta wait and see how others go with it, so give it a try if you want. Shame about the IPA eating the paint, I'll be sure to avoid doing the same.

[@RetroHackShack]

Thanks! It was pretty funny that your video came out just as I was about to give up after my first attempt failed. That led me to try a few more things.

[@tenminutetokyo2643]

Also replace the 2 small DC regulators with modern switching ones. Shrinks everything and you can dump the heat sinks.

[@enjoythepig]

Great video. My coco1 is a rev f, with 16k. It had a sharpie marking under the top of the case of 10/22/80. The F allows you to upgrade to 64k by just adding the chips and a couple other easy mods. Also the chips are all socketed on mine, including the CPU and SAM. The RF cover is also a lot smaller, not covering the CPU or SAM, and you can only remove it by straghtening tabs on the bottom of the board. I also noticed that your tag is black, as is mine, but another machine I got recently with the extended basic chip, also has a rev F board, and the tag on the bottom was purple.

[@RetroHackShack]

It seems like there are so many versions of marketing that Tandy/RS was putting out back then. I have seen multiple versions of the same disk or cartridge that say Tandy or Radio Shack, but were seemingly released at nearly the same time. :)

[@ragsixracing]

Haha. I remember a friend and I putting a pause toggle switch in my coco. I believe it was pins 4 and 11 on the cartridge port. It would pause everything but the loading of programs. I got much enjoyment from this computer and still miss it.

[@RetroHackShack]

Cool!

[@Luis45ccs]

Incredible flannel with led as a coco cursor. I seem to remember that for the conversion to composite video to work correctly, you have to remove or disconnect the RF box or it will interfere

[@RetroHackShack]

Hmm. I might try that with the next one.

[@CoCoNutBob]

@@RetroHackShack I am struggling with this same problem. My white case CoCo 1 had an aftermarket composite mod from the 80s that threw the artifact colors off. 🫤 I simplified it to the basic circuit you're using, and it's better, but I want to remove the RF can to see if it gets better. Now the composite out has correct colors but the RF is out of phase..? Sheesh. Doing this in my silver case, restored the white case to original.

[@hammathguy3995]

That's odd. I seem to remember that mod working quite well for me. Of course, that was nigh on to 40 years ago. And, I was was using a bodged TV that I bypassed the RF circuits and directly drove the video de-modulator. Those were the days.

[@RetroHackShack]

I am going to give it another try in an upcoming episode.

[@monomonster]

My first CoCo was a CoCo1 'C'-board. ECB 1.0, and 16k of ram.

[@KarlKranich]

This was my first computer too! I was surprised that this one didn't have the "badge" showing how much RAM it has. Mine had the "4K" badge and I upgraded it to 32k/64k.

[@sideburn]

Going ahead with extended color basic!

[@johanlaurasia]

Actually manufacturing processes quickly made "half bad" chips increasingly rare, so most "32k" machines actually have "all good" 64k chips in them, even though they were sold as 32k machines. Once the CoCo 2 was out, they began referring to them as 64k machines.

[@jameslewis2635]

Interesting point on the memory. I believe that something similar was done with the Sinclair ZX Spectrum. I don't think we ever got the TRS-80 here in the UK, at least not in any apreciable numbers but as I understand things the cost of these machines was their downfall. It does seem to be a bit odd that a lot of home computers from the 8/16 bit era seem to have these faraday cages tacked on to their designs a bit like they were not expecting to have to comply with these rules. As yet, I have not found a computer that actually needed these shielding but if the manufacturers knew they would have to shield the systems, wouldn't it have been better for them to have used a metal casing and stand-offs rather than some weird cardboard & tin foil arrangement.

[@ReverendLinc]

Always use WD40 to remove sticker residue, Aaron. Works fantastic!

[@RetroHackShack]

It's on my bench :)

[@tomlindo2863]

I know that the paint on the silver cocos are some soft paint that loves to come off. I think WD40 would be fine but personally you'd be hard pressed to get me to use anything more then water and maybe windex. Certainly would test on the bottom first.

[@RetroHackShack]

@@tomlindo2863 Goo Gone also seems to take off a little paint, but not nearly as bad as IPA. I tested that on the back :)

[@loganjorgensen]

Composite is generally bad on LCDs from a lack of true 240p support, a lot of them tend to do a sloppy convert to 480p but it adds interlace artifacts as a side effect. Went and got a RetroTink-2X Pro since the new TV didn't have any legacy ports, this upscales 240p to a cleaner native 480p signal modern screens understand. 2X-Mini is a bit cheaper but only goes as high as S-Video.

[@tenminutetokyo2643]

What did you replace the relay with?

[@JamesBond-qv2ht]

I am trying to diagnose a keyboard issue on a Coco 1 computer and hope you can help. Certain keys don't work and after looking at a schematic, I see that they are all associated with a particular pin on the keyboard connector. I tested continuity between the beginning of the keyboard ribbon cable and the relevant pin on the MC6822P chip and it is fine. Is it likely that since I don't have a bad connection, the chip is bad? If the chip is bad, do I need one specifically programmed for the Coco Model 1 or will any MC6822P chip due? I want to save this computer from the trash heap, so your thoughts are much appreciated.

[@RetroHackShack]

Could be the chip. Did you test the continuity on the switches themselves?

[@JamesBond-qv2ht]

@@RetroHackShack it is an aftermarket keyboard that is hot glued in place, so no. I may do some surgery and test the keyboard especially since replacement chips seem scarce unless I want to buy an entire computer.

[@jasondowns2778]

That board will happily address the full 64k if you add the missing decoding logic. Instructions are in the document you showed, they work fine.

[@BigBaddaBoom]

@22:21 That AMDISK-III, I have never seen one of those before. I guess it must have failed as a product. But, it almost looks like it is in the wrong time.

[@marknichols7861]

Try using Rosonol Lighter Fluid as a sticker goo remover. I've found that it appears to be safe for most everything and removes the goo remarkably fast and completely.

[@RetroHackShack]

Does it leave a smell though?

[@marknichols7861]

@@RetroHackShack not that I've noticed. I've used it on convertible top windows too.

[@RetroHackShack]

I'll pick some up and give it a try

[@GORF_EMPIRE]

I can tell you that if you shorten and shield those wires to the mod as short as you can, you should get a much cleaner output.

[@xeveniahdarkwind178]

I think you may want to consider consulting Texas Instruments.. they did lots of Manufacturing for Tandy RadioShack aka TRS

[@lexpee]

The best output is an RGB Signal. I don't know if this is also possible with this Tandy computer.

[@relo999]

no, it aint

[@loganjorgensen]

I've noticed silver paint on plastic often comes off with IPA. I tend to use Hydrogen Peroxide on things that might color bleed.

[@RetroHackShack]

Interesting. That is the first time I have heard about Hydrogen Peroxide. I might have to test that out.

[@loganjorgensen]

@@RetroHackShack Doesn't evaporate like IPA so you just moisten your towel, clean, and wipe off any left afterwards. Had many things like sticker labels that IPA would ruin but still had dirt on them so I needed something more gentle.

[@DaiAtlus79]

43:13 it's the kind of plastic paint they used, u need denatured alcohol (essentially moonshine or everclear) which is much safer on plastics. isopropyl is much more caustic to plastics like acrylic

[@RetroHackShack]

Hmm. I will have to test that out on a scrap item and see how it works.

[@knghtbrd]

I wonder if your composite mod would've worled better with a shielded or twisted composite video wire. The reason for that obnoxious RF shield is that nearby wires, particularly unshielded ones, might pick up hash from the system. your run was certainly long enough to do that. I can say I _wish_ my RF out looked like yours. it definitely does not. Your worst result looks better than the best I've got.

[@RetroHackShack]

I was using a shielded cable for some of the time.

[@Phantom8Bit]

Radio Shack seems to have restarted serial numbers with new model numbers

[@ingmarm8858]

I see you have a USB oscilloscope on your wall in the workshop so I'd suggest you look at your composite video out when plugged into a SINGLE load i.e. one monitor. The input impedance of the video inputs on the monitor/TV should be about 75 ohms, with that load your composite video signal should be ~1V from bottom of sync pulses to the top of the whites. Of that the video makes up 0.7v and the syncs 0.3v (look at any reference image on google). If your levels are way too high or low (including the ration of video to syncs) then you will likely see crappy image quality. That would be the likely reason you are seeing better modulated RF video than straight video.

[@RetroHackShack]

Awesome suggestion! I did that, but didn't show it on the video. This scope is kind of crappy, so it was hard to see the levels precisely enough. Perhaps I will put this in the video next time if it is interesting to people.

[@twistedyogert]

I want to know how to control an external device using a COCO.

[@RetroHackShack]

What kind of device?

[@lelandclayton5462]

You would of probably had better results if you used shielded cable for the Composite wiring. Typically I will use an old Component Cable or RCA cable for that sort of thing.

[@RetroHackShack]

It's a good tip. I tried both shielded and unshielded but didn't mention it in the video.

[@anjinmiura6708]

Weird how you had two Ws

[@RetroHackShack]

Ha ha. It's been I while since I looked at this video. I had forgotten about that.

[@tolkienfan1972]

I think the issue with composite is with the crt tv itself.

[@RetroHackShack]

That is definitely part of it. I am just working on a follow-up to this video where I get HDMI out that works really well.

[@tolkienfan1972]

@@RetroHackShack awesome. Can't wait to see it. I'm very tempted to try to restore some old hobby computers myself. Looks like a blast. A frustrating blast!!

[@tolkienfan1972]

@@RetroHackShack also, wish I had kept my TRS-80s when I left the UK for the US.

[@tolkienfan1972]

@@RetroHackShack I guess the impedance could change if you don't disconnect the included modulator.

[@RetroHackShack]

@@tolkienfan1972 Yeah. That's a good point and something I always forget to take into account.