Tandy TRS-80 CoCo1 S-Video / composite mod

UPDATE: Check out the new and improved S-Video mod: • Simple Tandy Color Com...
As part of #SepTandy 2020 we attempt to upgrade a Radioshack/Tandy Color Computer 1 with S-Video and composite video, all while keeping the original case untouched.
This was all done on a small piece of perf board, the S-Video and TRRS connectors are ones I had on hand so I don't know what the part numbers are for them - they took a bit of hacking to fit on the perf board, so probably wouldn't help to list them anyway.
🛍️ Tindie store: www.tindie.com/stores/theretr...
🛠 Tools and kit: / tools-and-kit-77570017
💬 Discord: / discord
😎 Ad-free, early access: / theretrochannel
🎞
0:00 Intro
0:46 What’s a CoCo?
2:56 The plan
4:21 Installation/removal
8:14 Test fit
11:36 More info on the mod
13:40 Soldering it in
16:46 Time to try it out
18:42 Comparison shots
22:20 Stuff
🎞
🔗
Be sure to check out all the #SepTandy 2020 participating channels:
Mr Lurch's Things: / mrlurchsthings
Josh Malone: / joshmalone_48kram
Adrian's Digital Basement: / adriansdigitalbasement
DaveJustDave: / mrdavejustdave
Jan Beta: / janbeta
MindFlareRetro: / mindflareretro
Tech Tangents: / akbkuku
Retro Spector: / retrospector78
LGR: / lazygamereviews
SepTandy 2020 playlist (keep checking for updates): bit.ly/septandy2020
The schematic for the S-VIDEO mod: imgur.com/a/bxymQxO
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Thanks for watching!
#SepTandy #TRS-80 #CoCo

[@TheRetroChannel]

UPDATE: I've since created a new and much more simplified mod here: kzbin.info/www/bejne/pXiclaulZ8xpitE

[@OzRetrocomp]

"I've got a lovely bunch of CoCo-1s" should be the SepTandy theme song. :D Great video, and definitely something to keep in mind when/if I add a CoCo-1 to the collection.

[@TheRetroChannel]

Bah, of course. I had coco-nuts stuck in my head, coco-1s is much better

[@39Chevy]

Excellent video. Love the format, the lower key humor, great stuff.

[@RetrogradeScene]

Love the out takes! Great job nice to learn about the TRS-80 I've not had much experience playing with them!

[@bornach]

Nice. That's my Dad's first 8-bit computer that I used to learn how to program in BASIC and assembler. Probably ruining my eyesight in the process.

[@jeffreyphipps1507]

I was subscribed, but missed going back to watch (busy month). S-Video was awesome. I was sitting then imagined being a time traveler and grabbing a Coco user and bringing him to see the "same" machine, only with a flat panel and a crisp display and no floppy drive. It would be so trippy for that person....

[@TheRetroChannel]

Hey Jeffrey, yeah it would be pretty mind-blowing to see something like that back then. What's funny is a lot of these systems actually have video formats that are somewhat compatible with what later became standards, like S-video and component (YPbPr). I guess it's just there's was no real reason to make them available to the end user as RF was simple, cheap and commonplace. Especially for households in the late 70s, early 80s

[@jeffreyphipps1507]

@@TheRetroChannel Yeah, although composite had existed since the mid 1950’s I doubt that most TVs bothered with it. I don’t remember any of the TVs of the 1970’s or even the early 1980’s coming with composite. When cable TV first came through it connected with coax to new TVs and used baluns to connect via older connections. When hobbyists wanted better video, we first found monochrome terminals, then adapted them as monitors. We then stripped RF down to composite signals. When color tubes came into existence, they operated with RGB and added circuits to minimize wires. Composite needed splitting out at the TV/monitor. Then we accepted the wires and used component with less multiplexing. As we moved into digital this just became easier. Had we been using digital RF sooner, we might still be using it today. Most of our inventions are more evolutionary than revolutionary because upsetting the apple cart doesn’t sell. Gradually changing things when clear superiority exists is easy to sell. Early adopters pay the way for reduced production costs and works out the bugs. Same for any tech or any product tech or not really. REALLY liked the S-Video mod and how it was non-destructive to the case. Very nice and high quality improvement. Can’t wait to see what the problems were with #2 (playing catch up here). Binge watching these. Enjoying them. Thanks!

[@dLLund]

thank you for posting. subbed. please take care & stay safe.

[@acs8-bitzone651]

Hello TheRetroChannel ! I saw your CoCo 1 video while I was working on the S-Video mod! It was fortuitous and I learned plenty from yours, believe me. That is the cool thing about having all these interesting channels like yours to view; there is something to learn everyday. About the variable resistor you are needing to add in series with the Chroma output. I'm not familiar enough with every S-Video variation that monitors and devices have implemented so I don't know the cause of this issue yet. But I noticed that in the bhabbott.net.nz reference that I showed in my video, that he had an AC-coupling capacitor in series with his 75-Ohm Chroma output. I didn't know why it was there, and I haven't seen it in other implementations. My guess is that some monitor inputs do not tolerate as much common mode voltage offset, or DC offset, and want the signal closer to ground. Did you discover that your FrameMeister needed 1k by experimentation or did its documentation cover it? The 1k would attenuate the voltage level, but I wonder if the AC coupling cap would also have worked. It wouldn't attenuate, but it would shift the common mode voltage closer to the monitor input.

[@TheRetroChannel]

For anyone interested, AC also created his own S-Video mod. You can find the video and my response to this question there kzbin.info/www/bejne/qpLceKawbL2maaM

[@uni-byte]

Nice job. Just a suggestion, but I would have used wire-wrap wire and run it through one or more of the RF modulator mounting holes, or a strategically drilled hole, to the underside and attached to the IC pads down there. Purely cosmetic... I 'm interested in doing this to my COCO-1, but it's a pristine example and I'm a little reluctant. Love COCO's though. I have a 1, a 2 and a 3 as well as an MC-10, if you can call that a COCO.

[@TheRetroChannel]

Thanks, and yes I definitely considered doing the wiring from the underside and brining it up through the RF mounting holes. I figure the design will be tweaked at some point so it will likely be coming back out again

[@kennethlonnberg5817]

This is my first comment ever on KZbin but only because I haven't been able to find any other method of contacting the creator of this channel so I really hope he reads this. Anyway, I just wanted to say that the S-video/composite mod featured in this video has found a use in a rare video game console called the Gakken Compact Vision TV-Boy. I recently managed to acquire one of these for my collection and due to its rarity extremely little information is available. However, when I started digging around in it I noticed that it shares the same MC1372 and MC6847 chips as the Coco and I figured I might be able to use this mod in the console. Sure enough, it actually does work, though I suspect it needs to be optimized for the TV-boy in order for the best result. Still, it's a huge improvement compared to the stock Japanese NTSC RF output, though some TVs doesn't seem to like the signal.

[@TheRetroChannel]

Hey Kenneth, glad it (sort of) worked for you. Very interesting to hear about this Gakken tv boy, I just googled it - the joystick reminds me of an 80s automatic gear shifter! Anyway, as I assume it's an NTSC machine you may want to try out the S-Video mod by AC's 8bit zone kzbin.info/www/bejne/qpLceKawbL2maaM He shows his circuit around the 50 minute mark in the video. I built his design yesterday but i still had trouble with the chroma, so I had to put in a potentiometer to adjust the chroma levels. But I think that chroma problem is limited to PAL machines so you may have better luck with his design. Cheers

[@DaveJustDave]

great job! I almost want a coco1 now.. almost. :)

[@TheRetroChannel]

Haha, yeah it's almost worthy

[@johanlaurasia]

Nice S-Video Mod...

[@toyra]

Watched alot of your videos but always forgot to subscribe :( But Subscribed now :)

[@MindFlareRetro]

First! Haha! Awesome video! And timely -- I've researching better video output options for the NTSC CoCo 2 I'm working on, so this was very interesting. I do like the S-Video option, but I am not sure if that is easily doable on a CoCo 2. Your perfboard circuit worked really well IMO and the fit was brilliant. Has anyone laid that out for making PCBs -- perhaps a KiCad project for you? Anyway, this is another great #SEPTANDY contribution. Well done! Oh! And thanks so much for the extra shoutout; that made me laugh.😂☕

[@TheRetroChannel]

🏆

[@MindFlareRetro]

@@TheRetroChannel I did add a more substantial comment. I just wanted to be *first* for once! 😜

[@TheRetroChannel]

Thanks MFR, maybe with a bit more testing it could become a proper PCB. I really want to sort out the sync issue. I know most people probably use the same display, but having to potentially open the computer to adjust that trimpot when changing displays is a pain in the arse. I guess there's always the composite out as a fall back, but who wants that when you've got S-Video right there

[@TheRetroChannel]

The 1372 can drive the circuit from its 5v supply. I would recommend trying out the mod by ACs 8bit zone, you can find it here: kzbin.info/www/bejne/qpLceKawbL2maaM He talks about it around the 45 minute mark and there's a link in his video description to his circuit. Like I said, circuit design is not my strong suit and he clearly knows a little more on the subject. If you have a PAL machine then either circuit may not work reliably, unfortunately this is just due to how the signals are created in the PAL variants. But if you have NTSC then definitely try ACs mod

[@captaincorleone7088]

Nice video: subscribed! :)

[@2010Thex]

Great video!!! I saw Adrian Digotal Basement where he modified the RF modulator to do composite out. Wouldn't that work on your Coco computer?

[@TheRetroChannel]

I know the video you're referring to, but it wouldn't really work with the CoCo. And even if you did manage to convert the RF to composite, you would still need to add another socket for the audio out. It would be nice though

[@RetroHackShack]

The one where you snip the wire on the composite input to the RF modulator like you can on the Spectrum and feed it directly to the video jack? Short answer seems to be YES! I just tested it and it seems to work. I am working on a similar video and I am drooling over the quality of this svideo output. So far I have tested three different composite mods, but the best output I am getting is by just tapping in to pin 1 on the RF modulator for composite video and pin 3 for audio. Still, the composite output is not as clean and bright as I would expect. I am going to try replacing some caps and see if I am just battling some interference that isn't getting filtered out.

[@TheRetroChannel]

Looks like the YT spam filter held your reply, funny since it's more than happy to let through the "Let's be youtube friends" spambots. Anyway, yes you can tap the video off pin 1 and audio off pin 3 of the RF modulator but they will not be very "clean" and I'm pretty sure the video signal has a pretty large DC offset. This may be confusing your display by not being able interpret the correct reference black/white levels, causing too dark/bright/low contrast output

[@adriansdigitalbasement]

The S-Video does look pretty great! Ok I need to try this -- but the issue is the Coco 2 I have has the encoder chip in the RF modulator. So I assume I will need to keep it inside there? Maybe?

[@TheRetroChannel]

Yeah, that's the tricky part. I also tested it with the CoCo2 but again the PAL version I have has the 1372 outside the modulator. Still I think it's worth just trying to tap off the 1372 while it's in the modulator and see what you get. Just throw everything on a little breadboard and probably check the output on your scope before connecting it to a display, just in case

[@ownpj]

Given the proximity of the chip you're pulling signals from, design a drop in board that sits over the chip socket and has passthrough legs. That wsy you only have the audio lead to solder separately.

[@TheRetroChannel]

Good idea Peter. This is very much in the prototype stage, so there's a few tweaks to be made

[@IrishCarney]

Can anyone do a mod that lets a CoCo3 handle artifact colors and be fully compatible with semi-graphics mode?

[@themanwithnoname8241]

I like composted video 😊😁🤔

[@WolfKenneth]

Do month for Amstrad/Sinclair!

[@TheRetroChannel]

There was a little riffing amongst the SepTandy group about other months. I believe JanStrad was thrown out there. Sinclair is a bit harder, maybe AugusTrum, NovemClair?

[@WolfKenneth]

@@TheRetroChannel JanStrad sounds cool. This will probably anger many speccy fans but I think Amstrad and Sinclair should go togheter after all it was bought out by Amstrad and theres not many pure Sinclair machines. Other option is doing only Speccy month with all the clones out there all around globe :)

[@mikeme9938]

Don't you kinda find it refreshing to work on a system that is fairly trouble free compared to a C64?

[@David_Ladd]

Do you think your PCB design for the S-Video work on the CoCo 2's? Also not sure if you know about CoCo Talk or not, but you can find a link here: cocotalk.live/ A video talk show about the Tandy Radio Shack Color Computers.

[@TheRetroChannel]

Thanks for the link David I'll check it out. I'm not sure if it it will work with the CoCo2. I've already had a few people ask the same thing so it's definitely something to test out when I get a chance

[@David_Ladd]

@@TheRetroChannel , your channel came up in our news discussions today and I figured I would let you know about our video talk show. Plus we have a Discord server where we normally hang out if you like to join. If interested.

[@TheRetroChannel]

@@David_Ladd I just had a look at a bit the replay, very cool. As you can imagine this month I'll have little free time but I'll be sure to catch up with you guys in the near future. Cheers

[@David_Ladd]

@@TheRetroChannel , That is great :) Hopefully this month goes well for all of the streamers doing the #SepTandy

[@Ballowax]

Why are PAL artifacts so bad with composite video

[@TheRetroChannel]

Its just due to how the PAL system encodes colour information. As most CoCo games were developed in the US they were designed to take advantage of this hack, which worked fine in NTSC (apart from occasionally having the reset the machine to swap the colours being displayed) but PAL can't do that trick and so we ended up with purple and green stripes 🤮