Thanks! It was quite a challenge... really odd fault. Thanks so much for feeding back. Glad that you enjoyed the video

Thanks josh, so happy to be bring back fond memories (or frustrating ones LoL). Thanks for taking the time to comment. Sorry for the delay in responding

Awesome! Glad I was able to bring back some happy memories. I have a real soft spot for these machines. Great for developing my electronic repair skills, easy to repair using off the shelf parts and with a processor that is so flexible and easy to program. Thanks for your comments. Glad you enjoyed the video

@neb6 in my case the sun reduced the yellowing by several shades. It was quite impressive! I didn't video the process but I have photo documentation.

Thanks Vince!

Cheers Richard. Sorry that is been a while. Thanks for your continued support. Really appreciate the comments. Thanks so much

Awe thanks so much Norrectio that really means a lot. The troubleshooting was a bit of a challenge took me a long time in reality and along time to edit down to 20 min! I also checked all the connections against the schematic and checked the supply voltages to the chips but I forgot to include that! Anyhow glad that you enjoyed it and thanks so much for your kind words.

Hi Andrew. I had a zx spectrum probably around the same time but was a bit jealous of computers like this that looked like computers with proper keyboards. I've come to really appreciate the coco easy to repair with no custom chips and a great processor. I hope to bring another video on it at some point. Thanks for you comment glad I could bring back some memories

Hi Clarance yes I am and hopefully for a while, still slow to her vids out but hopefully better than before. Thank you for your patience.

Thanks so much. I am really grateful for the feedback. Sorry its been so long.

Roger goes the distance with these repairs. If you haven’t already; check out his laser disk repair video. It was a rollercoaster.

Thanks Stephen... bizarre isn't it! I guess the SAM does a lot of the heavy lifting in the architecture. Not sure. The CPU behaved quite differently in the Dragon. Still booted but crashed as soon as a key was pressed. Thanks for sticking with the vid to the end and for taking time to comment. Really appreciate it. Sorry its been so long.

That reminds me of the time our arcade museum's Q*Bert's sound board started acting up. The sounds were weird in a "the wrong sound is selected, probably a wire is broken" kind of way. Also whenever Q*Bert would start talking he never would stop until another sound effect using the SC-01 is played. And of course, when you turn on the machine, it says "Hello, I'm turned on". I changed all the chips in the sound line circuitry, made an LED debug cap I could piggyback onto the input latch to see if all sound lines get toggled, even made some kind of harness where you could manually select all the sounds. I eventually gave up. Then came the day when I had to test a 6502 CPU from a different machine and I used Q*Bert's speech board for that. All the sounds were correct. I put the original 6502 in my Commodore 8032SK - garbage screen. Another case of a broken CPU working well enough not to be suspicious. And just on this Friday evening I was working on an Atari Sprint 2, I removed one of the audio amps because it was very quiet and extremely hot. When I put it back, the machine stopped working. Long story short, the 6502's clock input became high impedance and I had to stack two identical logic ICs on top of the one creating the clock signal to get the clock signal back and the CPU works just fine! (I didn't have a spare 6502, but I had a bunch of 74xx32s used to create the CPU clock. With zero, there were just little spikes on the clock. With one piggyback, high was at around half a volt. With two piggybacks, it was a good TTL signal with high > 4V)

@@RetroTechRepair recently I’ve seen two instances on this happening. I think that the 6809E finally overheated and failed in this odd way. Weird.

Thanks so much. Really appreciate you sticking with me and taking the time to comment. Hope you enjoyed the vid.

Awesome! Thanks Ghost Retro. So pleased that toh enjoyed the video

Thanks telemedic. You may like the second video in this series. It looks at some of the very things you discussed. Great comments

Then you have been very patient. THANKS! I might do a channel update to explain at some point. Thanks so much for the feedback and continued support. Hope that you enjoyed the video

@@RetroTechRepair The video was great. I love this retro repair and you have a great way of troubleshooting and presenting it. Quality content for sure. Keep up the great work and know that you have fans out here always checking in for more content.

Thanks Brian thas genuinely lovely to hear. No other way to put it. Thank you

Thanks! You might like the second video in this series too!

That's what I thought. I'm guessing the cpu would have failed to run other stuff if in could have typed a command into it. Anyhow I'm very appreciative of your comments glad that you enjoyed the vid. Thanks for taking the time to comment.

Yeah.... the mc6821 and mc6822 are not 100% compatible I posted in the coco Facebook group for advice and everyone who commented dismissed my suggestion the 6821 would work assuming that to be the reason. Hope they watch the video. Thanks for your comment. Very much appreciate it

Yes it probably would be. I keep buying bits of test kit as I try to grow the channel. Maybe one day I'll be able to stretch to one. Thanks so much for your comments! Very much appreciated

Thanks MrVectrex. I think the piggybacking chips technique only works on some chips (eg, some RAM) as the chip needs to be of a type that has a high impedece state (tri-state logic high,low,high-z). If a "normal" logic chip fails the chip may drag a line high or low rather than go Into the high-impedence state that would be needed for pigging backing to work. Nice thinking though. Thanks for your comments (on this and my other vids).

Hi Brian, good thinking on the VCR. I can't say for sure what the keyboard problem is, mine has a membrane keyboard, not mechanical switches so I am not sure if contact cleaner would help. IF IT WERE MINE I would probably not apply contact leaner but look at either a membrane repair or replacement. My keyboard looks like the one shown here: www.leadedsolder.com/2020/02/02/coco-keyboard-membrane-repair-electric-paint.html I would probably also check the connections at the main PCB, shorting the appropriate ones together to see if the problem replicated (fault on main PCB) or did not (Fault on keyboard). None of this is advice, just what I might do if it were mine. Anything you did would be at your own risk. Thanks for your question. Good luck with the repair and thanks for your comment.

@@RetroTechRepair thanks much for the info. I’ll certainly look into it.

Hi there... I have a spectrum to repair but it's a rubber keyboard one. The +3 used an AY sound chip. Although I would like to get one someday. I have no experience and can't offer any help with your repair. Sorry

Oooh that's an interesting idea. Thanks for the suggestion. I didn't actually didn't know ow about that processor. Thanks so much for your comment

@@RetroTechRepair It offers a slight speed boost (almost imperceptible) and additional operations that new software is designed for taking advantage of. Canadian Retro recently did a video about whether it was a worthwhile upgrade and found a few reasons why it was. It’s easy to do in the CoCo 1 & 2 because they are usually socketed. I seem to remember there being a relatively easy composite mod also. I think several Tandy/CoCo enthusiasts channels have done this. Lastly, if you really want to go crazy, there’s a keyboard membrane swap that provides micro mechanical switches giving a more tactile feel.

@@jeffreyphipps1507 Thanks. Great info! Will definitely look into this. Thanks again.

@@jeffreyphipps1507 actually, with optimized code there is a significant speed boost. Without it, it's basically the stock CPU.

Thanks Wenlocktvdx... awesome info what great comment! I never thought about the audio sub-carrier freq. I have yet to edit up the second part to this vid so I will mention it then! Yes the artefact colours are great... really so much better than the PAL system. I honestly think that's what did for the Dragon 32. Artefacts were always the intention of the chipset, but only ever worked on NTSC systems leaving the PAL systems with a very limited pallet. Shame really the processor is a joy program compared to the 6502 and easier than even the z80. Lovely system. Anyway... glad I could bring back some fond memories. Tell or your friends... uptake has been a bit low on this one :). Thanks again for the very informative comments.

Trying to recall more about the PIAs. The 6822 could drive more load than the 6821 so it sounds like totem pole output versus open collector. The NTSC modulator has only 4mhz video bandwidth versus 6mhz with a UK modulator. Australia is in between with 5.5mhz sound and 5 MHz video bandwidth. Artifact colour was tried in PAL but it needed a change of pattern in the middle of the screen to have the same colour all the way across. Very few even used it. I used mine for things like slow scan TV thanks to Graficom, weather fax and even radioteletype (RTTY)

Hi @ms-ex8em, I am sorry but I don't know. I love these machines but mainly I am using original hardware (I have some Dragon 32 vids on my channel too). Sorry I cannot help but thanks for your questions. Hole that you enjoyed the video

I have to admit i haven't weighed it... interesting question though. 🤔 if I remember I'll pop it on the scales. Hope you enjoyed the video.

@@RetroTechRepair yes :).

Thanks Kenny