TRS-80 CoCo1 - A look inside the heavily modded CoCo

[@CurtisBoyle]

Try SHIFT-0 to switch between upper/lowercase (or upper regular/upper inverted, depending on your one switch). Note that BASIC has no idea what to do with anything but the default case, as far as keywords go. As you figured out, the lowercase kits were basically ROM images of character sets (which is why you have an EPROM on your satellite board); so that one switch tells the 6847 VDG to switch from it's internal (inverse video for lowercase) character set, and from an external ROM (the true lowercase one on the EPROM chip). Great video!

[@TheRetroChannel]

Thanks Curtis, I think I've figured out how it all works now after putting it in the other CoCo. But interesting to hear more detail about it. Do you know if these were fairly common?

[@briangoldberg4439]

Interesting. Looking forward to the seeing your troubleshooting.

[@MindFlareRetro]

Man, I'm glad I'm not the only one feeling the CoCo repair noob growing pains. This is a lovely computer, but those mods, especially the lowercase mod ... fun to do back in the day, but what's the point if you can't mix upper and lowercase text. Looking forward to the troubleshooting episode -- I must learn more! Great work again!👍

[@spargerful]

It's been 40 years, but I think that board is an LCA-47(????) lowercase mod from.....microtech? Tho, I think that just has two switches...one for lower case and the second to invert the colors on the screen. It's been a while, though, so take that with a grain of salt.

[@TheRetroChannel]

Thanks Arne, yeah the switch configuration is a bit odd. There will be a better explanation in the next video

[@ChristopherNelson2k]

Was totally not prepared for that clip @21:46!

[@TheRetroChannel]

🙊

[@PeterRidge]

Thanks for the info on the keyboard. My Coco1 has the same upgrade, which I purchased at a Radio Shack long, long ago. I'll have to see if it's an HJL or just a lookalike.

[@parrottm76262]

Oh, we have a mystery! I'm intrigued.

[@MikeDancy]

Dude! Where have you been all my life? What a great machine. I own two of them - that would look better on a CRT

[@TheRetroChannel]

Everything looks better on a CRT 😁

[@CRTWorlds]

Good luck with this one. It came to the right place, tho. I wouldn't even know where to start with fixing it. Great vid! I subscribed!

[@JavisoGaming]

WoW! I had a CoCo1!

[@Retrospectreviews]

Nice video

[@johanlaurasia]

In it's highest mode (256x192x2), it had black and white, but alternating black/white and white/black dots would produce a red or blue color. What color you got relied on weather the color signal was syncing to the rising or falling ramp of the color signal. This artifacting was commonly used to create a 4 color mode in the 2 color high resolution mode giving red/blue/black/white. You'd commonly have to hammer the reset over and over until a particular box turned red or blue, then proceed to the game (but actually you could just ask the user what they saw and adjusted how you obtained your colors based on that). In any case, it's pretty clear switch 2 is forcing the ramp one way or the other (something built into the color computer 3, holding down F1 while turning on would force the color one way, turn it on without holding any key would force the other.

[@TheRetroChannel]

I've read about this and certainly in NTSC machines this has its advantages, but on PAL machines this trick looks like arse either way. There's a comparison of both in the first video

[@johanlaurasia]

@@TheRetroChannel Yeah, agreed, it's definitely an NTSC quirk, and yeah, on PAL I'm pretty sure it looks horrible. The CoCo wasn't particularly popular across the pond, but the Dragon, which was essentially the same Motorola reference design with their own ROM, but I'm not sure how things worked in the higher resolution modes on those devices, which, aside from the ROMs were very close to the CoCo in design. Anyway #SepTandy is turning me on to some new retro channels including yours. Like what I see so far (sub'd!)

[@rog2224]

14:30 ish - that was almost archaeology.

[@MrLurchsThings]

The lowercase and font mods seem kinda pointless if it just forces it. There has to be more to it. But man, yeah. Even composite is terrible on these Coco 1’s. Admittedly I haven’t even tried composite on my 3.

[@johanlaurasia]

FYI to both Mr Lurch & TheRetroChannel, there's a mod out there called cocoVGA that adds several graphics modes plus outputs via an S-Video connector to a cable that has a standard VGA connector on the other end and will output perfect crisp video to a VGA monitor. I believe it works ok on PAL systems, but there's an issue because PAL systems locate the VDG in an odd spot making putting the case back together an issue, but it's certainly worth checking out... cocovga.com

[@TheRetroChannel]

@@johanlaurasia Thanks John, yes Jason actually pointed my towards the cocovga before we started SepTandy this year as I was whinging about the video output from RF and from the fairly common composite mod. And although I considered the cocovga, I wanted to see what was possible with a handful of passive components, and voila - S-Video

[@johanlaurasia]

@@TheRetroChannel Yes, that's an impressive mod considering it was your own roll your own solution, and it works very nice! Will also serve the community well as I'm sure it's way cheaper than CoCoVGA, and cost is a consideration for many. I did a video where I fixed a bad ram chip and installed cocovga.

[@davidkroeker1821]

Composite output on a stock CoCo3 looks pretty bad as well. The CoCo3 RGB output is vastly superior! Commodore did a much better job with composite output, for example. Being a CoCo3 owner who uses both RGB and composite (for NTSC artifact colours) outputs with a Magnavox 8CM515 monitor, I'm interested in Svideo/composite mods for a CoCo3.

[@TheRetroChannel]

Nice, I'll check your channel.

[@joelavcoco]

I wonder if that lowercase mod was a Green Mountain Micro (Dennis Kitsz) Lowerkit.

[@TheRetroChannel]

Ahh interesting, that could be it. I will do some research and hopefully have some more details by the time the next video is ready

[@richardadams4928]

Ah, Dennis Kitsz. I was an UnderColour subscriber and talked to Dennis on the phone once. Nice guy. Wonder if he ever finished his Elisabeth Bathory opera?

[@johanlaurasia]

The 3rd switch looks like it's swapping which ramp the color is syncing to (rising or falling), which affects red/blue in the false 4 color mode (actual 2 color mode). Looks like switch 1 is (trying?) to switch between black on green / green on black (inverse), obviously switch 2 is enabling/forcing the lower case.

[@TheRetroChannel]

Yeah, I've tested it out in the fully working CoCo1 and you're very close. If I can't get this CoCo working properly then I'll use the working one to demonstrate what they're supposed to do

[@CyBeRTRoNFLuX]

hahahahaha ohh man i love that shirt !!!!!!!

[@monchiabbad]

You forgot to add #septandy to this clip.

[@TheRetroChannel]

Thanks, updated