Icky made me do it - TRS-80 CoCo

[rubber_jonnie]

Ahh, that's better 😁

IMG20240218170814.jpg

Just need to test audio now.

[stephen_usher]

It is easier to read, indeed.

[rubber_jonnie]

It is easier to read, indeed.

Hopefully I won't confuse anybody, as the machine in shot is the TRS-80 Model 1 and it isn't switched on and certainly doesn't have colour basic :)

:dizzy:

Only problem now is audio, in that it's dead silent. However everything is easily accessible from the top of the PCB, so I've chucked it together so I can spend some time with the C128, and I'll come back to the audio later.

[rubber_jonnie]

Oh good, just looked up the RAM in this machine and it's basically the same as 4116 with +5v, -5V and +12v.

Going to have to get creative with some 4164's I think.

[alexh]

Nice. I've never owned one. CoCo was the first computer I saw reproduced in an FPGA shortly before MiniMig was released.

Did anyone here use a CoCo scandoubler with their Atari ST? I did.

http://www.miba51.com/CoCo_VGA_Adpater.html

[rubber_jonnie]

Nice. I've never owned one. CoCo was the first computer I saw reproduced in an FPGA shortly before MiniMig was released.

Did anyone here use a CoCo scandoubler with their Atari ST? I did.

http://www.miba51.com/CoCo_VGA_Adpater.html

It's a pretty simple machine, just about as close to a reference design as you'd find. Didn't know there was an FPGA recreation, was it any good?

That VGA adapter looks nice, but not suitable for my Coco I don't think, seems to want a Coco3. Wonder if it's still made?

[alexh]

Didn't know there was an FPGA recreation, was it any good?

I never had an original CoCo but yes everyone liked it at the time but only a few weeks later MiniMig came out and everyone forgot what a triumph it was.

http://www.davebiz.com/wiki/CoCo3FPGA#O ... nd_history

That VGA adapter looks nice, but not suitable for my Coco I don't think, seems to want a Coco3. Wonder if it's still made?

It worked with CoCo2 (with a mod), CoCo3 (plus lots of other 8/16 bit home computers of the era). It is still the lowest cost Scandoubler ever using the Averlogic AL250/AL251 ASIC. It was only 16-bit colour so not compatible with AGA etc. which requires 24-bit (without loss of quality)

[rubber_jonnie]

Didn't know there was an FPGA recreation, was it any good?

I never had an original CoCo but yes everyone liked it at the time but only a few weeks later MiniMig came out and everyone forgot what a triumph it was.

http://www.davebiz.com/wiki/CoCo3FPGA#O ... nd_history

That VGA adapter looks nice, but not suitable for my Coco I don't think, seems to want a Coco3. Wonder if it's still made?

It worked with CoCo2 (with a mod), CoCo3 (plus lots of other 8/16 bit home computers of the era). It is still the lowest cost Scandoubler ever using the Averlogic AL250/AL251 ASIC. It was only 16-bit colour so not compatible with AGA etc. which were 24-bit (without loss of quality)

Shame it was undermined by the MiniMig, looks like a good project. I expect it could be made to do Dragon hardware too without many changes.

It's always nice to have a choice with things like Scandoublers, shame it work with AGA, but I expect it got a lot of love at the time. My Coco is a 1, so only has RF out, well until I did a composite mod :)

[rubber_jonnie]

Will revisit the Coco today and try to get the sound sorted.

Oddly the composite out has gone very crappy, so might have to revisit that. Annoying.

[rubber_jonnie]

OK, so the wonky composite was an easy fix. The wire I'd used for 5v was not great and the solder hadn't taken well. I replaced that and the video out was back to nice and sharp again.

The sound is another story however.

At first I suspected it was just a question of me wiring it wrong, but a look at the schematics and I can see I'm correctly connected. Hmm.

So next I traced back from the audio out (pin 3 of the modulator) all the way back to pin 11 of the 6821. The circuit is all good then.

Still no audio out when I run a 'sound command' though, and nothing at all on pin 11 of the 6821. Dead 6821 perhaps I thought, but no, I dropped in a spare and still nothing.

Next up I need to work my way through the service manual, see if I can find any clues.

Otherwise, sound aside, it seems to be running just fine.