exxos's Atari, Amiga & retro forum

Ahh, that's better 😁


Just need to test audio now.

It is easier to read, indeed.

stephen_usher wrote: 18 Feb 2024 17:49 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.

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.

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

alexh wrote: 19 Feb 2024 13:40 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?

rubber_jonnie wrote: 19 Feb 2024 14:26 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

rubber_jonnie wrote: 19 Feb 2024 14:26 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)

alexh wrote: 19 Feb 2024 15:09

rubber_jonnie wrote: 19 Feb 2024 14:26 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

rubber_jonnie wrote: 19 Feb 2024 14:26 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 :)

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.

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.