The Naked Atari 800

[PhilC]

@rubber_jonnie what's the part no. For the CTIA? I've probably got one, no GTIA spare though. They are getting very rare now.

The PAL CTIA part number is CO14889-03, though I do have a buggy GTIA which should be good enough. I'm more interested in an Antic (CO21698) as that is the one thing I'm missing.

Not sure if you might have one of those at all?

Cheers

Yes, I think I do have one, will let you know

[rubber_jonnie]

The PAL CTIA part number is CO14889-03, though I do have a buggy GTIA which should be good enough. I'm more interested in an Antic (CO21698) as that is the one thing I'm missing.

Not sure if you might have one of those at all?

Cheers

Yes, I think I do have one, will let you know

Cool thanks 😁

[stephen_usher]

Are you loading the +5V rail? If not then current will pass through R203 and bring the +5V side up to the same voltage as the input.

[rubber_jonnie]

Are you loading the +5V rail? If not then current will pass through R203 and bring the +5V side up to the same voltage as the input.

I tried by connecting the mainboard with no ICs installed, but perhaps it wasn't enough?

I really didn't want to risk damaging anything important, but I will try again later or tomorrow with something more substantial in the load department and see what's what.

Seems a risky proposition to potentially allow 12v into the 5v line.

[stephen_usher]

more substantial in the load department and see what's what. Seems a risky proposition to potentially allow 12v into the 5v line.

With the 33 ohm resistor is would be low current, and the expected resistance of the rest of the machine would probably make it just a voltage divider anyway. (That would mean the rest of the system should be 23 ohms.)

[rubber_jonnie]

more substantial in the load department and see what's what. Seems a risky proposition to potentially allow 12v into the 5v line.

With the 33 ohm resistor is would be low current, and the expected resistance of the rest of the machine would probably make it just a voltage divider anyway. (That would mean the rest of the system should be 23 ohms.)

Cool thanks. Bloody power supplies are the devils work!

[rubber_jonnie]

@stephen_usher

Thanks for your expertise, as usual you hit the nail on the head.

I added additional load and there is 5v at the PSU output. Thank heavens for that!

What is really handy about the 400 and 800 is that there is an interlock switch which powers the machine down when the lid is open, and that allows me to kill power right away if things look bad. And it all looks great 😁

I've now also checked with all the chips I have and the CPU, ROM and RAM boards fitted and get 4.9v.

I also get 5v,-5v and 12v at the 4116 RAM ICs.

[ijor]

The PAL CTIA part number is CO14889-03,

Just for the record, that is PAL Gtia, not Ctia. There is no such thing as PAL CTIA. But even NTSC CTIA is pretty rare. Note that you don't need CTIA, GTIA runs just fine in the 800.

[rubber_jonnie]

The PAL CTIA part number is CO14889-03,

Just for the record, that is PAL Gtia, not Ctia. There is no such thing as PAL CTIA. But even NTSC CTIA is pretty rare. Note that you don't need CTIA, GTIA runs just fine in the 800.

Yeah it's odd, that number came up as a PAL CTIA but it is indeed a GTIA. That's the internet for you!!!

I have one of the GTIA's that has a bug and I will use that. it's good enough for testing, I just need to find an Antic now.

[rubber_jonnie]

Well, I think in 2026 I need to get my IC storage better organised, I just found some CD4050's in my IC drawer...

So, A103 is now populated and I'm just waiting on the LM3086. Nearly there.