Acorn Atom Replica build

[PhilC]

Are you going to get a 3d printed case for it?

[rubber_jonnie]

Are you going to get a 3d printed case for it?

Undecided as yet.

[stephen_usher]

Go old-school and make a nice marine plywood case. Very popular in the very early 80s for kit computers, such as the Nascom 1. :-)

[rubber_jonnie]

Go old-school and make a nice marine plywood case. Very popular in the very early 80s for kit computers, such as the Nascom 1. :-)

Well I could do two, one for my OSI600 as well :)

[rubber_jonnie]

OK then, I think the Atom may have some bad RAM:

20260310-114546.jpg

It's been running all morning just doing a light task of printing something then going back and doing it again...

The 2 ICs at the bottom are minimum for the system to run and are OK, but the two dark spots don't look good to me. I have some spare 2114s so will just swap them out, but I also have a decent RAM tester coming which will test 2114's so once that gets here I'll pull the lot and test fully.

There is another similar RAM bank, but everything is glowing nicely there so I'm assuming it's good until such time as I've got the tester.

[PhilC]

You could write a little ram test program if you know the ram address?

[rubber_jonnie]

You could write a little ram test program if you know the ram address?

I do have a RAM tester routine somewhere but I'll have to get to it later. Also, I have one of these coming:

Screenshot 2026-03-12 at 11.16.40.png

So I'm not in a huge rush. I have already replaced it and it seems to be fine, all glowy and hot :)

[rubber_jonnie]

@PhilC

Do you by any chance know what crystals are in your Atom?

As per the BoM and schematics I have a 3.58Mhz and a 4Mhz crystal in mine but I'm getting NTSC output for some strange reason.

Atari use 3.58Mhz in their NTSC machines so I have also tried a 3.55Mhz crystal as well but it still shows as NTSC for both on composite out.

I get 1Mhz as the CPU clock so that means the 4MHz crystal used for that is being correctly divided by 4.

[PhilC]

@PhilC

Do you by any chance know what crystals are in your Atom?

As per the BoM and schematics I have a 3.58Mhz and a 4Mhz crystal in mine but I'm getting NTSC output for some strange reason.

Atari use 3.58Mhz in their NTSC machines so I have also tried a 3.55Mhz crystal as well but it still shows as NTSC for both on composite out.

I get 1Mhz as the CPU clock so that means the 4MHz crystal used for that is being correctly divided by 4.

I've just checked my Atom audits the same as yours. Not measured the composite out signal on mine as I've now got the RGB2HDMI.

[rubber_jonnie]

@PhilC

Do you by any chance know what crystals are in your Atom?

As per the BoM and schematics I have a 3.58Mhz and a 4Mhz crystal in mine but I'm getting NTSC output for some strange reason.

Atari use 3.58Mhz in their NTSC machines so I have also tried a 3.55Mhz crystal as well but it still shows as NTSC for both on composite out.

I get 1Mhz as the CPU clock so that means the 4MHz crystal used for that is being correctly divided by 4.

I've just checked my Atom audits the same as yours. Not measured the composite out signal on mine as I've now got the RGB2HDMI.

Hmm interesting.