exxos's Atari, Amiga & retro forum

rubber_jonnie wrote: 19 Dec 2025 14:10 Yeah, going straight into diags isn't a good sign, but at least it's pointing at the RAM. Standard IC's so should be an easy fix. It's worth checking the keyboard and sound whilst diags are up.

I think there are keyboard issues as I can't abort the test anyway.

stephen_usher wrote: 19 Dec 2025 14:26

rubber_jonnie wrote: 19 Dec 2025 14:10 Yeah, going straight into diags isn't a good sign, but at least it's pointing at the RAM. Standard IC's so should be an easy fix. It's worth checking the keyboard and sound whilst diags are up.

I think there are keyboard issues as I can't abort the test anyway.

So does the reset button send you straight back to diags? Best to deal with the RAM first I think.

rubber_jonnie wrote: 19 Dec 2025 14:29 So does the reset button send you straight back to diags? Best to deal with the RAM first I think.

Yes it does... However, I'd rather see what other possible issues there are first. Looks like there's no keyboard scanning going on, well, not proper ones anyway. It could all well be to do with bad sockets as they're single wipe things.

Well, U25 (4051, keyboard scanning output) has signals going in and nothing coming out.

stephen_usher wrote: 19 Dec 2025 14:44

rubber_jonnie wrote: 19 Dec 2025 14:29 So does the reset button send you straight back to diags? Best to deal with the RAM first I think.

Yes it does... However, I'd rather see what other possible issues there are first. Looks like there's no keyboard scanning going on, well, not proper ones anyway. It could all well be to do with bad sockets as they're single wipe things.

Sockets vary between machines. My 600XL was almost fully socketed when I got it, but none of my 800XLs had any sockets at all. I have seen drops straight into diags with no keyboard activity before though, it went directly into a RAM test and then none of the function keys worked at all.

Could also be a bad keyboard connector, they aren't the best and the ribbon can be fragile.

Not a surprise, but no CD4051 chips in stock.

RAM problem diagnosed.... Piggy-backed a 4164 on U13 and I get the Ready prompt! Totally luck that it was the first chip tested.

I can also use the keyboard. Obviously when that RAM self-test fails it doesn't initialise the keyboard scan.

stephen_usher wrote: 19 Dec 2025 15:36 RAM problem diagnosed.... Piggy-backed a 4164 on U13 and I get the Ready prompt! Totally luck that it was the first chip tested.

I can also use the keyboard. Obviously when that RAM self-test fails it doesn't initialise the keyboard scan.

Nice one!!

As I said, I have seen RAM problems where the keyboard will stop working, so I'm not 100% surprised there.

Time to desolder that RAM and fit a new socket and a new one.

Fixed the RAM, verified the machine and then put things back together, testing at each step.

Powered on and went into the diagnostics to test the keyboard.... Two keys needed some Electrolube to get them working again. Once this was done I hit reset and...


Power cycling and I get the same each time, often without the correct vertical sync!

I'm guessing a bad connection on the GTIA socket. I'll see if I can open it up again after I get back from the model railway club.