A4000 repair

[obitus1990]

I powered on my A4000 yesterday (it had been recapped and repaired of (minimal) battery damage probably 6 years ago) and was greeted by a screen with slowly changing colors on it (mostly shades of green and blue, some purple). I have CS-MK2 CPU card in it, which I removed and tested in another 4000, and it works fine, so I put it back into the non-working computer. Then I removed all the SIMMs, and it behaves the same with the changing colors. No other cards are in the machine. The power LED doesn't change brightness. Any suggestions on where to start looking? I have a scope, dmm and logic probe at my disposal to check signals, but, don't know where to start. I've built a 4000 up from a bare repro board (my other 4000 mentioned above), so soldering/trace repair won't be an issue.

Thanks!

[klx300r]

First thing I'd do is to check the PSU

[TjLaZer]

Check the CPU slot. Use some DeOxit cleaner on it and make sure it's got a good connection.

[obitus1990]

Regardless of which CPU card I use (I have a 3640 and the CS MK2, as well as a BG9060 I built), once I swap out the ROMs for DiagRom, it fails to detect any RAM. ChipRam fails, so I tried another appropriate SIMM, same issue, removed and swapped the fast ram, no change. What's the most likely culprit for this behavior. I really can't interpret what the output of diagrom, as it's above my knowledge level (serial port output is the only part that works for me). If I have SIMMS on the CS-MK2, it will get further in the test, but, fails with a 'PANIC, inadequate resources to go further" statement.

[Kin Hell]

If your Buster Chip is in a socket, make sure it's fully seated. It's best to push down on the socket with the Motherboard out of the Chassis & on a firm Anti-Static surface. Pressing down on any Socketed chips with the Chassis standoff's in place will allow the board to flex & excessive pressure could break the Motherboard.

Make sure the CPU edge connector is fully seated too. Changing CPU cards in the A4KD can fail if you don't support the edge of the motherboard. The tapered end/edge of a pencil eraser is a better substitute for finger tips unless you're thick skinned.
Again, this is best fitted to the Motherboard out on the workbench & then fit to the Chassis stand-offs.

That said, a lot of what appear to be, successful Battery repairs.... can lead to the issues your seeing now many years down the road. I dare say some of the memory tracks are burnt away in the layers of the Motherboard substrate when the battery leaked all those moons ago.

[Tchucolate]

Are these colours flakey, flickery, or are they solid colours, which change over time? Also, are these colours consistent? They sound like diag colours, and their type could be useful. Maybe write them down, and then check online for A4000 diag colours.

I believe green is mem related, red also. But you need to check.

I have an A4000 fixed from totally dead, and in my case the Fast RAM slots had some damage, and one of the Octal transceivers, needed for RAM to work, was dead, as it was inline with the battery. In fact, have a watch of this, series, it might help you...

https://www.youtube.com/playlist?lis...MpcwY2bLWhRQAV

It could be a failure in your memory, I believe if you see valid diag colours, then this indicates your CPU is working. And if you put the original Roms back in, and the diag colours are showing up as green/red, this shows the CPU is working, and using the ROMs to show the various diag colours.

Anyway, put your normal ROMS in and CPU and see if you get consistent diag colors and then list these for us here.

[obitus1990]

It's not an issue of a loose chip or connector as I had removed the board from the case to work on it at the bench, and reseated them all there. The voltages are all measured within spec. The normal ROMS also display a series of colors on the screen, in no particular order. DiagRom, as it goes through addresslines during memory check, will change the screen colors red, blue, green, yellow, etc. I will play around with this a bit more, as I believe all the "main parts" (customs, CPU card) and RAM are good. Failing that, I'll do a transfer over to a ReAmiga board. Last time I did one was 2018 after building up one of those Alice+ boards I bought from Hese on Amibay....not looking forward to doing that again

[8bitbubsy]

I'd try to look for any corrosion, and work from there. The caps leak as well on these mobos, and if you didn't properly neutralize the leakage during the recap (and battery fix), the corrosion can grow/live over time and do more and more damage. You often can't even see the leak with the naked eye unless you know exactly what to look for.