Another Amiga 2000 motherboard repair thread

[HanJammer]

Some time ago I bought this broken A2000 (I knew it was broken from the auction description - no picture - black screen on both composite and VGA output). I already repaired another A2000 some time ago (which had similar symptoms) so I figured out it may be easy fix. Battery obviously leaked but two traces under it were OK (checked for continuity). I cleaned the motherboard with citric acid (much better than white vinegar). CPU socket was severly coroded - pins literally broke off when I removed the 68k, so I replaced it. Unfortunatelly still no success (no picture). I swapped the socketed chips and CPU from my other A2000 (one by one or in pairs first Paula + Denise, then Agnus, then Gary, then CIAs, then Buster and still no success. I also swapped EPROM. CPU gets very nice stable 5,2V (PSU from my other A2000). It also gets correct clock on the CLK pin. I hooked up Salae to some address pins on both CPU and EPROM but I don't see any activity after powering off - just some drops when I turn off the power. Motherboard is less simple than some XT motherboards I fixed in the past, but don't really have much experience in diagnosing Amigas, so any help would be appreciated (what to check, any typical things break here?).

Some pics: https://imgur.com/a/MphBK0F

 

[Pior]

Check all the trace lines to and from the CPU socket. If the battery did leak and may of eat threw one of the tracers and that is all it takes.. Check the continuity from the socket to the next connection.,. Dark spots in the tracers are corroded and can be broken..

 

[HanJammer]

I'm PC guy living in the 286/386/early-486 era so I'm well off these problems and none of them exist on this board (like - I checked all the traces with darker spots - in fact there is only one like this - visible on the photo).

 

[riri]

I had a similar problem, the solution was to replace the cpu socket.
Cleaning the area before placing a new one.

 

[HanJammer]

I had a similar problem, the solution was to replace the cpu socket.
Cleaning the area before placing a new one.

"CPU socket was severly coroded - pins literally broke off when I removed the 68k, so I replaced it."

So it didn't helped. Also it wasn't bad under the socket - no corrosion at all...

 

[sagias]

had same problemm and it was eprom,take a multimeter and see first if resets, on pin 18 if not test ls 08 and 32
or better burn a diagrom first.

 

[HanJammer]

had same problemm and it was eprom,take a multimeter and see first if resets, on pin 18 if not test ls 08 and 32
or better burn a diagrom first.

I hooked up the logic analyzer to the CPU pin 18 - after powering on it's a low for a short while and then is high.

I also tested all socketed the chips (but Buster) in second working motherboard and they worked fine. (I tested working Buster in the non-working motherboard earlier and it didn't changed a thing).

Also there is no activity on CPU address lines after powering on so I guess burning diagrom won't change a thing at the moment.

I will check all the address lines and data lines between EPROM and CPU socket.

What else to check?

 

[HanJammer]

D4 and D6 line had no continuity between CPU and EPROM (I don't see any apparent damage on these lines but multimeter doesn't lie). Blue wiring them solved the problem.

https://i.imgur.com/upe2XVq.jpg

https://i.imgur.com/9qcS0ka.jpg

Everything else on this motherboard does seem to work perfectly fine.