Weird issues with A4000

[Castellen]

Hard to say without a few measurements, but the clues suggest it might be an open circuit line in the register data or address bus.  Use a scope to check for normal looking activity on all lines of DRD and RGA at U400 and U450, usually not too hard to spot.

If there has previously been a lot of battery corrosion, this can damage the vias around the left hand side of the SIMM sockets, and some of those are part of the data/address bus that might explain your symptoms.  I doubt you'll visually be able to see anything useful, it'll need measurements to see exactly what's going on, after which it's easy enough to locate and repair an open circuit via for example.

Not sure if this is one of the boards I've worked on previously or not, but either way, feel free to contact me for repair options if you can't figure it out.

http://amiga.serveftp.net

[Castellen]

It was a guy in Denmark that did the previous work.
Where are you located?

I'm based in New Zealand.  The guy in Denmark (Jozsef) sends me his complex jobs for repair, though he's great with capacitor replacements, etc.


From your latest description, there's probably either a solder joint, PCB track or via that is cracked, causing the intermittent problem.  You might be lucky in that if you keep the main board in that position then it might be OK, or perhaps the fault will show up again.  These intermittent problems can often be unpredictable and difficult to track down.


Regarding the power supply, I'd recommend keeping the original one.  The design is fairly reliable, fit for purpose, and it's easy to replace the capacitors as needed.  Plus you don't need to mess about with modifying anything.