I have a couple of faulty A500+ Rev 8A boards both with battery damage. One is a total mess the other had 2 /3 broken traces which I have fixed, but I need some advice as what to try next.
What I have done so far:
- On both boards, I have tested and fixed any continuity issues, focussing on the usual area around Gary,
- Replaced Gary's socket.
- replaced the 74LS244 in U12
- Swap tested all of the ICs with known good chips / board.
- Tested clocks / power.
So this is the current state of play with each board.
Board 1 (the lightly damaged board):
I get black screen and the power light stays dim.
There is a sync signal to the monitor albeit no pic.
I have tested with a diagrom. No difference still black screen.
I have scoped around and there does not seem to be any activity on the address lines.
Reset lines on CPU / Gary seem to behave normally low for a moment and then stays high.
I am not sure what to try next on board 1?
Additionally, Agnus is welded in to its socket on this board. Later I plan to replace the socket with a better one but can not get it out. For now I plan to leave it alone unless it is likely / potentially part of the fault?
Board 2 (the horrendous board that now has so many botch wires it looks like a breadboard project :
This board amazingly is getting to a green screen which I know indicates a ram problem.
I tried piggy backing the ram but this did not change anything.
My question here is simply I am not sure if I should start desoldering the ram OR is it more likely to be the other 74 logic chips near the damage?