I started off trying to repair a dead board and discovered my working/reference board was also dead. It was working when I last packed it away!
Symptom was a black screen / no signal on SM124 and an empty white raster on a 1084 RGB CRT. No activity from hitting reset button.
Poked around quite a bit, checked voltage rails, re-seated the socketed ICs but no joy.
Could see video sync and RGB signals on the monitor socket (because: white screen, so..) but no interesting activity.
Scope on the ROM socket address/data pins - nothing. Just deadness after power on.
Checked the RESET signal to 68k... seems ok. Checked the BERR signal... same.
Checked HALT - it's low. So the HALT circuit is broken or more likely the CPU said HALT because of extra complicated stuff going wrong elsewhere. :/
Followed that around but nothing really interesting.
Randomly decided to swap the GLUE and retest. Now half the time HALT is low, the other half its high. o_O
Now put the old GLUE back in, now HALT is high. Great, random glitchy physical fault on the board.
Now I put it under the microscope and scan around for a bit. Nothing interesting for 99.9% of the board.... except one solder pad is green on the bottom side of the board. Hmm. It's a CPU pin.
Very crusty, green pin. All other pins look fine. No obvious reason.
- Screenshot 2025-06-11 at 15.32.06.png (821.27 KiB) Viewed 780 times
