Got this board on the bench, making progress. Sometimes when I power it up it will flash the diagnostics LED but usually not (Why?)
-The magic smoke came out in the general area of U38. Display showed a very bright 0 in the 11th or 12th position on the top row.
-Pulled the ROMs and verified good.
-Replaced & socketed PIA U38 & U51
-Leon's test rom will run, verified 2-17 are toggling on those 2 PIAs
When the diagnostic test runs, I get 3 long flashes followed by a very short pulse before repeating. Is this code 3 (U51) or 4 (U38)?
Next planned step is to pull the SN74154 in U44 and see if that affects the diagnostics test. If not, pull and test U30, U39, and U40. Would like some clarity before I start pulling parts. Any other ideas?