I’m new on repairing Bally/Stern SS boards, and now I’m trying to resurrect a Stern Lectronamo.
The cpu is a MPU100, I’ve read some guide on the web but I still have the solid LED on.
I rebuilt all the reset section because some acid damage was visible, but this was not the problem, I mean… I’ve stable +5V on pin 40 of CPU U9, so reset seems to be ok.
New sockets for U6/U7/U8 and with multimeter the continuity from pad to pad is ensured, also where old sockets are already installed (U9/U10/U11).
From the guide and following pinwiki, at least the first flicker is needed and, in order to have it, the only necessary components are U9, U11 and U6. Perfect… I still have the solid LED on, +5V on pin 40 and grounding pin 40 to 39 nothing happens. Ok, the voltage drops to +0V but the led doesn’t flick. At the moment, the only measure not quite right is about pin 5 of cpu… VMA signal must pulsing, but in my case is high +5V.
I read that three are the ICs involved… U14/U15/U16 but in most cases U15 is the culprit. So I took form another board the U15, replaced in my MPU100 and.. tadaaaaa... nothing. Always solid LED on.
Now… it’s becoming a personal case. I don’t never give up! Never. And I want to find the issue without changing all components…
Anyone has suggestions for me?
Any help would be appreciated.