A very unusual S+ problem for me.

[stayouttadabunker]

This is the first time this has happened to me.
The machine is an S+ Double Bucks 2CM with SS7939 and SP1019 chips installed.
The SP1019 required a 16MHz board to run it, according to the PSR.
Been running fine for at least 7 years with no problems larger than jammed quarters
in the bottom of the hopper bowl or a coin mech jam.
Normal maintenance kept it working well forever.
A real workhorse!

However, this morning, a customer was playing it and it stopped accepting coins.
All coins fell back into the coin tray below the door.

No error codes showing on the display at all and the candle wasn't even flashing?
The display & candle works fine.

First thing I did was see if the coin-in optics would register a "Service Credit" to the MPU....no go.
I swapped everything out one by one until I pinpointed the problem.
Goes back to the MPU.
Moved existing SS, SP, and CMOS to a new 16MHz board and problem went away.
Machine back in service.

I have no noticeable burned traces anywhere on swapped board.
Even tried it in a different known good test machine...still won't accept coins.
Battery is strong....registering 3.47Vdc on my dial.
What went south?
What IC component gave out?

Here's a couple of photos of the MPU in question.

Click on photo to enlarge if needed...>>>