coin in problem on GK and other

[Badbaud]

I am getting a SMD rework system in to the shop and want to repair that nagging coin in error that is caused by a single IC on various boards.The attached picture is of a GK board which I call the NEW style, not seen is the older GK board with the single row black connectors for the piggy back board and finally, not shown is the S2000 board.
On each of these versions what is the IC location number and part number that needs to be replaced?

[Tilt]

The photo is a 3902 MPU board used in Game Kings and I-games.  There were earlier versions, 3502 and 3802 models that were all EPROM based.  They did not have SIMM sockets.  I don't know about the earlier versions, but if you have a persistent Coin-In Jam accompanied with a Meter's disconnected error it is usually U74 that has died.  Sometimes you can see signs of physical damage such as bubbles orburn marks on the top of the IC.  It is next to the MML connector, so I made a heat shield out of a piece of aluminum flashing to keep from melting the plastic connector.  Learned that lesson the hard way.  It didn't prevent you from using a MML2 sound board, but didn't look very good.

The S2000 50X MPU board has the same component, but I can't remember the chip number and don't have access to my schematics right now.  I want to say it's U67, but that may not be correct.

[Badbaud]

That is a good start, maybe someone else will chime in on the earlier GK series without SIMMs