1942 repair log

Got for repair an original Capcom 1942.

It's a two PCB stack made of a CPU board

and a VIDEO board

When I applied power the board booted but I could not coin up

Looking at schematics the coin input from the edge connector is routed to pin 14 of a 74LS367 @A6 on CPU board

 

 

Checking it with a logic probe revealed a floated signal (usually inputs are in high state pulled-up by resistors)

Using a multimeter I measured few Ohms of resistance between pin 14 of the 74LS367 and GROUND (whereas usually it should in order of MegaOhms)

I pulled the IC :

 It passed the out-of-circuit testing on the Retro Chip Tester :

 But it failed the one of my ChipMax2 programmer :

I fitted a socket and a good IC :

 This fixed the issue, the game registered again coin input.No other problem was found therefore board 100% working again!