Received this Wild West C.O.W. Boys of Moo Mesa PCB for replacing electrolytic capacitors on the infamous ‘054986A’ audio module although sound was still perfectly working :

As usually I opted for tantalum capacitors, this was the final result:

But when testing the PCB I noticed coin input of player 1 was not working, this was confirmed by I/O check which showed this input as stuck:

As workaround somebody put the game into free play:

This is a common issue on the all Konami boards that share the same hardware design.The input signals from JAMMA edge are first routed to some some custom resistor arrays marked ‘005373A’ then to four 74LS257 which multiplex them :

Checking the involved part revealed that input of the 74LS257 @Q3 was almost shorted to ground as well as obviously the output of the resistor array @S15 connected to it:

So the problem was in either of them.Using an audible milliohm meter I was able to locate the point of less resistance with ground in the 74LS257:

So confident I removed the IC:

It failed when tested out-of-circuit:

Replacing it cleared the issue, input was no more stuck.End of job.

Had this bootleg of R-Type (manufactured by Philko) laying around since some time:

On power up board was stuck on this garbage static screen:

Like in the original Irem hardware main CPU is a NEC uPD70116 (a.k.a. V30)

Probing it revealed that the RESET signal (active HIGH on this CPU) was missing, pin 21 was going  LOW on boot with no transition from HIGH state hence no initialization of the CPU itself

But if I manually resetted the CPU by briefly shorting pin 21 to +5V via a 100 Ohm resistor, the board successfully booted and played perfectly:

Traced pin 21 of the CPU back to pin 10 of the uPD71011 whose pin 11 receives the RESET signal and invert it  :

Also the /RESIN input had no initial transition so the problem was upstream.Compared to original hardware the bootlegers semplified the power-ON delay circuit purposely omitting the M51202 voltage comparator (although  there is silkscreening and room for it).They used insted few discrete components like a diode, a resistor and an electrolityc capacitor which actually was not present @C6 (most likely it went detached)

This was the cause of the missing RESET.I fitted a 100uF 16V electrolytic capacitor (after experimented different values) and board booted all the time.Job done.

Received this original Ninja Emaki PCB (manufactured by Nichibutsu) for repair:

Board gave a solid black screen.After a quick visual inspection, I noticed one IC was missing from its socket @1B on CPU board:

My searches confirmed the missing IC was actually a PAL but sadly I had no access to other same PCB in order to read or reverse the device.Here bootlegs come handy since often they are perfect reproduction of the original hardware and, judging from pictures I found online, this was my case :

I quicky managed to find a Ninja Emaki bootleg and one received it I realized that the missing IC was a PAL16R4 so a secured registered PLD hence not readable or reproducible :

My only choice was  to take this chip from the bootleg and install it on the original board.I made it and board sprang to life:

Game was playable but background were scrambled as you can see from above picture.I noticed that if I pressed or flexed the board in some points, the graphics came back in place.A closer inspection revealed some dry joints on solderside of an EPROM:

Reflowing them fixed the board completely.