I got this faulty Pyros (US version of Wardner) PCB from Ebay :
It was not really cheap but it was worth the buy since, on the basis of the seller description, I was confident it could be an easy fix.Board showed an ‘I/O ERROR’ upon boot:
I knew from my experience that this board produces the mentioned error when, indeed, there is some troubles with the inputs during the startup sequence (also a simple buttom pressure would cause it).So for first I went to check with my logic probe all the inputs probing pins on the JAMMA edge connector.All of them were high except the ‘COIN 2’ (pin 16 solder side) which was stuck low.I could trace it back to pin 17 of a 74SL240 @20N :
I could measure only few Ohms of resistance between this pin and ground, this meant internal junction was nearly shorted to GND:
Once desoldered the chip, it obviously failed the test:
With a good chip, the board entered in game with no further issue.