Got for repair from USA this faulty original Ghosts’n Goblins PCB, a two stack made of a CPU board :
And a VIDEO board:
Both boards were very dirty especially on solder side:
Some areas were corroded too:
Before applying power I washed both boards and neutralized the corrosion with some vinegar.On smoke test the game booted up, it was playable with sound too but with noticeable graphical issues :
I polished the contacts inside the connectors of the ribbon cables and the big vertical bars disappeared but backgrounds were kinda pixelated :
The circuit which generates the tiles lies on VIDEO board and it’s labeled as “SCROLL” in schematics (last three pages of PDF).Checking it with a logic probe I quickly found a 74LS273 @6A with a dead output:
The scope confirmed the output (pin 15) was floating while input (pin 14) was toggling:
The signal from this dead output is called ‘SVFLIP’ in snippets of above schematics and it’s routed to the inputs of a 74LS86 @5B which outputs some address lines for the backgounds ROMs:
Probing the 74LS86 @5B with my HP10529A logic comparator revealed troubles on output pin 3 and 6:
I removed it along with the 74LS273 @6A :
Both chips failed the out-of-circuit testing :
I installed sockets with good chips :
Backgounds were so restored and board 100% fixed.End of job.
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