Mar 292020
 

Got two Pacland pcbs to be repaired from a friend.

Fist one is a Sidam Pacland which showed the following problem:

 

All the screen had shadowed colours going up and down vertically.

By expecience whith similar problems on different hardware I understood it was a Hblank problem.

The game didn’t shut off the screen at the borders so the monitor didn’t have anymore the black reference.

Looking at the schematics I found immediately a clear reference to the blanking circuit:

 

Compblank was oscillating, while COMPBLANK A and \COMPBLANK A were stuck.

Chaning the 74LS74@6M fixed completely the issue