Bubble Bobble repair log #5

Received for repair from New Zealand an original Bubble Bobble PCB.Set is made of a CPU board

And a VIDEO board:

It came already adapted to JAMMA so it was just matter to plug it in.I did it but nothing came up on screen. I noticed wires were soldered onto the pins of ‘H’ connector and then a molex connector was used to carry power to JAMMA fingerboard:

I didn’t like this solution because it can cause loose connection so I removed the molex connector and soldered wires directly to JAMMA fingerboard.In this way the board properly booted up, games was perfectly playable with sound too but every alternate horizontal line of graphics was missing :

From top of my experience I know this kind of issue are most of times caused by bad counters (74LS161/163/169).Looking at board I spotted two rows of 74LS169 on bottom VIDEO board:

From schematics I could see they are involved in VIDEO RAM data bus, this made sense :

I went to probe these 74LS169 in circuit with my HP10529A logic comparator, all of them passed the test except the one @IC64 that gave troubles on all its outputs:

I pulled the part out :

It failed the out-of-circuit test on my BK560 :

I installed socket and a fresh IC :

This cured the issue and fixed board completely.End of job.