Bomb jack sound issues.

[penrhos]

I picked up a cocktail off ebay and lying in the bottom was a bomb jack PCB- it was filthy but remarkably corrosion & repair free.

I've made a jamma adapter and surprise the pcb works.

However the audio is distorted and there's a really loud buzzing, the amp gets hot too. I've double checked the adapter I made and it meters ok and matches the diagram I found on klov.

It looks like it's a bootleg rather than an original but as all the other stuff is working - video, coins, starts, sticks & jump. I think the adapter is right.

Sound is speaker + & - which I've connected to the speaker pins on the jamma edge connector.

Anyone had a simular issue?

 

[Asayuki]

Disconnect the jamma connector and measure for resistance between the outputs of the power amp and ground. Any reading other than infinite is a problem. Also, you might want to recap around the power amp and check short circuits on both sides of the PCB.

 

[penrhos]

Progress - amp is a m51516l and there's supposed to be a cap across the output pins.

Pulled this out and it was knackered.

100uf @ 25v replaced that and two others near the amp.

47uf @ 16v and 10uf @ 16v and the hum has gone. Still have a problem where it's really loud.

So next stop is checking the value of vr1 and the resistor in series with it - should be a 1K linear.