Moon Cresta sound issues

[Belike]

I received a Moon Cresta pcb on Galaxian hardware, I tested it with André's Galaxian to jamma adapter, the game runs fine, but absolutely no sound, setting the sound pot has no effect.
Maybe it is the sound amp (mb3712), but I have no idea how can I test if it is broken or not.
Where should I start?

[Belike]

bump

[Etienne MacGyver]

does the sound work if you directly attach a speaker to the pin on the board itself instead of the converter ?

in other words, is the audio pin correctly re-routed by the converter ?

it should be pin "v" on the componentside for +audio according to this :

http://www.mikesarcade.com/cgi-bin/spies.cgi?action=url&type=pinout&page=Pac.html

Take a speaker, connect one wire to the ground and while the game is running try the other wire on pin "v"