Rolling Thunder pcb sound issue

[Derezz]

I hope somebody can help?
I have two RT boards, and old version, and the new version. Now i had them in storage and due to mouse damage the new version has a couple of corroded chips and won't play, just a fuzzy gfx screen. Plus it had the correct in game soundtrack that the old version didn't.

So I've swapped the RT1 - 16 roms over and the smaller 1-5 from the new to old board in the hope it'll work, and it does! BUT I have no 'kssh' gun firing or enemy 'argh' sounds when they're shot. All the other sounds seem to be there.

Does anyone know where the sounds are located on the pcb? I've swapped both sub boards to and fro and still get the same.   
Bit stuck. Anyone have any ideas ??

[Derezz]

Quick update if anyone's interested...

After careful examination, the missing sounds were actually there, just REALLY quiet and the in-game music was drowning them out totally. So advice from a good friend of mine was to swap the capacitors on the sub-board. So my trusty soldering iron came out, old capacitors removed and new capacitors soldered on, six of them in total. It's back to normal again, all sounds, just great. 

Just Robocop to fix now 

[DarthNuno]

Thanks for the resolution details, it's important to know the solution, may be useful for other fix with similar symptoms 
I've just seen a RT board for sale by the way, right here (don't understand why the seller mentions '(irem)' by the way )

[Derezz]

Thanks, and yes it might help others in the future perhaps, plus was an easy fix 

IREM Rolling Thunder? Maybe he's got confused and means R-type perhaps? Who knows. Buyer beware though, there are two versions of Rolling Thunder. The old version has different in-game music and you can't select the level-skip at the beginning. New version is much better. Make sure they specify which one's for sale