Weird Sound Problem 2600 JR

[Qixter]

Picked up a 2600 jr knowing it was untested. Cleaned it up and got it working. One issue is a weird sound problem. For example, Asteroids plays fine but does not have the background sound or the sound when you hit an asteroid. The ship blaster, thrust and the alien ship sounds are all perfect. See attached for example. Tried Space Invaders and couple of other games and same issue. Some sounds but not all. I cleaned the board to include the pin contacts, replaced the clear silver polystyrene audio caps, checked for cold solders, tried adjusting the RF Modulator (L6) l also checked for dark spots and broke traces. I cannot find a schematic for this particular board so I am stuck on what to trouble shoot next. Appreciate any insight or direction.