TMNT pcb sound repair

This Teenage Mutant Ninja Turtles (TMNT) pcb was working but without sound, a common cause of no sound on a TMNT is a missing or bad 640khz resonator. The first one checked fine on the scope but the second one labeled X2 was dead. I replaced it and could see it working on the scope but this made no difference.

The Z80 and 6116 ram @ F16 both looked healthy and piggybacking the ram made no difference. I then decided to make use of the very nice high quality schematics available at jammarcade.net. The next most likely cause was the 74LS374 @ F21. This was confirmed bad with the chip tester and a new 374 brought all sound back except for the theme song.

The theme song is stored on a maskrom @ D5, I desoldered it at read it in my programmer as a 27C400 and it read as blank. I took another D5 maskrom off a scrap board and the theme tune returned.

Turtle power!