Got this Frogger PCB from my friend Josef for a repair.Actually it was the Sega/Gremlin version which uses Konami Classic pinout (like Gyruss, Scramble and many others):
PCB played fine but had a strange issue where sound was very quiet on my supergun while was completely silent on a cabinet.All audio circuitry is located on upper board.Looking at i I could notice that someone had previously reworked (replacing it perhaps) the M51516L amplifier ending with break some traces and using some jumper wires to fix it:
Luckily schematics were available so I went to check every connection in this part of circuit.Everything seemed fine until I came across to something odd : PIN 6 (ground) of M51516L amplifier was intentionally jumpered to positive terminal of a 100uF 25V electrolytic capacitor (so both terminals was shorted to ground) :
while schematics showed it connected to collector of a transistor through a 1KOhm resistor :
Removing this jumper wire restored full sound.