Picked up a Jungle Lord that had been in a flood (but not up to playfield), gotten most things working, but the sound is very quiet. All sound works, speech works, fader on sound board works. First thing I suspected was that the pot in the bottom had been damaged by the water. Twisted it back and forth, and it controls the sound fine, no drop outs like I usually see in bad pots. Im not quite sure how to measure a potentiometer, but I cranked it to max and checked the resistance, got around 40 ohms from left to middle, 1.5k from middle to right and from left to right. Did the same on my Black knight, got the same readings, so it seems like the pot is fine. Measured the speaker, 4 ohms. Seemed weird since the schematic says 8 ohms, but again my Black Knight measures 4 ohms... Not sure what the volume potentiometer is supposed to be since it's not listed in the schematics that I can find, so I also can't try just splicing a mid-valued resistor in to rule it out.

Recapped it, no change. Swapped my Black knight board in, still didn't work. So it's something with the rest of the game. Basically the pot, the speaker, and the power supply? Voltages all seem fine. (12V, - 14V, and 4.98V). Tested the resistance of the pot and speaker directly from the connectors, matches black knight.

Finally found it. Speaker actually was bad, despite reading fine. Stuck a car speaker i found lying around to test, worked fine.