3o. When things don't work: Sound Problems.
The sound on WPC games is very robust; it just doesn't fail too often. But here are some things that do fail related to sound:
Re-seat all the sound board ribbon cables. Surprisingly, this fixes a large number of WPC sound problems!
Bad rectifier diodes on the sound board. Often these become leaky and can cause intermittent problems before they total short.
Speakers blown: yes this happens more often than you might think. If the game was in a noisey arcade, the volume could be up so loud it blows the speakers. You can test the speakers (with the game off) using a 9 volt battery. Momentarily hook the battery up to the leads of the speaker. You will hear the speaker cone pull in if the speaker is good, when you attach the battery to the speaker. Make sure you check the speaker in the bottom of the cabinet too. Often if one speaker is blown, the others will not work.
Main amplifier is bad: the sound board uses a LM1875 as the main amplifier. This device has a large heat sink attached to it. Often, this component has heat failure. The sound works fine until the game warms up for five minutes or so. Then the sound starts cutting in and out. You can use a logic probe on the leads of the LM1875. If the probe's beeps correspond to the cut in sound on one of the leads, the LM1875 is probably bad.
If the LM1875 isn't at fault, check both of the op-amps too. Depending on the revision of the sound board (DCS or pre-DCS), these audio amps can effect a certain type of sound they amplify.
On DCS games, the DAC for the DSP chip dies, and the TDA2030 amps are pretty fragile too.
Volume up FULL and Can't turn it Down.
The volume control on all WPC games is electronic. On pre-WPC95 games, this is controlled by an electronic prom pot. This E-pot is a X9503, at location U5 on the sound board. If turning the volume up or down has no effect, and the volume is stuck on full blast, this is the first component that should be checked. Also the capacitor C18 (47 mfd, 25 volts) that connects to the E-pot can fail too, and should be checked.
Lots of Static.
Problem sound boards can produce a large amount of static. The TL084 quad Op-Amp (U21 on WPC-S and prior) can be the cause of this. Also the TDA2030 amp can also cause this. Finally the large filtering 1000 mfd 35 volt capacitors can also be the problem. Finally check for cracked solder joints on these 1000 mfd caps (solder jumper wires, as done to the bridge rectifiers explained earlier).