Hum and noise, or the game only runs with the vocalizer unplugged from the sound board (page 79).

Xenon vocalizer: hot diodes, hum, or game will not run with it attached

Cause: Three 1N4004 diodes CR1-CR3 in series in the lower corner drop the voltage to the regulator and run hot until they fail; dried capacitors or a bad voice ROM are other causes.

Checks

• Look for discoloured diodes and board around CR1-CR3.

Fix

• Replace CR1-CR3, mounted on a small heat sink, and the regulator next to them; check capacitors and the voice ROM.

Systems

• Bally MPU AS-2518-35

Games

• Xenon

Related tips

• Testing a coil diode
• Testing the diode on a coil
• Which way a coil diode goes
• Which way a coil diode goes
• Testing a lamp diode
• Getaway: beacon runs nonstop in test and driver board C11 overheats
• What the coil diode does and how a bad one shows up
• Replacing a sound board with a chime box

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)