Sound works for 5 to 20 minutes and then stops. Pressing the sound test button still gives speech, but no other sounds. Supply voltages are close to normal.

Sound works for a few minutes then quits, speech still works: cracked IC solder joint

Cause: A bad solder joint on one of the chips on the sound board, which opened up as the board warmed.

Checks

• Measure the sound board supply test points first (about +15, -15 and +5 V).
• Reflow the sound board connector pins, which often crack on this generation.
• When the fault appears, use a logic probe on the sound board chips to find a pin with no activity, then inspect that chip's joints.

Fix

• Reflow the cracked joint on the chip (and any cracked header pins).

Systems

• Williams System 7

Games

• Jungle Lord

Related tips

• Setting up a sound board for speech
• Sound board jumpers for sound-and-speech games (2K ROM)
• Sound board test button gives no sound: normal on Joust
• Missing words or sounds from cracked connector pins
• No sound effects in play though speech works: check the sound board PIA
• No sound in play or solenoid test, and grounding inputs does nothing
• Sound board supply facts
• System 6/7 sound and speech board ROMs

Source: Pinball Repair help group!! (Facebook group)