A coil or flash lamp is on solid at power-up (heat, smoke or smell), or blows its fuse straight away.

A coil or flasher energizes as soon as the game is turned on

Cause: Usually a shorted driver transistor (TIP102 or TIP36c). Less often a shorted pre-driver (2N5401/MPSD52/2N4403) or the 74LS374 latch that controls them. A badly soldered replacement TIP102 can also short again.

Checks

• Turn the game off at once.
• Find the coil's driver and pre-driver transistor numbers in the coil table at the front of the manual or the schematics.
• Test those transistors with the meter in diode mode; a shorted part reads zero or close to it.

Fix

• Replace the driver and its pre-driver as a pair; for a TIP36c also replace its TIP102 and small pre-driver.
• If the device still locks on with new transistors, replace the 74LS374: U2-U5 on WPC-S and earlier driver boards, U4-U7 on WPC-95 boards.
• After soldering, confirm all three legs connect to their traces; if the center leg is not connected to its 1N4004 diode trace, the new TIP102 fires once and then locks on and fails.
• Measure the coil afterwards: below about 3 ohms it is shorted from overheating and will destroy the new transistor.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• How a WPC coil, flasher or lamp driver chain works
• Where the WPC coil and lamp drivers sit
• Which transistor drives which WPC solenoid and lamp circuits
• The four groups of WPC coil outputs
• Fliptronics flipper coil wired wrongly
• Flipper energizes and stays up at power-on or game start
• How Fliptronic flipper drive works
• Electronic spares worth keeping for System 11 boards

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Two, Clay Harrell (pinrepair.com)