TP2 and the CPU board 5 V agree with each other but both sit low.

Finding a board or device that drags the +5 V down

Cause: Either the 5 V supply parts (BR2, C5, C4, LM323K) or a load on the 5 V line.

Checks

• Unplug the driver board 5/12 V outputs: J114 (CPU), J116 (cabinet), J117 (backbox), J118 (playfield); on WPC-95 these are J101, J139, J138 and J140/J141.
• Measure TP2 again. Still under 4.92 V: suspect BR2, C5, C4 or the LM323K.
• If the voltage rises, plug the connectors back one at a time to find the device pulling it down.

Fix

• Replace the failed supply parts, or repair the board or device found.

Systems

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

Related tips

• Reboots at start-up and when flipping: flaky power connector to the CPU
• Game keeps resetting during play: poor J101/J102 power connections
• Resets when a drop target or coil fires: burnt power and GI connectors
• Game reboots the instant the second visor lock is made in later multiballs
• Resets when the knocker fires, hum and DMD glitches: cracked power board joints
• Resets during the Powerball battle: reseat J101 and J115 on the power driver
• What a WPC game reset is
• Watching the supplies while the game resets

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