Random resets, with the +5 V test point on the driver board reading low (for example around 4.88 V in attract mode).
WPC-89 resets on low +5 V: replace the small 100 uF 5 V filter caps
Cause: The small 100 uF 10 V filter capacitors on the +5 V line dry out. One measured just 16 uF with over 40 ohms ESR out of circuit, which drags the 5 V line down. Later WPC-95 boards use 25 V parts in these spots.
Checks
- Work through the standard reset checks first: connectors, cracked header pins, cables.
- Measure +5 V at the driver board test point in attract mode.
- Check the ESR of the 100 uF caps at C4 (driver), C31 (CPU), C3 (early sound board), C3 (DMD controller) and C1 (Fliptronic board); good ones read well under 2 ohms.
Fix
- Replace all of those 100 uF caps with 100 uF 25 V parts, before changing the big C5 filter cap.
The driver board has large filter capacitors and transformer voltages; unplug the game before removing it.
Systems
Related tips
- Resets: +5 V at the driver board test point is low
- What a WPC game reset is
- Resets remain after rectifiers, caps and connectors are done
- Reboots at start-up and when flipping: flaky power connector to the CPU
- Watching the supplies while the game resets
- WPC CPU board LED meanings
- WPC CPU board LEDs at power-on
- Reading the CPU board LEDs at power-on
Source: Pinball Repair help group!! (Facebook group)