Quoted from PhillyArcade:
Question, my MB is rebooting whenI first fire it up. The first few games you'll play a little and the game reboots. I'm thinking caps? One way to make it happen is multi ball or hitting both flippers at the same time. Good place to get a rebuild kit for it? I see Marco sells one.
This sounds like a 5v reset which is a common error on WPC & WPC95 machines and is well documented.
A quick (temporary) fix is to use a Kahr board https://www.kahr.us/daughterboard.html
However if you want to troubleshoot and address the issue (which it sounds like you do) then the below will help - the majority of the below is word-for-word from "Repairing Williams/Bally WPC Pinball Games from 1990 to 1999" but it has some additional comments on pin pointing the problem that I found most useful. It's basic troubleshooting but broken down into the steps and well explained.
"+5 volts DC: TP2 (TP101 on WPC95). Should be 4.92 to 5.1 volts DC. If this is below 4.92 volts, the game will most certainly reset easily, as this is the voltage the "reset watchdog" examines. Often the problem is bridge rectifier BR2 (diodes D7-D10 on WPC95) and the related filter capacitor C5 (C9 on WPC95). Sometimes it could also be the +5 volt voltage regulator is failing (Q1 LM323K or LM317 on WPC95). Or it's very common for the input connector (J101 or J129 wpc95) or 5 volt to CPU board output connector (J114 or J101 wpc95) on the driver board. At this point do NOT remove/reseat the connectors!
This is very important. Removing or reseating the connectors will make finding the actual problem nearly impossible. So don't touch them yet!
Check for +5 volts on the CPU board. Yes I know, you checked the +5 on the driver board TP test point. But there are *two* connectors (or sometimes a third/fourth "Z" conector too) that go from the driver board to the CPU board. If these connector(s) are having problems, the +5 volts will be lower on the CPU board than it is on the driver board. The best place to test for +5 on the CPU board is right at the CPU board game EPROM pin 32 (the last pin). If the CPU board's +5 volts is even just a bit lower than the Driver board's Test Point +5 volts, that means the connector(s) between these two boards need to be re-pin'ed with new Trifurcon connector pins. This is very common and just re-pin'ing these two connectors can fix a lot of reset problems (without having to change any driver board parts).
Next reseat the right side driver board connectors J101. Power up and re-test the +5 volts on the driver board Test Point. If the voltage has gone up, then the input connector J101 is bad. Repin this connector with new Trifurcon connector pins. If it's the original connector (IDC), you will have to replace the connector housing too.
Recheck the voltage on the CPU board at the game ROM pin 32. Now reseat driver board connector J114 (J101 on wpc95) at the lower left. Recheck the CPU board +5 volts at game ROM pin 32. If the voltage has gone up, connector J114 needs to be replaced. Repeat this procedure for CPU board connector J210, and then repeat with the "Z" connector (if the game has one). Again if voltage changes after a connector reseat, the connector MUST be repinned with new Trifurcon connector pins. (And wire brush the male connector pins or replace them too.)
If the CPU and Driver board +5 volts are very close to each other and are 4.92 volts DC or higher, try this. Remove driver board +5/12 volt connectors J114 (power to CPU board), J116 (cabinet), J117 (backbox), J118 (playfield), and measure the 5 volts at TP2 on the driver board (on WPC95 connectors J101, J139, J138, J140/J141 respectively). If you still below 4.92 volts, BR2/C5/C4/LM323K regulator are the likely culprits. If the +5 volts goes up with these four connectors removed, one of the other boards/devices is dragging the +5 volts down. Replace the connectors one at a time to try and find the culprit."