^^Agreed, do this first. Replace all of the original switch capacitors on every switch under the playfield that you see. Remember that there are some on switches that are not called out in the manual, so visual inspection is your best bet to start with. The original Bally ones are junk and will die eventually. When they go, they do all sorts of weird stuff. I got a bag from Taydaelectronics.com for my older bally games.

Here are the caps I've used without issue on my classic Bally and Stern games.
https://www.taydaelectronics.com/capacitors/ceramic-disc-capacitors/10-x-0-047uf-50v-ceramic-disc-capacitor-pkg-of-10.html
GPE sells some as well that will work just the same, as mentioned above.

For Xenon, the playfield should have caps on the following switches:
- All 4 pop bumpers
-The 2 left side stand up targets
-Shooter lane
-End of tube switch
-All 4 top roll-over buttons (note that this is not listed in the manual, but was there from the factory)

As @frunch mentions, make sure to get the ones in the cabinet as well such as the plumb bob.

To get the game working for now, just cut one leg of the cap on each switch. You may not register every hit on those switches, but the game would play none the less.

Good Luck!