It's more of a thump than a knock. With the door closed I barely hear it, with it open it sounds like a rubber ball on the ground.

***KICKBACK***
My kickback seems weak.

Yup. Mine typically fires the ball gently into the POWER targets... sometimes it catches just right and hits the 5 or 6 target, sometimes it ends up right in the right outlane.

Keep in mind (for both the knocker and kickback) these are NOT the 50V coils of a system 11 game. Williams were I believe the last ones to adopt high voltage coils.

***JET BUMPERS***
My top two jet bumpers fire at the same time. Underneath the playfield someone has jumpered them together, but I can't imagine why.

Probably because either wires broke, or something failed in one of the switches causing one not to operate well on its own.

Keep in mind power is daisy chained (I'm not saying your setup is or is not correct yet) from coils all over the game (I think it's blue wire on FP?) My guess without looking at a wiring diagram is that your pop bumper issue and your slingshot issue are related. By stealing power and ground from another pop bumper, the previous user may have inadvertantly disconnected the slingshot power.

***Right slingshot***
My right sling shot is dead. How do I measure voltage? Do I have to have the machine in test? What else should I check? All wires look like they are making good contact.

DMM set to something like 200V DC. Put one lead on the power lugs of the coil and the other lead on the ground braid in the cabinet. Should see ~30V I think? You can also try manually grounding the coil with a jumper wire from the GROUND side of the coil. Do it quickly don't hold it on - and don't ground the power side of the coil. If the coil fires, you have a switch problem. If it doesn't, fire but voltage is present you have a coil problem. If there's no voltage, you have wiring issues.

***Strange lockup***
Today I replaced the caps on my power supply. Now I am getting random lock ups. Does this sound like a connector issue? I will be changing these eventually, but haven't yet. Or could one of my new caps be causing an issue? Or since my ROM chip is rigged because I broke a leg off and am waiting on the replacement, could that be causing intermittent issues? When that pin wasn't connected the board was simply dead until I rigged it. Not sure if there is change in resistance or anything because I have a jumper wire on one leg.

Could be any of the above. The 40 pin can cause all sorts of problems - replace it. Are you sure your new caps are correct? You could be getting AC noise into the 5V line if the caps are imporoperly installed or are the wrong values. A poor connection on the ROM chip or any socketing could also cause it.

Reflow the solder on the headers if you don't replace them.

One thing you can try is carefully physically pushing on the boards and flexing them to try and cause the issue. It seems silly but it often works to find cold solder joints or poor connectors. You only need to have the 5V line cut for a fraction of a second to confuse the game. A bad solder joint or a flakey ROM connection could easily do that.

I noticed in your video you had the game boot up in audit mode as well - this is either a battery issue or a RAM issue. If your RAM is flakey it may or may not help cause a lock up - someone else would have to chime in on that one.

Yeah don't set freeplay if it boots into audit mode. Frustrating to have that disappear every time