I find my Xenon rewards quite a few credits that I don't seem to have a way to turn off. If you max out the Mota wheel bonus and turn that light on, you will get a credit every second time you collect the bonus from then on. There seem to be other time it rewards with a credit that I don't know what it does it.

One main feature I don't really get is the red Xenon bonus special at the bottom of the playfield. What triggers it?

I will have to check my settings but I generally have it award specials as extra balls, but I still get the knocker hit while it adds a credit.
I have what I think are the factory settings for the xenon bonus. It stays lit at the 40k level and rebuild to the max of 58k, are you saying that is what lights the middle red xenon light? I have not noticed that giving me any extra balls, maybe that is my mystery credits.

In mine they will blink until the ball hits the shooter lane switch that is a few inches up from where the ball sits at the bottom. I put some really bright LEDs there so it stands out.

What rules do people set their Xenon up with? I generally use the factory settings for 3 ball, and set score thresholds to extra balls (door adjustment 16 set to 02) and playfield specials to extra ball on my old Ballys. But on Xenon, setting door adjustment 17 to 03 gives way too many extra balls. The Mota Special will give you an extra ball every second time you shoot the tube once you max the bonus. The Xenon bonus starts once you max the outhole bonus lights the 3rd time which is not hard since it maxes at 58k and drops to 40k, you hit 58k over and over in a good scoring game. For the longest time I have had setting 17 at 01 (gives a credit) but wanted a little bit of gain, so I recently changed it to 03 so now I get a 50k bonus rather than an extra ball or credit. Xenon seems more unbalanced this way than my other games.

To join this club, you have to beat my high score. Just kidding but I find Xenon's rules a bit odd in that once you max the Mota Wheel bonus you either get a ton of credits or constant extra balls depending on how you set the rules.

That sure looks like an original Bally capacitor on that switch. I would start there.

Question for Vec-tor, I never thought of the diodes or transistors as contributing to the Bally phantom firing issue. Is that a known thing? The caps for sure.

My Xenon has the same issue at the tube entrance too. I also have the ball get stuck sitting on the top edge of the targets at the right, usually on the second or third targets. I have not really found a good solution to either issue.

For your flipper, I assume it is not mechanically binding. Try yanking on the solder joints in case that makes a change. Try shorting out the EOS switch and see if that makes the flipper has full power (don't hold the flipper button in that state it will quickly overheat). If that helps you can temporarily clean those contacts to get it working for a while.

A single speaker does not require a particular polarity. Plug it in either way.

The tilt light will operate whether you are playing a game or not so yours seems normal. Does it always show the same two credits or do you mean it adds two everytime you turn it on? There is a dip switch you are supposed to set to hide credits to make the free play function work. Have you done that?

You need to get into test mode to sort this out. Does the button not respond at all? Try unplugging the coin door connector and checking it is not corroded.

What does it sound like when it resets? Does it make a sound like one of the slam switches is hit? You can manually trigger that to check.
If so, I would ask if you ever have any false bumper or sling shot firings while playing, even if only occasionally.

If it silently resets like you power cycled it, chances are it is a power supply issue.

Check your 5V supply level and make sure it is not too low in case the new SDB is not working right.

Second the supply shop comment. It is a standard industry tube size.

We probably need a bit more detail to sort this out. Do you have credits showing on the display and the game won't start or are you at 0 credits and cannot add any? How did you add credits previously? If operating the coin switches on the door does not work then I would do a switch test in the diagnostics. Keep in mind the coin switch, start switch, and the diagnostics switch are all on the coin door and if the coin door connector is the problem, all these switches will not be working.