Start by reading the tech docs. You're an electrician so I assume you have access to a DMM/voltmeter. You'll have most of the tools as well, but you may need some specialized ones as well, also listed in the repair docs. The game is probably going to need repairs and mods to several boards and cinnector overhauls as well.

http://techniek.flipperwinkel.nl/ballyss/rep/index1.htm

Yes, but that won't cause a lack of display characters, just prematurely burn out the display. A lot of these old Bally's are over voltage, and still run. When you get one, you should rebuild the HV and adjust it as far down as comfortably viewable to extend the lifespan of the gas displays.

Easy there! Start by SLOWING DOWN. I know you are excited, but you need to gain some education non how these pins work before you dive in. If you move too fast you will cost yourself more time, more troubles, and more expenses that are unnecessary.

Coils actually rarely go bad. A solid state pinball is more like a computer. Read those docs, start to learn the diagnostic menu (if it gets that far) and start learning how to use a meter to check.your basic electronics. The first thing will be testing, modifying and making certain the power supply is performing within specifications and stable, then you can address issues with the rest of the systems.

If you are going to quote someone, make sure you quote the right person. I said exactly what you are saying now in post #7. There is a minimum voltage required to make the glass glow, and rebuilding and adjusting the HV may still be necessary.

From your post it sounds like your boards are hacked. I would go through each board performing the recommended repairs, modifications and overhaul systematically, board by board and repin all the connectors properly. Read all of the docs and check each board thouroghly

http://techniek.flipperwinkel.nl/ballyss/rep/index1.htm
http://www.pinrepair.com/connect/

Post a pic and we'll tell you what we think. The Alltek is a good option. For someone with experience, repairing a corroded board is labor intensive and about $20 in parts....but it's still somewhat a gamble. You could end up replacing more parts, or having more headaches. Replacing the board will help you get the game up and running quicker in most cases.

It could be reparable, I've seen worse. Did you read the tech docs I linked to in the first post? Damaged components need to be removed, acid neutralized, traces sanded clean and repaired where necessary, and then new components installed. You can get the parts from GPE or Big Daddy. It's a bit if work and involves replacing about 20-25 components. It's not a beginner task, for sure.

Switches are daisy chained, and it is very common to have a broken wire on a row or column switch that is upstream from the malfunctioning switch. The upstream switch will still work. You'll have to visually follow the wires from the malfunctioning switch to the others in the same row/column.