It seems really strange that the in the 5x7 matrix of strobes/returns, you always have at least a couple of strobes and a couple of returns that work but others that don't. I don't even pretend to understand what happens in the chips and it very well could be a problem in one of those interpreting/transmitting the signals incorrectly.

When you say the switches work or not, are you using a DMM or the open/closed switch test from the Control Board? Testing continuity through a switch and transmitting a signal to the control board can be two different things. Do those two tests yield the same results?

Six problems without any commonality is hard to figure out, which is surely why you posed the question. You seem to know more about the craft of pinball repair than I do, but I would like to help brainstorm a possible fix if I can.

Do the wire codes match up for everything? We tend to assume that everything came out of Bally as it should have and nobody since has tried and failed miserably to hack through a problem on your machine. Plus, there is at least one confirmed error in the EBC manual that I am aware of. It is possible in my mind that you have one strobe that is dead and the wiring diagram for the switches in the manual is not correct. I (think I) can help you compare your machine to mine if you want.

I'm glad you got everything working. Do you think it was the caps or the clean/adjust?

In my EBC, the stuck switch test would register a closed switch whether the capacitor was good/bad or gone. Switches with bad capacitors are more likely (logically) to test like a closed switch while it is open instead of vice versa. Working capacitors are not involved with closing the switch circuit, but rather giving the signal some "oomph" for the first few milliseconds after the switch gets closed. Blown capacitors can short, which would make the switch test closed, but if they blow "open", the switch should still theoretically work as normal but not so sensitive to brief closures.

The reason for my line of questioning is that with so many switches not working, you could have just had a dirty machine that needed adjustment and had some angry capacitors (as was the case with my auction-bought EBC, but not quite to the extent you experienced). Hopefully, you don't have a situation where a prior owner used sandpaper or a file to clean the switches and you won't have a bunch of problems once everything is tuned up.

I agree completely. I'm not 100% sure what the clock rate is for sensing switches in a 6803, but it is probably 60hz. The machine might not detect a very short momentary switch closure because it only "checks" for a very short period of time 60 (?) times a second. The capacitor adds amplitude and probably more importantly duration to the signal that the control board gets to indicate a closed switch.

The drops don't need caps, but the targets behind them will work more reliably with good caps. Lane rollovers can probably go without caps but rollover buttons will miss some hits if the caps are dead or missing.