The voltages you are reading are actually pulsed, so the only completely valid way to test them is either with a scope or logic probe. If the signal is locked on (rather than being pulsed) you will get high readings.

Since the reading you get when using a DMM on a pulsed circuit can vary wildly, depending on the quality of the DMM, it is impossible to say if 12.5 volts is ok. About all you can get with this method is relative readings when comparing different circuits. I would check all of the column readings at J206 and see if they read the same.

Since U20 (column driver) is blowing I'm not sure the row voltages are even relevant since there is a blocking diode on each switch. Although something could be over-driving the chip.

Which columns quit working when the IC blows? At the moment I would be more suspicious of high voltage getting shorted to one of the columns.

Sorry about the type, yes J206/207.

Firing all of the solenoids in test would be a good start.

Sounds like you're on track. Just keep narrowing it down.

Good thought LOTR_breath--it is a weird problem.

Could be a partial short on the row side of one of the switches or the row circuitry on the board. I would pull the row 8 wire at the cpu row connector, close a physical switch (not an opto) and see if the voltage drops. If it doesn't then it's a board issue.

Let's take a step back. If you're blowing U20 then you've got high voltage shorting to one of the columns. If you still have the defective U20 you can test it the continuity across it and possibly identify which column. Check from each pin on the IC to the ground pin for a short.

Not as much help as we would have liked. Pin 10 being common is kind of misleading--just means that once the high voltage came in on a row it also shorted out the 12 volts to ground.

I was hoping to only see one column pin blown out and then we would know more specifically where to look.

pin 11 -- col 8
pin 12 -- col 7
pin 14 -- col 5
pin 16 -- col 3

Do any of those columns coincide with any rows where closing the switch seems to cause problems?

One shot in the dark thing would be to check the pop bumpers for any bare wires or leads that could be shorting high voltage to the switch matrix. I suggest that only because I've seen the issue be pop bumpers quite a few times.

I'ts not grounding a column, high voltage is being shorted to the column. I doubt if a switch could cause this issue.

When you have an intermittent short like this there's not a lot of classic troubleshooting (i.e. - taking voltage readings) that you can do. It really comes down to inspection or narrowing down the possibilities. Based on the way the chip blew we can presume the problem is on column 3, 5, 7 or 8.

1. Go through all the switches in those rows looking for a wire or lead that could be shorting to high voltage. Move any nearby mech's by hand since they could be moving a wire and causing the short. While I'm at it I move every diode lead or wire as far away from anything else as possible.

2. Pull the column wires for 3, 5, 7 and 8 and see if the problem goes away. Then add one back at a time until the problem shows up again.

3. You could go into switch test and start closing switches and see if U20 blows. Because of your symptoms I am suspicious the high voltage short is on the row side of the switch rather the column side. Thus the switch has to be closed for U20 to blow. This might help narrow down the issue (this is what I was trying to say above, but didn't word very well).

Chris or zaza, if you're still watching do you have any other ideas?

Could be wrong, but I think the voltage readings are just confusing the issue. In order to blow the chip out like you're seeing it is most likely high voltage shorting to the column. There could be a high resistance short from high voltage to the column and then due to vibration, assemblies moving, etc. the short becomes low resistance and boom your ic is toast.

At the moment every switch is suspect. You really need to narrow the issue down to a column and then you've only got 8 switches to worry about. Sometimes you just aren't going to find it visually.