I get 41VDC on my Taxi (System 11B as well) ...so I think you are o.k. there.

Hmmm, might not actually be a problem...take a close look in the pg 35 in the manual at how this test operates. I have to depart now, I'll be checking back on this thread later.

1)Fuses F1 and F3 are tied together at only one end, if one blows, the other still conducts current. This is a function of branches in basic electronics. Page 96 power wiring diagram shows the fuses on the right side of the aux power driver board and denotes which solenoids each protects. From your solenoids indicated, they should not be on when F3 is blown. Perhaps there is a miswiring or short to an incorrect solenoid. Just a guess at this point

2)Blanking LED should be on - solid on. If it's out - either a blanking circuit problem or dead LED itself. I'd lean toward the LED simply being out if your score displays are coming on and she boots up.

3)Questionable behavior there. Maybe an upper level logic problem?

4)If you are getting a bunch of coils firing such as the knocker, and locking on - that's not good. If a ball is not found such as due to a bad switch indication, the game may sequentially fire playfield coils to "look for the ball". But they should never lock on. Having such a large group of solenoids lock on occasionally is a good indicator of logic circuit problems on the MPU. Not really a beginner type of repair.

I would go through the power supply thoroughly to make certain it is in specs before doing anything else. Has this MPU ever had any battery leakage or evidence of corrosion? This is a tough call, I don't want you to get too alarmed, but I think you might want to send this board in to a pro for diagnosis and repair.

The "random occurrence" of firing all coils: I don't agree that this is normal thing. IMHO, My first suspicion is that is power supply related. I have three System 11s and I have never had that happen. However, I have not researched the documented cases you are describing.

Since you have confirmed battery leakage in the past, I would be highly suspicious of lingering damage - especially what you can't see. That stuff creeps into the legs of IC's and can wreck them internally. It could look clean on the outside, but the damage is done. I'd be really suspicious of the PIAs nearest the battery holder (such as U41,U42) if I had to point a finger, or the fine traces under the pack. Just some hunches, though.

The Six PIA's and What they Control.
U10: Sound output selects, solenoid drives, CPU board flipper relay K1.
U38: Switch matrix columns and rows, special solenoids A & D.
U41: Score display data (1J22), special solenoids B & C.
U42: Sound board (1J21)
U51: Score display circuit (1J1, 1J2, 1J3).
U54: Lamp matrix columns and rows, special solenoids E & F.

Perhaps you might try replacing the PIAs first. Leon's guide might help if you want to DIY. Troubleshooting this kind of problem gets even more complicated when the board doesn't do the same thing every time it is powered up. Good luck.
http://www.system11.org/tech/system11_cpu.html

I'd recommend to send it to one of the pros here for an evaluation. Alkaline damage on System 11s is always worse than it looks. I've repaired a lot of Bally boards dead from corrosion, and usually pass on damaged Sys 11s. You could also replace the board as a last option.

I think you will need the test ROMs to do this:
http://pinwiki.com/wiki/index.php?title=Leon_Borre_Williams_System_11_Repair

When testing a BUSSED resistor network, first find pin 1. This pin will have a white square around it, to isolated it from the rest of the pins. Use a DMM set to ohms, and put one lead on pin 1. Put the other lead on each pin 2 and up. The same reading should be seen for each pin 2 and up. Note "in circuit" (resistor network installed in the board) some networks may have pins that measure differently than the other pins (for example, pin 10 of SR17 which measures about half what the other pins measure). Out of circuit (resistor network not installed in the board) all pins should measure the same.

When testing an ISOLATED (discrete) resistor network, put the DMM leads on the two adjacent pins furthest to the right or left, and note the reading. Then move both DMM leads down two pins. The same value should be seen. Continue down the resistor, moving both DMM leads two pins at a time, until all adjacent pins are tested. Again note "in circuit" (resistor network installed in the board) some pins may measure differently than the actual value. Out of circuit (resistor network not installed in the board) all pins should measure the same.

Note: Testing resistors/capacitor networks "in circuit" is may not be conclusive. A bad resistor network which is soldered into the circuit board can test as "good", but in fact be bad. This does happen (but pretty rare). My advice is this: if the resistor network tests "strange" (as shown below), probably best to replace it. Note SR9, SR10 and SR11 are the most commonly failed resistor networks in system11 CPU boards (but luckily these are easy to test in-circuit). The SRC resistor/cap SIPs are a bit more tricky to measure in-circuit.
http://illinoispinball.webs.com/williamssys911part3.htm

Earlier in the post he stated "verified all voltages coming out of the power supply as good"

What exactly did you measure? Should be around +5VDC +/- .3 VDC @< .5 VAC AC ripple?