I was really hoping I could do this one myself. Digging through Clay's guide, I'm at a loss where to go next.

Coils are not behaving.

All TP test per spec on MPU and Solenoid Driver Board
48.1 V at both lugs of all coils

But...
ball launch coil will not fire
lower(center) popper swich fires left sling kicker coil, lower (center) popper coil does not fire
left(upper) poper switch fires RIGHT (upper) poper, left (upper popper coil does not fire)
right sling switch activates drop reset, right sling kicker does not fire

right(upper) popper switch fires right (upper) popper coil [correct function]
Left sling switch activates left sling kicker [correct function]
knocker works

In test, left (upper) and center (lower) coil do not fire. Right (upper) coil fires twice.
saucer eject coil works
both flipper work

Clay's guide specifically calls out my issue..explaining the cause, but these are what I would call "fun facts". Any clues on how to fix?

Quoth the guide...
"Wrong Coil (or No Coil) Energizes.
This is an interesting problem that isn't very easy to diagnose. For example when a slignshot
switch closes, the drop target bank resets. Or perhaps one particular coil never engergizes in
the game.
This is often due to the PB0-PB3 encoded lines that come from MPU PIA U11 or the line
select. These four bits are encoded by the PIA, sent to the Solenoid Driver board (SDB), then
unencoded by the SDB U2 74154 chip, and the appropriate solenoid is energized. If one of
these four bits is lost in the data path between the MPU and the SDB, the unencoded number
will be wrong, and the incorrect solenoid (or no solenoid) is energized.
Another test of this problem is to put the game in coil test. If coil(s) fire twice (same coil for
two solenoid numbers), or does not fire at all, there is potentially a problem with the
PB0-PB3 encoded lines."

I should note, the game was working just fine. One day, it stopped working.
TIA,
faz

Well, I feel silly.

I tore through Clay's guide and saw the part about checking J4. But since I was in solenoid mode...I was working with J4 on the solenoid board.

I saw your note and said....OHHHHHH the "MPU" board.
Nuts... I was traveling last week; I just had a chance to try it out.

A quick reseat of the connector ...and it all works fine.

I pulled the connector again and gave all the pins a brush with some 600 grit paper. All good.

I don't have any pins...I'll order some with my next parts order.

Thanks for the note...you got me in the right direction!
faz