What about the optos?

I have no advice on the cpu stuff (far beyond me). But I'm wondering if it's something more basic like a bad opto.

The one at the base of the MPF that reads the cam position.

Run a switch test and try it out.
faz

If you have the playfield glass out, the safety interlock in the upper left corner of the playfield will disable the mini playfield. Don't ask how I know that tidbit.

Did you ground the inputs of U2 with everything connected?
Those inputs are the data lines D2 and D3 and if you ground them, it would also drive lamp-matrix and other solenoids.
Did something like that happen ?

Possible bad connection on asic U9 or bad U12 on CPU board.

To be more clear, I was not asking to ground U2 inputs but was more surprised that you tested the Powerdriver this way.

A simple and quick test to see if all data lines are transferred from U12 CPUboard to the Powerdriver is a lamptest T9.
If all lamps are flashing on and off, you can be sure that D2 and D3 are working.
And if all is working + replaced Powerdriver, it is likely a problem with the miniplayfield itself. Maybe switch for the position of MPF.

Let me take a stab at this. Is it a rottendog powerdriver board? I had this same issue and it turned out to the that the data and power pins were backwards on the connector. Swap the wires on Pins 3 and 4 of J122 and see if the problem goes away.

Had exactly the same issue and due to the fact you say it drops a little at the top leads me to believe you have an alignment issue.

Refit the shaft of the motor onto the arbour - make sure the two grub screws are nice and tight. What is happening is that the assembly is probably slipping or slightly out of alignment on the flat of the motor shaft as it turns. Then the opto triggers but it is probably a few milliseconds outside the normal range and the machine thinks there is an error.

I temporarily fixed it by aligning and retightening but the shaft had a bit too much slop in it and i ended up having to replace the motor and gearbox. Very frustrating problem to find as everything tests fine like you have described.

Bumping an old thread to see if the OP managed to fix this issue.

I am having exactly the same problem, where the playfield will not move clockwise, but can move counterclockwise. The motor moves up and down just fine with an external power source. No binding or scraping when installed into the cabinet. However, it cannot move back down after raising the playfield in gameplay, and all CW tests fail in test mode. However, there is some strange behaviour in test mode. During the CW tests, the playfield will do nothing, but will then move counterclockwise for the last second of the CW test.

I have checked the optos - all good. Power driver board is known to be working. I just rebuilt the entire mini playfield from the ground up, so there is no issue with old grease. The motor works properly and the gearbox has no stripped gears.

Also like the OP, the playfield drops a little bit when it lowers to the second level (the mushroom buttons).

In response to robm's post, I have just made sure that the grub screws are tight on the arbor. No slipping.

I am tearing my hair out with this issue. Any help is appreciated.

Here is a video showing the behaviour:

Note the lack of CW movement, but good CCW movement. Also note the way the playfield drops slightly when lowering to the second level.

Wow, I feel like an idiot.

All fixed now. The wiring from J122 to the motor driver board was incorrect in the manual, so I "fixed" it. The wires going to the motor board were reversed. Turns out, the manual is actually wrong, and these wires are meant to be the "wrong" way around.

So the moral of the story is: if it ain't broke, don't fix it.

Good news, now go play

Bumping this up because I was getting the "No CW Movement/No CCW Movement error" and had another cause not mentioned here--wanted to include it for future searches. Turns out it was an issue with the bi-directional motor board under the playfield (Bally/Williams part number A-15680/A-14768). A capacitor had burst, causing the problems. New boards are available at Pinball Life and Marco:

https://www.pinballlife.com/bi-directional-motor-drive-board-for-ballywilliams-machines-a-15680a-14768.html
https://www.marcospecialties.com/pinball-parts/A-15680