Issue #1and #2 usually bad connector pins on MPU, J206-3, check for corrosion and broken wires, but still check optos

So look for 2 wires, black and red, that would be attached to a small motor on the time expander. If you raise the playfield to the full upright position, the min playfield will be exposed and the motor should be visible along with the wires. If one has broken off, their will be no movement, or the plug itself is unplugged

It sounds like it had movement, so I'm thinking more a connector issue. As eyeamred2u said, the red/black is power to the motor, but the optos control the stages and where the CPU thinks it is.

Step1) do a full test of the whole machine of the basic functions. Inventory what works and what does not. Every switch, solenoid and even the flashers. Test the switches with a ball, not your finger. A few non-sequitur switches not working could indicate a matrix issue.
Step2) If you get it moving again, try running TEST 14 to run the MPF through it's paces. There's a lot of really good intel displayed on the DMD.

faz

Listen to pinball_faz ! He has a killer guide for the mini playfield as well. It was hugely helpful to me when I fixed up my Doctor Who.

Do as Faz has stated and all functions of the game needs to be tested. If their is a bad connection at J206-3, that MPF position is not going to be correct, trust me I know. I replaced optos in that MPF and finally tracked it to a broken wire in the J206 connector. J206-3 in the switch matrix is very critical to what issues you are having, so do not rule out the small stuff. Pay attention to the DMD as Faz says, if the MPF is not going to Top, Middle or Bottom, narrow down why. Dirty opto. Bad opto receiver. Broken wire. Let us know what you find, hopefully we can assist further.

I had the VUK problem you describe recently myself. I had switched the original Tardis over to a USB Tardis that looks nicer. However, after getting the same VUK problem. I started looking at probably replacing the Optos. However, what I found was that the green and white wire that goes to the blue bulb in the top of the Tardis was interupting (in between) the optos sometimes. With it Ty-wrapped away, the problem went away.