I'm so friggin happy right now. I just took apart and put back together the mini playfield on my Dr Who. Since I bought it, only 2 of the 5 optos on the mini playfield were registering. Major problem, as these 5 targets are the main point of the game. So today I took it all apart and installed 2 new opto boards that I bought. 3 or so hours later and a few cigarettes for stress relief, I put it into test mode and it friggin worked! All 5 optos register now!!!!!
I also cleaned the clear sub sump underneath which was filthy, and changed 15 555's that sit underneath the ramp, you can't get to them with the ramp on. I also changed all the rubbers/bulbs on and around the mini playfield that are normally impossible to get at.
Here's some pics and a link to the repair guide that helped me do it. I've done some soldering, replacing switches, fixing minor problems, but this was my first MAJOR repair.
Photos
http://www.flickr.com/photos/tomdotcom88/sets/72157622391176356/show/Mini Playfield Repair guide
http://members.shaw.ca/tomblack/drwho%20miniPF%20repair.pdf