Okay, I've got a Dr. Who that has been sitting in the basement for a couple of years. Decided yesterday to turn it on and see what happened... Got the "factory settings restored", which I expected, as the batteries haven't been touched. Also, as I was going through the tests, the machine would keep resetting. I'm guessing something is taking down the 5v, but as I was doing a quick check on stuff, there was a sudden sparking over by the audio board/fliptronics board area. Quickly turned it off, and investigated to find this on the audio board:
C26 is exploderated! Any ideas what I should be checking out next?

-Brian, off to find the correct schematics for the audio board.

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Yeah, I ordered new caps and they arrived today. I'll replace them and then resume troubleshooting the 5V.

-Brian

I imagine there's enough going on during multiball that if your 5V is getting weak, this is when you're most likely to get resets.

Looks like he’s back as of this morning...
Really enjoying watching your progress!
-Brian

Got some time to work on my Doctor Who this week, got the mini PF taken out. One of the target optos is dead, and another one I think is really close to dying, so I plan on replacing the boards... pinballinreno - how long did it take for your set from PindoraBox to arrive? I think that's the ones I am going to go with. Are the receivers short enough that you didn't have to shave them down or anything? I may also spring for a new opto carrier from swinks, those look pretty stout!
I had a problem with my controlled lights, but that's figured out now. Once the MPF is done, I should be fully operational. That's going to be nice, I haven't played this game in about 6 or 7 years!

Alright, got my opto boards ordered from Pindorabox, and the new style opto carrier from Swinks. Now I just have to wait for them to arrive... I will spend the interim getting everything else on the game in good order, and waiting to finally have my machine working again!
-Brian

Mine is currently disassembled. I will get down to the workshop tonight and get what you need.
-Brian

Looks like I came up with the same thing you did...

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Ooh! I checked my mail today, and not only did my swinks opto carrier arrive, so did the pindora opto boards! Looks like I will be playing soon!

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Thanks for the tip. I think I may have some sitting around...

I don't envy you... Good luck!

Alright, making progress! I soldered on my new Pindora PCBs and transferred my mushroom targets over to the new Swinks carrier. I used a piece cut from a sheet of packing foam stuff (like new electronics, such as a Blu-Ray player or something, come wrapped in) to space my receiver board. I REALLY like this opto carrier, it's SOLID. The light baffle things between each opto set is great, and it definitely adds to the structural integrity of this. I don't think I will ever have to worry about this thing flexing or changing shape and changing the alignment. I plugged in the connector to the game and was able to verify the function of my switches after a bit of fiddling. I did have to put a little bit of shrink tube on each of the receivers, as they WOULD NOT interrupt without it. (I neglected to take any pictures of this.) Just long enough to cover most of the side of each receiver. All but opto SW72 are working great...
SW72 was not working at all before i installed the new components, and still isn't working. I verified continuity from each of the termination points on my PCBs (A4/E4) to the opto board under the playfield, as well as continuity of each pin on the 10 opto board connector J1 and J2 to the first resistor in the circuit. All resistors showed the same value, and each junction point of the two resistors that goes to the U1/U2/U3 (-) pin shows continuity. All diodes check good, as well as continuity from each diode to the J3 connector. So, I guess my U1 chip is bad? Am I on the right track?
Thanks!
-Brian, getting closer...

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Yes, I have done this.

This is how I started, just to prove if the pairs worked. I could get all of them to show a signal except SW72. This was also the case with my original 5-opto PCBs. I didn't put the shrink tubing onto the receivers until after I proved I could get the switches to show both clear and blocked (with the exception of SW72, which always showed blocked). I was unable to get any of the working pairs to show blocked without the shrink tubing. 4 of the 5 mushroom target switches are working perfectly now, but I have not been able to get any signal from the last one. As I said, this was also the case before I started working on the MPF. This leads me to believe that the problem is not with the 5-opto LED/receiver PCBs, and is somewhere upstream, i.e, the 10-opto board.

I will try verifying transmitter and receiver tomorrow before I get into swapping the IC on the 10-opto.

Thank you for your help!

-Brian

Tomorrow I will also jumper the pins during the switch test and see what happens. And I just checked my stash of ICs and discovered that I DO have a LM339 on hand, so that's a good thing, if I need it...

Success!! I replaced the U1 chip, put the 10-opto board back in, and now all of my mushroom targets work wonderfully!
Now to put the mini playfield back together and install it, and make sure it goes to all three positions properly, and my game is ready to play. It's been a loooooong time, and I'm really looking forward to it.
Thanks for your help pinballinreno !

This is what I did (pulled them one at a time from the original boards and transferred to the new ones). I did notice that the Pindora boards were screened wrong after I had transferred the wires...

Actually, once I got them working, I did not bother to remove the sleeves. I imagine I could, but they're working, and I didn't want to tempt fate.

My MPF home opto wasn't working at all, and I finally figured out that I have a flaky connection on the small 2-wire Molex connector from the MPF to the harness. Everything checked good continuity from the opto to the connector, and from the other end of the connector to the 10-opto board, and from the 10-opto board to the backbox, but when I plugged it in, no continuity. I ordered new connectors from Ed at GPE, and also figured I'd get a few replacement opto LEDs and receivers as well. They arrived today, and I will continue working on my machine later this week when the weather is more suitable to work inside - too much to do outside right now!

I'm almost there, getting there slowly!

-Brian

I would consider getting in on this if it happens.