I recently got a Doctor Who machine in generally fine shape, but there is a problem that is driving me crazy. Most of the time, it doesn't successfully begin the W-H-O sequence. All lamps and switches are working properly; when the ball goes up the right ramp (W is lit), the machine knows that the ball has entered there, and the HANG ON lights up...but not the "H" (though the H lamp will light as part of various display sequences). And when the ball is sent up that chute, the switch identifies that the Hangon had been made, but the W-H-O does not continue and the O (top ramp) light. However, every now and then, it will start work fine for a while, and then stop. I looked for any poorly seated jumpers or chips, and haven't been able to find any. I'm not an electrical engineer, and don't know how to identify any errors in the solid state components or their programming! This unit came from Europe and was converted back to US, if that is at all relevant. I'd appreciate any suggestions. Thanks!

Yup, tested all switches with a ball, tossing it through the ramps where I couldn't reach. (Actually, not all lamps are working; the whole ESCAPE bank is off, but I figured that is something different and will get to that next.)

Okay, so I pulled out and reseated the jumpers on the power driver board, and checked all ICs looking well seated and it worked for a while. But then it stopped working again. Yes, I did test14 (the miniplayfield, right?). And did a factory reset too. It doesnt seem to be obviously associated with temperature (my other idea). So it recognizes that the W-H-O cycle has started when the ball goes up the right ramp, but the H lamp (which works) does not come on. Seems like it's something wrong with its brain...

hmmmm... the PDB does not seem to be very hot; I am not sure about how to check the voltage regulator. No corrosion on the CPU board. But I didn't mention that there is a buzzy squeal, rather quiet, that is definitely associated with the display screen (it changes with the screen). It sounds like a ground hum that screens often have. It is plugged into a three prong outlet, and at one point, an electrician checked that the outlets were properly grounded, though the house is super old....

Okay, tried that, 4.97 on the PDB test point, 12V Test point also checked out...and yes, the flashers do work in test mode....

I think that was it! Thanks so much for pushing on that, aroden. I was too confident of the results of a single test. The housing for switch 37 is a bit loose. Usually when I test it, it works, but when the ball comes around the bend, if the housing has shifted, it can scoot past the wire. Bending the wire seems to have fixed it for now. But it doesnt seem possible to tighten the housing -- those screws don't seem to go into anything fixed.

Assuming that was indeed the problem, let me ask about the other major puzzle: all the ESCAPE lamps don't work, although the bulbs look fine; I replaced one with a new one to see if it made a difference. It doesn't. They don't go on in Test Mode, nor in General Illumination. Is there something obvious I can check? The ESCAPE switches all do work....

Thanks again!

Okay, maybe I'm missing something -- I took out the board with the bulbs, took out the bulbs, and tested all the solder lines for continuity, and all had it. I don't know if there is anything else I should look for there? As for the connectors on the backbox, I did look, everything seemed fine. But also, lamps 17 and 18 (left drain and return) work, so that means it isn't J137, right? Can you let me know what it means to "ohm it out"? I'm sorta new at this....
thanks!

Ok, arolden, you are two for two. Pressing gently on the middle of the board causes the connection to be made. I tried just loosening the attaching screws in case they were bending the board down, but that didn't fix things. So I guess I just try to remove and resolder the connector? Thanks!

Great! Will do. Thanks again.