Hello,

Our Doctor Who Pinball's Mini Playfield has a problem. We are getting sensor errors resulting in the mini-playfield not operating correctly.

It has a new motor, new optics, the optics have been tested and work as far as we can tell (we did continuity tests as well, so the wiring is fine). When turning the machine on, the sensor light comes on, the receiver has been tested, but breaking the light does NOT trigger the register.

What do we fix next? Is this a chip problem, and if so, where is it?

On startup errors: Switch 15 (Left Sling), No Clockwise Movement, No CCW Movement.

On mini-playfield tests, the mini playfield WILL travel up and down (holding both flippers), but fails. The optical sensor again IS working, it IS lit, but the interrupt is NOT registering during the switch test (passing something between the sensor and the receiver). This leads us to believe that it may be a chip issue.

There are no aftermarket boards in the game as far as I know. We have had it for about 18 years.

View on Playfield on Youtube: https://www.youtube.com/embed/KF_LbUkAZ4M

Yeah, it seems to have changed on us since yesterday. Also, I posted a video link in the last edit, just for reference.

One of the other guys in the shop did the switch test a couple of days ago and we think we tested everything, but the opto sensor at the flywheel did NOT register when we passed something between it (again, it IS lit and all continuity tests came back positive on the wiring and soldering). I will do another switch test once the customer(s) leave.

RESULTS: So far, I have been unable to find any additional switch errors...

Okay, did the test of the switches and everything else works fine EXCEPT the Opto Sensor for the mini playfield flywheel.

I think I figured out why the error changed on the mini playfield during startup: the coin door was open (only gives one error code instead of two).

Attaching two images: 1) opto sensor confirmed working, 2) underside of the pinball table (feel free to identify any parts I should check).

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I unsoldered the new receiver and put the old one back on and it works now!

So, bad receiver from the pinball parts supplier.

The mini playfield's up and down motion is controlled by a motor that CAN become stripped in the gears if it ever "goes sideways." This happened on my unit when a screw fell out of the metal ball-catch when the playfield was up all the way and a ball went in. The playfield started going down and stripped the gears. It required a new motor.

If the opto sensor on the flywheel goes out (either the opto light or the receiver), the mini playfield will not know where to stop, resulting in errors.

If you remove the mini playfield and later put it back in, make certain the cables in the back are not crimped as they can impede the up/down motion of the mini playfield.

The only way to see if the opto sensor is working (without an expensive IR detection card) is through selfie mode on a cell phone. Get the camera positioned just right to detect the IR light (invisible to the naked eye). If you cannot see it, it is not functioning. It is either burned out or unsoldered.

BEFORE REMOVING YOUR MINI PLAYFIELD, READ THIS DOCUMENT: http://www.pinballsupernova.com/images/TheDoctorWhoMiniPlayfieldv1.2.pdf

PRINT IT AND PUT IT IN YOUR PINBALL MACHINE. You will refer to it often if you ever have to work on the mini playfield.

Okay, new issue. I had replaced the motor on the mini-playfied and everything was working just fine, but I was getting startup errors which I just looked at. It says my clockwise and counter-clockwise is reversed. Now, I soldered the new motor in the exact same way the old one was; does that mean the new motor needs to be soldered in the opposite way? Is this a serious issue? Again, it is playing, but I don't want to cause any long-term damage.

I have another issue. The far back bumper (near the 5th Doctor) will not light, even with new bulbs. Accessing the assembly from the top does not appear to help solve this issue, and underneath it appears there may be more causing the light to respond than simple wiring. What is the best way to repair the light inside the back bumper?