I have run into an interesting issue. Tri Zone, left pop bumper coil gets hot, was the report. So I immediately figured, bad transistor. Easy fix. Nope! They had already replaced the MPU and SDB with a new Rottendog combo unit and have the same issue. I checked a few things, replaced the switch diode, for good measure too. All coils, minus the one that over heated, test ok.

The cooked coil, I measured the voltages that would be going to it. It has a solid 12 volts all the time. On top of that, it's power pulses with every coil that fires. So it tries to fire as well. My current thought is, the lighting circuit must be shorted in line with this, but I couldn't find anything anywhere.

Any thoughts?

#2 4 years ago

237

slochar

Pinside member

7y 86,550 6,913

There should be coil voltage on both lugs of the coil and the special solenoid circuit grounds it to fire it. So your voltage is low should be about 28 volts.

You've got a sneak short to something in there that's for sure take the pop bracket out and suspend it in midair to check, then pull the switches as well, same thing. Disconnect the wires and measure without them connected to the coil, there should be 2 power feed wires and one switched wire.

The switch diode on a special solenoid is the bottommost switch for scoring only, has nothing to do with activating the pop. The activation switch (closer to the playfield, right up against the plastic spoon) doesn't have a diode on it although it might/should have a resistor and capacitor, which provide a minimum pulse to the special solenoid circuit (it's just a ground pulse) - they could be bad.

Oh, and suspect the pop lamp, since its leads run right up against the pop bracket.

#3 4 years ago

RJW

RandyW

Randy's Pinball

Maryville, TN

11y 94,800 1,305 18

Thank you! I will dig into that!

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