So it doesn't pulse, it holds in solid?

Well my number one guess would be the pop bumper switch. After that, bad 7400 series chips on the mpu. But if it were a board problem, it would do it all throughout the game. So I'm thinking switch is too close, and the shaking of the ball being "vended" is causing the switch to be made.

I had a leaf switch on my Space Station that was to close. It would sometimes randomly fire the left jet bumper and sometimes hold it and blow a fuse. I adjusted and cleaned leaf switch and have never had a problem since.

Oh and replaced fuse!

The special solenoids in whirlwind are not switch controlled (J18 is empty). They are CPU controlled. There are only 6 special solenoids, (the top jet bumpers, the kickers, and the ramp down coil) So the switches should not be an issue. If both sets of jet bumpers are pulling in, the issue may be a deeper logic issue.

If it is indeed just the special solenoids that are activating, and they are all activating at once, my prime suspect would be SR20. All the +5 volts that hold U49 and U50 inputs high go through that series resistor. If that +5 voltage is not present, or weak, as soon as your flipper coil energizes, all the special solenoids will to.

Lucky for you, I just went through a repair on the special solenoid section of my own Whirlwind machine.

Ok, the upper middle jet bumper is special solenoid #5. The circuits operates around U50 (the NOR gate) For the output to go high (and trigger the coil) both inputs have to be low. So the inputs are pin 2 and 3 of U50. Pin 3 is controlled by the same circuit as the flipper coil. If the flipper coils is engaged, then that input should be low. The other input is controlled by the CPU. The signal originates at U54, and then passes through U45 (a 7407 buffer). From there it goes to pin 2 of the NOR gate at U50 (A 7202).

I learned recently that if any components between the +5v source and the NOR input at pin 2 of U50 are bad, it will cause the signal at the gate to read low, thus triggering the coil. Luckily, there are only SR20, C75, AND ZR8 along the +5v input. With the machine in test mode, the flipper coil should engage, and drop Pin 3 low. You should then measure the voltage at the input of the NOR gate at U50 pin 2. You should get a solid 5 volts. If you are reading something less than that, you know there is an issue with one of the three components along the +5v line.

If the 5v line is ok, I would then check to see if U50 itself is at fault, and then work backwards to U45, and finally U54.

I hope this helps..

...did I call it, or did I call it. *smug*