post this in the twilight zone club...more ppl will see it...I'd check your active switches and see if one is stuck on...

Your Gumball motor is run by Q32 on the power driver board.

Sometimes these transistors fail, and when they do they turn something on as soon as you turn on the game... like a gumball machine.

Usually a TIP102 transistor will fix this.

Q32 will test as a dead short if you get the board out and test it.

If Q32 doesn't test as shorted, let us know and we'll look at a few other causes.

You did great describing the problem. The key is 'as soon as power is turned on'. That really helps confirm that this is definitely a shorted transistor.

Let us know what you find!

If some switch were the problem I'd suspect that the computer would have to be fully booted so that the software could determine to turn on the motor.

Because this shows up 'as soon as I power up the game', it can't be something that requires the computer to be fully booted to determine which switches are active and make the motor turn... it has to be a the motor getting directly connected to ground.

This is very common when a transistor shorts, and in the manual:

https://www.ipdb.org/files/2684/Bally_1993_Twilight_Zone_Operations_Manual_OCR_searchable.pdf

On PDF page 2 is a chart that says the motor is controlled by Q32.

I'd REALLY expect this transistor to be shorted, and replacing this transistor to solve the problem.

yeah powered up really didn't differentiate if it actually booted, went into attract mode etc, but yes I agree if that's the case sounds like the transistor if it does it as soon as turned on....or some other grounding/wiring issue.

*blinks in astonishment...*

You have an interesting problem!

(You never want your technician to say you have an interesting problem...) *hehe*

Other board technicians might step in here, but I don't know that I've ever had a failure of the U3 74LS374 chip without a failure of the driver or predriver associated with it... (Q32 and Q31, in this case).

*looks doubtfully*

I suppose it's... possible.

I was just reminded that a guy named Ken Layton here would say that an electronic component could fail at any time for any reason, or no reason. That's true.

The plug at J125 is very unlikely to be plugged in to the wrong socket anywhere else, so that's hardly worth checking...

Hmm...

At this point if the power driver board was in the game I'd pull J125, and see if the gumball machine starts running when the board isn't connected.

This would mean that the blue-grey wire on J125 pin 9 is shorted to ground, thus supplying ground all the time to the motor, and you'll have to find the place where it's pinched and shorted to ground.

If the board was out of the game, I'd double down on the stuff in the Q32, Q31 area, check all the components in that section of the circuitry.

The schematics for this are here:

https://www.ipdb.org/files/2684/Williams_WPC_Schematics_Revised_May_17_1993_.pdf

PDF page 7 has what you are looking at.

If all the parts in the predriver/driver transistor area test good like the ones around it, then I'd pull U3 and put in a socket and a new chip.

The problem has to be confined to U3 and down... because problems further up would mess with the data bus for lots of other things in the game.

Good luck, and let us know what you find!

Hey!

Good catch!

It is rare for these 'passive' parts to be the problem without visible indications of failure (obviously broken, looks like it got hot, or completely burnt up...), but it's possible.

I'm just impressed that you replaced U3 and the transistors a couple of times and didn't mess anything else up... that's good soldering skills!

Thanks for letting us know!

A resistor that failed with decreasing resistance...better call Ripley's!