(Topic ID: 215166)

Troubleshooting DESW Switch column

By Ollulanus

4 years ago

Topic Stats

  • 5 posts
  • 3 Pinsiders participating
  • Latest reply 2 years ago by Sirgubster9
  • Topic is favorited by 1 Pinsider


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#1 4 years ago

Ok, first pinball, first board problem, teaching myself circuit diagnostics from scratch, so bear with me

I have a full column failure in the switch matrix of my DE Star Wars, specifically the one driving the slings, pops, and the death star gate. I have verified continuity from the board to playfield wiring on the column with my DMM, and power is not the issue as the pops/slings will fire in diagnostics mode. I'm 99% sure it is a problem on the board.

Hooked up the logic probe. Each drive circuit runs through a resistor into the NPN transistor and out to the board. All the wires into the resistors are pulsing, so I'm taking that to mean everything is good upstream. The bad column is reading high at the wire out of the resistor, and the drive column resistors all read low. This makes intuitive sense to me - bad resistor, replace and move on?

Thanks for reading, new to this and just want to make sure I'm understanding things correctly!

#2 4 years ago
Quoted from Ollulanus:

bad resistor, replace and move on?

I'd do that and then see where you are at.

LTG : )

#3 4 years ago

Replaced the resistor, column is down

Checked voltage with the DMM in the circuit....it's higher than the others going into the resistor (about .5 volts on the good columns, .75 on this one). The really strange thing is that the downstream end of the resistor is running WAY high...about 3.5V. doesn't make sense to me why I'd read HIGHER voltage past the resistor...

Is there any way a bad transistor could mess with the voltage UPSTREAM from it? Or, should I just focus on the slightly high voltage going into the resistor and presume that the problem is upstream? There's a buffer chip between the logic chip and the resistor, not sure how to test that though. There is also a capacitor downstream from the transistor - any way that could be an issue?

I'll probably try swapping the transistor since I have some, but I'm very interestedim getting a better understanding of what I'm seeing if anyone can help...

2 months later
#4 3 years ago

Just FYI, it was the transistor. Replaced and worked like a charm. After looking back at the circuit diagram it made more sense.

1 year later
#5 2 years ago

i know this post is older, but I just PMed you in case you dont look at this anymore.

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