(Topic ID: 93915)

Bad Ground in the switch matrix on JP

By LilRocky

9 years ago



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  • 3 posts
  • 2 Pinsiders participating
  • Latest reply 9 years ago by LilRocky
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#1 9 years ago

I'm working on a JP which has a bad ground off of CN8-1. This is the first time I've had to fix a grounded matrix on a DE, so I'm hesitant on what I need to replace. From doing this on Williams boards in the past, I'm assuming I need to replace the chip I've circled in red on this picture, however, I'm curious if it's Q55 that might be at fault or, hopefully not, the much larger component above the chip I circled in red.

The one thing I do know is that the problem is coming from the board as I've jumped CN8-1 to any pins off CN10 and the switch diagnostic shoots back with a number of different switch activations. Whereas any other combination not involving CN8-1 will result in the normal one switch activation response from the diagnostic.

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#2 9 years ago

You want to figure out what has failed, as opposed to just replacing things hoping you find the culprit, right?

Do you have a logic probe? A DMM?

The best way to figure it out, IMO, would be to check everything along the line from the PIA through the resistor array through the 244 IC to the transistor.

You can figure out the pinouts of the PIA and the 244 IC and compare to adjacent row/columns for proper behavior.

#3 9 years ago

Good call. I'm so used to just assuming it's an issue with a certain part from frequently seeing the same problem, that I totally neglected to simply check. Turned out it was just a bad transistor at Q55, which is definitely the best case scenario as I hate replacing those damn chips.

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