(Topic ID: 310226)

Tech: GND. SHORT ROW 2 error on Demo Man

By steve-o

2 years ago



Topic Stats

  • 8 posts
  • 4 Pinsiders participating
  • Latest reply 1 year ago by steve-o
  • Topic is favorited by 1 Pinsider

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#1 2 years ago

Self-inflicted error on my Demolition Man machine.
After removing the battery holder on the CPU I accidentally grounded the + and -

If memory serves me correctly, this happened to me about a decade ago while doing the similar task on our IJ pin. To remedy it I had to swap one of the Uxx IC chips. It was a simple repair, but I don't remember which one was damaged.

Note: The CPU is super clean and undamaged from alkaline.

I appreciate any help provided for my Ground Short Row 2 WHT-RED R2 repair.

Thanks

DM GS R2 Error.jpgDM GS R2 Error.jpgCPU DM (resized).jpgCPU DM (resized).jpg
#2 2 years ago

Bump.

I came across this drawing from an old T2 CPU issue here and I am curious if you believe that U18 or U17 is the logical culprit for my specific issue? Or??

Again, TIA for assistance.

87D61210-9D89-4E13-AE21-86FAEC038058.jpeg87D61210-9D89-4E13-AE21-86FAEC038058.jpeg
#3 2 years ago

U20. I've been down this road. That's the one that blew on my JM: https://pinside.com/pinball/forum/topic/jm-all-switches-closed-upon-start-up

EDIT: Zaza upvoted my comment - that's all you need to know. The guy is a god amongst noivce pinball repair guys.

#4 2 years ago
Quoted from NPO:

U20. I've been down this road. That's the one that blew on my JM: https://pinside.com/pinball/forum/topic/jm-all-switches-closed-upon-start-up
EDIT: Zaza upvoted my comment - that's all you need to know. The guy is a god amongst noivce pinball repair guys.

Thank you very much @NPO
U20 does sound a wee bit familiar! I do so appreciate it!
Cheers, Steveo

#5 2 years ago

Just to be sure disconnect your playfield switches from the MPU. I thought I did what you think you did on my Indy 500 last week. But disconnecting the switch connectors from the MPU cleared the row short. I actually had a shorted switch that I only noticed coincidentally after working in the back box

#6 2 years ago

Thanks @the_pump_house
I’ll verify that before I place my order @ GPE tomorrow.
Much appreciated!
Steveo

#7 2 years ago

Your U20 is soldered and likely original.

Unless you have EXCELLENT soldering skills please don't attempt to replace that chip. The PCB tracks on these boards are stupidly thin and the tech for making PCBs back then was not as good as today's boards.

Unless you are VERY good at board work and soldering in general you are bound to cause more problems than you fix trying to change this chip.

Also, make sure a socket if fitted so it's easy to change next time.

3 months later
#8 1 year ago

Put a fork in it.
My DM’s Row 2 Short issue is resolved.

This project went on the back burner for a couple of months due to time. I want to give a huge “thank you” to those that supplied repair info as it was indispensable.

What was done…
New U20 IC and socket.
I pretty much did all of the wrong things while doing this even though I was given great direction. My bad for sure.
I ended up trying to remove the original U20 IC intact and without a desoldering iron. I’ve done this at least twice before many years ago and had zero issue.
.. I had to recreate two traces due to my errors, but all paths tested good afterwards.

I reinstalled the repaired CPU and the Row 2 Short remained.

I had metered many of the involved switches on Row 2 and all (that were tested) were good. I got lazy and didn’t test all….

I pulled the CPU from our good working Judge Dredd and swapped it into our Demo Man and the short was still reported.
The Demo Man’s CPU with my repaired U20 worked flawlessly in JD….

Yep. I made a simple repair stupidly difficult and time consuming.

Back inside Demo Man’s cabinet I quickly (…like within 15 seconds) found that switch 12 (Left Handle Button) was my GND. SHORT ROW2 error.
So simple.

Hopefully, my lesson has been learned and I will check -every- switch in the Row if this ever comes up again….

Steveo

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