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(Topic ID: 267904)

+5v and GND test as continuous - Sorcerer Sytem 9 MPU

By BC_Gambit

5 months ago

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  • 7 posts
  • 3 Pinsiders participating
  • Latest reply 5 months ago by BC_Gambit
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#1 5 months ago

I am working on an acid damaged MPU and just as I thought I was almost done, I was doing some continuity tests and found that the +5V and ground "shorted out" (tested as continous) with my meter.

Setting to Ohms I think I get ~17 ohms between them.

This goes over most of the board (e.g. all of the "bypass" capacitors test as "continous" when testing both sides, and both sides of these capacitors test as continuous to ground.

I have spent even more time checking my work, but as this MPU's functionality is unknown I don't know if there is a problem hidden somewhere (blown chip?) or if this is just normal and it would work if I was blissfully unaware and plugged it in.

Hopefully someone knows this off the top of their head.

Otherwise, can someone please test the continuity between PINs 1J17 on the MPU board for their system 9 game? Pins 1-3 should test to ground. Pins 4-6 should be all +5v. On my MPU they all buzz as if they are connected to each other with a 17 ohm resistance.

Thank you in advance for any help with this! This drove me crazy yesterday; and I sorta gave up. Now I am at the "maybe it IS normal" phase... that could be "denial" kicking in

full board (resized).PNGschematic pic (resized).PNG
#2 5 months ago

Bump for the morning crowd!

Also cross posting with the sorcerer thread.

#3 5 months ago

good visual inspection goes a long way.

resistance / voltage should measure lower the closer you get to the short.

slice and dice the 5v rail into sections to try and isolate what section the short is in.

#4 5 months ago

Thank you for the reply. Still hoping someone can test me just to confirm the error before driving in more. I will have a look at the video after work ends tonight. I may go full crazy and get a bench power supply to test the board out of the game but I am just trying to take a step back first.

#5 5 months ago

I watched the vid. I wonder what voltage that battery was?

I did not know Randy fromm had a YouTube channel. That brought back memories of my brief coin op career 2 decades ago..

#6 5 months ago

Not normal.
Somewhere, you have some kind of solder bridge (not that likely as resistance would be near zero) or you have a failed part.
You can start "diode testing" the parts on the board, using the schematics as a guide to see what is tied to ground and what is not.
I've done this many times, usually trying to track down blown chips after the body-to-head harnesses were swapped.
Chris Hibler - CARGPB #31 - The Place to go for Pinball Repair Info

#7 5 months ago

Thank you for making the time to confirm I may be screwed for now Chris! I appreciate not spinning my wheels further on this board. I will look into the diode testing method and see if I can eventually find the source of the issue.

I ordered a replacement board tonight as I was going to get one anyways as a backup. But at least I know that the older board has some more problems to work through.

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