SOLVED: Doctor Who MPU issue causing multiple Switch grounding?

Hey guys,
I've been having this issue with my DW for a while but am now just getting around to working on it.
Every switch of Column 4 grounds out in TEST mode and I've traced it back to my MPU. I swapped out a known working MPU and the issue goes away. I've tested from J206 pin 4 to C14 & R70. Both C14 & R70 test differently from all the other capacitors & resistors in their rows on my DMM in diode test. So I assume that's part of the issue... I was hoping someone has some insight on this type of issue...what might cause it and if I should worry about U20 as well.

Thanks
ERIC

Post last edited 2 years ago.

#2 2 years ago

KJO

eyeamred2u

Pinside+ Frequent

OP
Quoted from qbass187:
Hey guys,
I've been having this issue with my DW for a while but am now just getting around to working on it.
Every switch of Column 4 grounds out in TEST mode and I've traced it back to my MPU. I swapped out a known working MPU and the issue goes away. I've tested from J206 pin 4 to C14 & R70. Both C14 & R70 test differently from all the other capacitors & resistors in their rows on my DMM in diode test. So I assume that's part of the issue... I was hoping someone has some insight on this type of issue...what might cause it and if I should worry about U20 as well.
Thanks
ERIC

Look at the following diagram, and yes, consider U20 could be blown.

WPC-089MPULayout (resized).jpg

#3 2 years ago

EPB

qbass187

Thanks man!!! I’ll post what I find.
This diagram is amazing. Did you make it ?

Quoted from eyeamred2u:
Look at the following diagram, and yes, consider U20 could be blown.
[quoted image]

#4 2 years ago

???

Robotworkshop

Pinside+ Frequent

7y 80,800 3,378

Is there any battery corrosion on the board that may have leaked down into U20 and the connector for the switches?

#5 2 years ago

EPB

qbass187

None visible.

Quoted from Robotworkshop:Is there any battery corrosion on the board that may have leaked down into U20 and the connector for the switches?

#6 2 years ago

TOX

ChrisHibler

Chris' Pinball Repair

Chesterfield, MO

12y 120K 9,996 46

That diagram came from the PinWiki. It was meticulously created by Sascha Voskuil
See: https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Switch_Matrix_Problems

Are you saying that every switch in column 4, when pressed, creates a "ground short row n"?

The traces on that board are delicate. I'd advise sending it to a pro. He/she can add NVRAM to the board while it is there.
I can take care of it if you wish. Happy to help.
--
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/Contact ... for board repairs
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#7 2 years ago

KJO

eyeamred2u

Pinside+ Frequent

OP
Quoted from qbass187:
Thanks man!!! I’ll post what I find.
This diagram is amazing. Did you make it ?

No, can't take credit for someone else's fine work.

#8 2 years ago

KJO

eyeamred2u

Pinside+ Frequent

Quoted from ChrisHibler:
That diagram came from the PinWiki. It was meticulously created by Sascha Voskuil
See: https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Switch_Matrix_Problems
Are you saying that every switch in column 4, when pressed, creates a "ground short row n"?
The traces on that board are delicate. I'd advise sending it to a pro. He/she can add NVRAM to the board while it is there.
I can take care of it if you wish. Happy to help.
--
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/Contact ... for board repairs
http://www.PinWiki.com - The Place to go for Pinball Repair Info

Thanks Chris, My mind drew a blank on the name, but I am glad you chimed in.

#9 2 years ago

CDG

Tophervette

Pinside+ Frequent

3y 84,050 1,588 1

I have also learned from this post. Thanks. I even printed the picture of the board for future reference. I have also copied Chris Hiblers info for future board work. This site is amazing...

#10 2 years ago

EPB

qbass187

Yes, that’s what happens. Every switch in the column shows ground short.
I ordered the parts to replace to resistor/capacitor & U20 and if that doesn’t do the trick I’ll definitely send it you way!! I appreciate the heads up!!

Quoted from ChrisHibler:
That diagram came from the PinWiki. It was meticulously created by Sascha Voskuil
See: https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Switch_Matrix_Problems
Are you saying that every switch in column 4, when pressed, creates a "ground short row n"?
The traces on that board are delicate. I'd advise sending it to a pro. He/she can add NVRAM to the board while it is there.
I can take care of it if you wish. Happy to help.
--
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/Contact ... for board repairs
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#11 2 years ago

TOM

pinballinreno

Computer Extreme

9y 134K 15,516 31

OP
Quoted from qbass187:
Yes, that’s what happens. Every switch in the column shows ground short.
I ordered the parts to replace to resistor/capacitor & U20 and if that doesn’t do the trick I’ll definitely send it you way!! I appreciate the heads up!!

Send your CPU board and driver board to Chris Hibler.

He will bullet proof them and they will be like new.

He is excellent in his work.

Its what i did and my boards were trashed. Really trashed, most people would throw them away.

They look like brand new boards now.

I was quite impressed and wont go anywhere else.

The work he did on my DW and Funhouse was incredible.

Get some trifurcons from ed at GPE and redo connectors until the game is rock solid. Especially the GI and light board insert connectors.

#12 2 years ago

EPB

qbass187

UPDATE: I replaced U20, R70 &
C14 and the problem has been resolved.
I’m still not clear as to what caused this is the first place but as of now it has been resolved. Thanks to everyone for their help & advice.

#13 2 years ago

KJO

eyeamred2u

Pinside+ Frequent