(Topic ID: 169429)

Williams System 7: Switch Matrix issue (SOLVED)

By mof

2 years ago

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


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201609-idiots-will-solder-any-wire-anywhere-they-choose (resized).jpg
switch-matrix-cosmic-gunfight (resized).jpg

#1 2 years ago

SOLVED. Crazy wiring hacks found (of course).

Goal: I’m trying to get a William 1982 system 7 Cosmic Gunfight up and running. The switch matrix has 4 errors remaining in it. I’m starting to troubleshoot switches 9 and 10.

I have two playfields. I’ll call them the “good” and “bad” playfield.

Symptom: When I plug in the good playfield, switches 9 and 10 work fine. When I plug in the bad playfield, switches 9 and 10 report 17 an 18 respectively. Also note that 17 is "not used", and 18 works as expected on its own. Also note that 14 and 16 are reversed, but I'm not troubleshooting that yet.

Conclusion: If a good board works, then the problem is likely in the bad playfield.

Isolation-1: I've buzzed out the switch to the end of the molex, and that seems to work fine for both physical switches 9 and 10 to the corresponding pins on the molex. I haven't checked for a short between various components yet.

Isolation-2: However, when I pull 2J2 off the MPU and check for continuity from the switch to the end of 2J2, I'm NOT good with 9 or 10. This suggests to me that the molex pins for 9 and 10 (red/white and brown/white). When I do this with the good playfield attached, of course I get good continuity. (There's a small chance I'm just not holding the probe in the right place, but I doubt that this would happen to both wires.

Inspection-1: Both 3x5 sets of molex wires look equivalent in both playfields
Inspection-2: Both switch 9's and 10's seem to be wired up the same way

Looking forward to learning how to better track down a short or hack in the wiring.

I'll attach the switch matrix in the next post...

thanks for all help!

#2 2 years ago

Note: this is an early pic. I've since fixed everything that is NOT in 2J2-8.

switch-matrix-cosmic-gunfight (resized).jpg

#3 2 years ago

I repinned white red and white Brown in the male molex leaving the pf in the 3x5 connector. No change.


#4 2 years ago

The wires are daisy chained from switch to switch. Doesn't necessarily start at the first switch in the column and go to the next.

Check continuity on the green-red wire from a working switch to a non-working switch. I bet you've got a wire break somewhere. Look around the working and non-working switches to see if any wires are hanging. Tug gently on the wires and see if any break off a switch that may have already been internally fractured.

#5 2 years ago


And tug on your diodes. They often break between your fingers when bad.

#6 2 years ago

Really? Someone attached a wire from the pop switch to the rollover switch?

201609-idiots-will-solder-any-wire-anywhere-they-choose (resized).jpg

INSTEAD -- the switch on our right should reach farther right and daisy chain power to the next rollover over (1-2-3)

Never assume the wiring is correct !!! Haven't seen that since Sorcerer 3 years ago...

#7 2 years ago

As for 14 and 16 -- they were WIRED backwards. Lovely!

#8 2 years ago

Thanks for the help.

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