(Topic ID: 200799)

1978 Williams World Cup System 3 power supply board short

By BingHawk

4 years ago

Topic Stats

  • 7 posts
  • 3 Pinsiders participating
  • Latest reply 4 years ago by Grizlyrig
  • No one calls this topic a favorite


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#1 4 years ago

Hello Everyone!,
I am a newbie to home pinball repair, but I am handy and have an ohms meter so going to give it a shot.
As the title says I have a 1978 Williams World Cup that uses System 3. Based on my research so far it looks like it has all the original parts, so no board upgrades or anything.

It was last switched on about 25 to 30 years ago, at that time it made a pop noise and then basically stopped working.
The current state of the machine, when you turn it on, the back glass lights and play field lights come on.

I opened up the machine and noticed the F2 fuse is blown (it's a 2.5amp slowblow) along with damage to the circuit pathway.
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Tracing the path I found severe damage to connector 3J2 on the board (3P2 listed on the power supply board connectors?).
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I don't think I am going to have the board rebuilt. I can buy a replacement for about $100.
BUT I don't want to drop it in without fixing the problem that caused it in the first place. I am a little lost on where to start troubleshooting.
I have the original manual and circuit diagrams that came with the machine. I am not familiar with how to read them very well, so I am hoping someone here can give me a few pointers on where to start troubleshooting. I have attached what I think are the relevant pages from the manual and diagrams.
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Any thoughts or guidance based on experience with these machines would be appreciated.


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#2 4 years ago

Looking at the damage I would think to test the bridge rectifier for solenoids as the F2 fuse is for the solenoids. Look for any charbroiled coils that could have locked on.That would be a dead give away as to what happened.

#3 4 years ago

Thanks for the help!
here is an update:

I tested both bridge rectifiers and they seem to check out ok.
I looked over all the coils on the play field and nothing seemed obviously burnt out. However during my testing I found something "interesting".
If I read the diagrams from the previous post correctly, then Pin 3 should go to the Solenoid Rectifier and Pin 6 should be going to the Lamp Rectifier.
but this doesnt appear to be how its currently connected.....

It's hard to see in the image below but the black wire on the left of the molex connector is Pin 3, and it connects directly to the rectifier on the right which is the Lamp rectifier.
The wire going into Pin 6 connects to the giant capacitor and then connects to the Rectifier on the left which is the Solenoid Rectifier.

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My questions are
1- Am I understanding the wiring diagram correctly?
2- Am I understanding how the the current wiring is currently connected correctly?
3 - Does it matter? (assuming it does I may have just found my problem)

Thanks again

#4 4 years ago

The pin 3 / 6 swap doesn't matter for this board. They both tie to ground on the power supply.

What Williams *should* have done is tie solenoid ground to both pins 2 AND 3 using paralleled wires.
And they should have also tied lamp ground to both pins 5 AND 6 using paralleled wires.
This would have helped J2 to be a bit more reliable but J1 would still be a PITA.

Now ... if the one going the the lamp circuit is the one that shorted, check for shorted lamp sockets/wiring.
Maybe too large of fuse?

#5 4 years ago

I also see a 1979 date code on the main filter electrolytic cap in that photo. Time for a refresh for those nearly 40 year old caps.
Rather than replace the power supply with a less reliable supply (imho) - wouldn't take much to get that one back into shape.

#6 4 years ago

Thanks again!
I am not too familiar with diagnosing circuit boards and have no experience working on them. I was trying to be realistic about my skill set. I thought the pathway damage near the F2 fuse was a deal breaker for any board refurbish or repair.
But if you think its salvageable and have a recommendation on where I can get it rebuilt I would gladly take it .

Status Update!
I think I may have found the source! I was looking under the play field for anything obvious and came across this shattered bulb under the right ball kicker.
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I played with the kicker a bit and noticed that it had enough movement to come up and impact the bulb.
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I think it's a good guess that the kicker came up, broke the bulb, and created a short.

I then took a look at the fuse holder under the play field...... The one clearly labeled "10 AMP Fuse" in bright read letters....
It had a 15 AMP fuse in it (facepalm).
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At this point I think my next steps are to:
Replace/repair/refurbish the power supply board.
Replace the fuse under the play field with a proper 10 amp.
Adjust the kicker so it no longer hits the bulb.
Replace the bulb.

#7 4 years ago

Glad you found it. Take a look at Vid1900 showing us how to bulletproof the Williams machine- it's very good topic.
Hope this helps.

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