(Topic ID: 46684)

Please help a newbie with an oldie... Williams Grand Prix

By Dickydo

6 years ago

Topic Stats

  • 12 posts
  • 10 Pinsiders participating
  • Latest reply 6 years ago by Rody
  • No one calls this topic a favorite


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#1 6 years ago

Hello, folks, and new to this forum. I have a Williams Grand Prix electromechanical pinball machine. Owned about 15 years, was working fine. Forgive me, I don't know a lot about electronics, but am very mechanical.

After not being used for a couple of months, a problem has developed. There are three holes in the play board where the ball drops in, points add up, and then the ball is kicked out of the holes and back into the field of play. When the ball drops into any of the three holes, or in the drain below the flippers, I hear a continuous "ker-chunk, ker-chunk, ker-chunk," but the ball does not get ejected.

Can someone please provide a suggestion as to how I might fix this? I do have the factory manual for the machine, but I'm kind of overwhelmed when I open up the lid and stare hopelessly at the 36,874 sets of points, relays, and other electrical bits.

If someone can get me in the right direction, I'm certainly capable of filing/sanding points clean, using electrical spray cleaner, etc.

Thanks in advance for any guidance you might provide.


#2 6 years ago

Sorry I can't help with your problem - but WELCOME to Pinside. There are some great EM folks here who I'm sure will chime in eventually.

#3 6 years ago

For a start, look over what kicks the balls up. Could be as simple as a good cleaning of the pivots points and a drop of fresh oil.

LTG : )

#4 6 years ago

Sounds like your score motor is running, but a switch must have build-up on it and not engaging. That happens when they sit. EMs are tough to figure out (at least for me) without seeing it in person. You will have to see what relays are engaging when it happens which means lifting the pf. If you do this - be very careful with high voltage present in certain places. Best to try to find someone local to help out

#5 6 years ago
Quoted from Dickydo:

... using electrical spray cleaner ...

you won't need that talent... that's a big no-no on an em...

as alluded to in the couple other posts, the issue is likely not with the part making the "kerchunk" noise... it's a dirty switch and/or a gummed up "something or other"... i'm a rookie, but starting with whatever advice lloyd gives is never a bad thing...

do you have a schematic? that would likely help...

2 weeks later
#6 6 years ago

Still looking for help -- please...

I do have a schematic, and I am trainable...



#7 6 years ago
Quoted from Dickydo:

Still looking for help -- please...
I do have a schematic, and I am trainable...

Send a PM off to Chris Hibler here on the board. He will point you in the right direction.

#8 6 years ago

Would a moderator please move this to the EM section.

#9 6 years ago

Where is the ker-chunck coming from? Are you getting the scores when the ball goes in the hole? Can you lift the playfield and activate one of the holes and look to see where the ker-chunck is coming from?

And ccotenj is correct in that you never want to use electrical spray on it. It is very flammable and with all the sparks under the playfield it could easily start a fire.

#10 6 years ago

It's not likely all the switches in the holes have the same problem, but for starts I would check and clean each switch to see if clean and properly adjusted...POWER OFF!

First check the switch stack screws to see if they are tight, if loose tighten the one closest to the blades. Then you can adjust if needed. Those Bakelite spacers between the blades can swell and shrink due to temp.

It may be the score motor switch that is responsible for the power to the kick out holes...could be dirty or not adjusted properly. You would need the schematic for that to find out which one, or sometimes the motor chart is still inside the cabinet.

Hopefully others will chime in and maybe somebody w/the exact fix. Good luck.

#11 6 years ago

Here is some good information on repairing EM's that might help you out.


#12 6 years ago


All three of the saucers activate the bonus unit; the top saucer advances the bonus and the two side saucers count them down.

If the bonus unit is being activated but is not then sending the signal to kick the ball, one of the switches needs adjusting to insure that it is tight and closing.

With the game on, glass off, and the coin door open, drop a ball into a saucer and then look under the playfield. You should see the score motor running and making your "kerchunk".

Your schematics should help you trace the path from the saucers to the bonus unit and then score motor. Tighten all switch stacks, lightly run some emory cloth between the swithes and adjust as necessary.

Good luck!

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