I picked up a Williams Grand Prix recently which was playing but had a few issues to sort out. I have corrected the following thus far to give you background on my current unsolved issue – bonus count/points.

Issue 1:
Points would not carry over from 1000s to 10,000s or 10,000s to 100,000s for any of the 4 players. After reading many threads, study the schematics and manual and even having tech out – still no solution. I thought it had to be player unit since I saw ”In circuit to 10,000 point relay, thru 9th position switches on 1,000 point drum unit” on page 16-17 of the manual. I noticed quite a bit of Vaseline (or something!) on the contacts of the player unit. I decided to wipe all of that off and clean it with alcohol.

THE SOLUTION – The disc on that unit must have been put back on upside down (it can only go on 2 ways). Once I put it on the other way, problem instantly fixed for all 4 players!

Issue 2:
The “Advanced Left Bonus” and “Advanced Right Bonus” at the top of the playfield would not alternate when the bumpers next to the very top outhole were activated.

THE SOLUTION – minor switch adjustment in the Number Match Unit in the back box.

Issue 3:
The “Scores Bonus” giant red arrows on the playfield would not consistently alternate/light between balls (these indicate which side you collect the bonus on). It should be left for balls 1, 3, 5 and right for balls 2 and 4.

THE SOLUTION – loosen the screw on the PCB on the Ball Count Unit and turn the board about 1/8 an inch so the wipers line up again.

Which bring me to unsolved Issue 4:
If you hit the left or right kick-out holes or the ball drains, you should receive your bonus count based on the arrow that is lit. The playfield indicates 5,000, 10,000 on up to 50,000 for each giant red arrow light on the field. This works, but the I only score 1,000 points (sometimes 2,000 or 3,000) per movement and it just doesn’t sound right compared to the youtube videos I see of normal functions. Sometimes it just rushes through it without awarding points at all. See youtube links below. Both the left and right bonus counts behave this way.

1000 or 2000 bonus count per movement (more common thing that happens) -

Rushing through bonus count - no points (more rare, but it happens) -

Any insight is greatly appreciated!

HowardR! Thank you very much! You called it all day long. It was indeed the exact motor switch you highlighted. When I manually moved the stack I could see it was just never making good contact. Minor adjustment to that switch and everything started pulsing and counting as expected. This fix didn't even take 10 minutes! Thank you again. All that is left now is to mark this one solved, donate and archive. Thanks again.

Indeed it was! To answer your question... I don't know now since everything works now that I adjusted that one switch. Forgot to mention top outhole wasnt scoring and now is... crazy that one switch caused that much chaos.

HA! I couldn't agree more! I already gave the wife the heads-up... "Now that it is fixed, I may need to find another to work on."