(Topic ID: 299776)

Stern Grand Prix not entering playfield

By robm

2 years ago



Topic Stats

  • 5 posts
  • 2 Pinsiders participating
  • Latest reply 2 years ago by robm
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#1 2 years ago

Have a Stern Grand Prix that i stripped down and repaired, and it went OK for a bit, then started getting stuck in the outer racetrack (ie: would never enter the playfield).

Now its constantly doing it. Launch the ball, and it just keeps going around the outer racetrack. I am thinking there needs to be certain conditions met for it to open the right diverter to allow the ball to enter the playfield, adn wonder if its something to do with timing of optos OR if there is a switch issue.

What i have done:
* Tested many many times the track test - all optos work 100% of the time, and i've watched the ball go around and around for minutes in the test with no optos missing (3 lower and 2 upper sets of optos)
* Tested the launch switch - works 100% of the time

What i find strange, is that if i start a game, and the ball keeps lapping around, and manually place it on the playfield, some of the coils do not fire (slings). Flippers and pop bumpers work fine. Its not until i hit the car mech, that the other coils start working.....

Another potential clue, is that the machine does come up with a tech error to check sw 39 which is car mech down. Now i have checked and double checked this switch, and it works 100% in the switch test (using the mech, not my finger), as well as 100% of the time in the car mech specific test - yet the machine keeps saying to check it in the tech alerts section of the menu - anyone have any idea at all why this would occur?

I even tried disabling the track, yet not sure how this is meant to work, as it still wouldn't enter the main playfield

I notice in the Grand Prix specific adjustments, there are to menus for 'Track Adjust' but the manual says "For factory service use only" so no idea if this can change the timing of anything to get the game to correct itself?

#2 2 years ago

Ive'also noticed the wheel inside the truck spins slowly, and its not until i manually put balls in the playfield during a game and hit the car mech and other switches that it starts spinning faster (at normal speed). So it seems to me the power going to a group of coils (wheel motor, diverters, slings) is low or off until a certain set of conditions are met...no idea what those are though!

#3 2 years ago

I pulled the power driver board out and did notice some pins had some marginal cold solder joints, so reflowed them. Also put in a different ribbon cable, and noticed that the uppper of the 3 lock switches on left side was a little sticky, so cleaned and adjusted it.

With all of those 3 things, it appears to be working OK for the moment - not sure if it was a combination of issues or just one.

#4 2 years ago

The optos used for Whitestar games are known to degrade faster than most all other optos used in pinball. They become prone to phantom closures from flashers. If they look original, replace all the launch optos. Not suggesting that was your original issue, but I'd still recommend it. Seen enough flaky old optos on Whitestar games.

#5 2 years ago

Hmmm. So left the machine off for a few hours, then started a game. It did about 8 laps, then finally let the ball in. What was interesting is that i could see the right diverter gate flutter/partially open a few millimetres after the 3rd or 4th lap. Its like the power for that diverter needs time to warm up to get there.....

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