(Topic ID: 260801)

Locked Coils on Road Kings


By scupbucket

6 months ago



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  • 2 posts
  • 2 Pinsiders participating
  • Latest reply 6 months ago by pinmike
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#1 6 months ago

Hey guys! I’m working on a Road Kings at the moment and having a tough time chasing down problems with with coils locking on. I originally started off trying to fix a dead left pop bumper by replacing the driver transistor (tested bad using DVM - IJ19 disconnected) at Q69 on the board. After changing out the transistor, I’ve been running into problems with the special solenoids locking on. I should mention that there's zero corrosion or hacks on the board.

I’ve swapped out all the old SS components on the CPU board with new ones. I changed the pre-drivers, drivers (replaced with TIP102), and the 7402 at U45. I’ve also replaced all the diodes on the corresponding coils and double checked their band positions. When the game is powered on all is fine in attract mode. When a game is started, gameplay is normal for about 5-10 seconds and then a coil locks on and cooks the driver. When the game is shut off and turned back on, the coil with the cooked driver locks on immediately in attract mode. So far I’ve had the left bumper (Q69), right kicker (Q71), and top bumper (Q73) lock on all on separate occasions. Kind of stumped at this point and trying to avoid shotgun replacing anymore parts. As always, any guidance where to start troubleshooting is greatly appreciated.

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#2 6 months ago

Ok so 3 coils locking on
Steps to take
1.check the wiring on those coils and make sure they are on those coils correctly.
2.Test diodes on those coils remember you have to remove one leg of the diode to get a proper reading.
3.Check the ohms for each coil with a meter.Must be 2 ohms or higher.
4.Test the transistors for those coils on the board.

Things to always remember when dealing with locked on coils is the coil hardly ever goes bad unless it’s really fried/burnt.
Replace diodes on coils
Replace transistors to those coils on the driver board.
Replace fuses
If you just replace transistor and the diodes are bad on those coils it will just blow out the new transistor you put in

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