Williams Firepower II (Williams, 1983) Solenoid fuse blowing

[arachnofreak]

We have a firepower 2 machine that has been through hell and back and is working now. We have a full set of new boards from kohout and they are working great( MPU, driver, and power supply). The solenoid circuit keeps popping fuses and we can't figure out why. We tested resistance on all solonoids and they check out ok. During solenoid testing mode for long periods of time it works perfect but during game play it pops the fuse at random times. Sometimes goes for many games but sometimes blows right away.
We did some testing this weekend and changed a few things but the fuse still blew again. We tested the bridge rectifier and it seemed to test ok. We ran the solenoid testing and fired each one for a constant 10-15 minutes and checked the heat with a temp gun. They all seemed to get up to around 78-80 degrees F which to me seemed normal?
We inspected all the wiring for like the fifth time. We changed the out-hole coil just because we suspected an issue as it has been stuck before and it's a different coil then the rest in the machine. So after all the testing we played maybe three games and the fuse popped. We instantly popped the playfield and started looking. One of the pop-bumper solenoids was hotter then the rest and upon further inspection we noticed the plastic piece at the bottom of the coil was cracked in half and could easily move up and down with vibrations pulling on the coil wrap wire. So we immediately changed that coil out. After that we played 4 player games for 2-3 hours and the fuse never blew. Of course we were hoping the problem is solved but no luck. Fired it up Sunday and popped after 3 games.
We are grasping at straws now and it is getting very frustrating.

Anybody have an idea on where to go from here????
Thanks!

 

[faralos]

I would suspect a floating short somewhere
like maybe a coil is bleeding off some electricity?
Check all coils for their proper voltages while on and while off to
make sure that they aren't on all the time possibly heating up the fuse enough to cause it to fry
check all leaf switches too to ensure that they are not touching when they aren't supposed to be
do a solenoid test too to make sure that they open and close properly

 

[pinballdaveh]

if you have a dmm you can use the dc 10 amp range. remove fuse and clip on dmm leads to fuse holder. on most dmm's the positive lead jack will need to be moved to the 10A hole. turn machine on and start playing, check for highest reading on dmm while playing. a minus sign on dmm means that leads are on the fuse clips backwards.compare readings taken to what manuf. says amp size should be.