Arcade Collecting > Pinball
System 11 Stuck Coil, Please help.
smartbomb2084:
Had a similar problem on an EARTHSHAKER and U49 was fried alongh with U50.
I'll bet pin 12 of U49 is shorted (output F)
Santoro:
U49 did not do the trick. Investigating shorts now.
I have found that BOTH sides of the pop bumper trigger leaf are grounded even when the machine is off. None of the working bumper switches are like that. Could this be caused by a bad diode or capaciter on the switch?
Santoro:
--- Quote from: lilshawn on July 24, 2010, 07:49:41 pm ---you can check by disconnecting the offending solenoids return wire from the board. what this will do is isolate the power wire and the coil and it's return... if it is indeed shorted someplace along the return the solenoid will still come on.
--- End quote ---
So I did this. The coil is not locked down when the return is diconnected from the CPU board. If I short it to ground it fires. This means i do not have a short the way I understand it.
--- Quote ---if it does not, perhaps you have replaced the wrong transistor... i've done it before.
--- End quote ---
I have quadruple-checked this, it's the right one. I am certain this is related to the switch problem I found. Thinking back to how this happened, if I shorted the leaf switch somehow could that have fed back and caused a pernanent short somewhere unusual on the CPU board switch circuitry? I need to pore over the schematics to see where the switch wire goes to on the CPU board and check components there. Leave it to me to have a stuck bumper that is different from 99% of the other causes out there. ::)
Santoro:
I was right, found a bad diode right where the bumper switch comes into the CPU board. The diode is permantly closed to ground. Off to fix that.
Santoro:
Still no good after replacing the diode. The only thing left to replace in this circuit is the SR20 resistor network, and I just found out that the section of that connected to this circuit is hosed too. When I shorted this thing out last year I must have horked every component along the way.
I need to order a resistor network, so I am done for a few days. Thanks for all the help.
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