TECH: Coil only fires when grounded

robgest

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When going through the tests on my pin I can't get the coil to fire, unless I ground the transistor. I replaced transistor, cap, and coil/diode but still not getting it to work (only humm) I just tried again and if I hold the shaft half way down the coil it will pull it down. It acts like it just doesn't have the power it needs except when I ground it straight from the transistor. BTW it a 6803 board.
 
When going through the tests on my pin I can't get the coil to fire, unless I ground the transistor. I replaced transistor, cap, and coil/diode but still not getting it to work (only humm) I just tried again and if I hold the shaft half way down the coil it will pull it down. It acts like it just doesn't have the power it needs except when I ground it straight from the transistor. BTW it a 6803 board.

I would check the pre-driver transistor. On those games there's also a diode in series between the pre-driver and driver. Check that too. Almost seems like the driver transistor is barely being biased due to some funkiness in the pre-driver circuit.

EDIT: Assuming that it's working just fine when grounded at the driver transistor tab and the driver transistor is new. Also assuming that all of the other coils are working normally. You may also have a bad new transistor but that seems less likely.
 
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