I've a pinball machine that keeps blowing the transistor for the flipper coil. The flipper coil has a diode across the lugs. This tested good but I replaced it with a new one anyway. Still blows transistor. I've buzzed out the lines from all three legs of the transistor and I am not finding any shorts and signals go to where they should. I know its not in the coil as I've connected the side that is not blowing to the one that is blowing and the flipper works fine like this. I feel the issue is somewhere on the board because I have blown the transistor with the the coil out of circuit. The line going to the gate does have a filtering cap between the gate leg and the resistor coming from the signal. Could this cap be causing a ground short if it is failing and cause the transistor to short? The transistor in question is Q15 and has been replaced with an IRL540N due to having a higher amp capabilities than the original. Cap in question is C248 and is 0.01uF. C256 is a blank pad. There is no cap on the board here.

enter image description here flipper coils and switches path

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    \$\begingroup\$ You really cannot overdrive the GATE of a MOSFET with excess current since they present a very high impedance to the driver. You can, however, overdrive voltage and breakdown the GATE insulator and kill the device. I'd check that the circuit driving the GATE is not exceeding the rated input limits. \$\endgroup\$ – jwh20 Jan 13 at 14:05
  • \$\begingroup\$ The max threshold voltage for the IRF540 is 4V compared to 2.5V for the STP20N10 so it may be that it's not turning on fully and overheating. \$\endgroup\$ – Finbarr Jan 13 at 15:40
  • \$\begingroup\$ Finbarr I appreciate your response. I'm using an IRL540N and the max threshold is 2V. The reason for using the IRL540 over the STP20N10L as a replacement is the IRL540 has a higher amperage rating and stand the use better. There has been discussion on using the IRF540 but the consensus is it will not work because of the higher voltage needed to operate the gate. I will check the voltage driving the gate and see what I get. \$\endgroup\$ – maestro Jan 13 at 23:04
  • \$\begingroup\$ I checked the voltages. Flipper side that is working voltages are 0.458 between U2 and resistor and 0.457 after the resistor. Flipper side that is blowing the transistor is 0.440 between U2 and resistor and 0.439 after the resistor. \$\endgroup\$ – maestro Jan 14 at 17:49
  • \$\begingroup\$ Replaced and socketed U2. Issue resolved. \$\endgroup\$ – maestro Jan 19 at 17:28

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