I'm helping a friend fix his Stern Terminator 3. The RPG coil burned up and the transistor has blown. This is at least the second time that I know of. The manual specifies the transistor to be a STP20N10L and that is what it was replaced with and blew up a second time. All the other coil transistors on the board are P22NE1. Looking at the specs, there doesn't seem to be much of a difference other than the P22NE1 can handle 22amps vs 20amps. By my calculations, the coil should only draw just under 14amps maximum, so the lower rated transistor is still well above the maximum. Is there something I'm missing? Which one should I put in? Why did Stern use different transistors than what they say in the manual? Is there a mod to keep this from happening again? Maybe a 15amp SB fuse inline with the RPG coil?

Thank you for the suggestion but, I'm pretty sure the problem is not shorting out to the grounding plane. The legs were cut short enough and there are no scorch marks. Though my question still remains about why Stern used different transistors that what the manual specifies and what should it be replaced with?