(Topic ID: 179367)

Transistor differences, Stern T3


By cmndr-brain

3 years ago



Topic Stats

  • 6 posts
  • 5 Pinsiders participating
  • Latest reply 3 years ago by RVApinballer
  • Topic is favorited by 1 Pinsider

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#1 3 years ago

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?

#2 3 years ago

If you dont cut the leads short enough after soldering, I have seen the transistor ark and short out to the metal plate behind the board

#3 3 years ago

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?

#4 3 years ago
Quoted from cmndr-brain:

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?

The manual is a guide only. Manufacturers change specifications and all sorts of things all the time. Sometimes the changes are made after the manual has been prepared.

You coil might draw 14A but for a very short time. The power supply could not supply 14A other than for a split second supplied from the filter caps.

I wouldn't overthink the problem. Replace the MOSFET with an IRL540 - make sure none of the wires are trapped anywhere and that the connectors are all sound.

#5 3 years ago

Also change the diode on the coil, it could be shorted. Pay attention to the orientation of the diode.

#6 3 years ago

I'm pretty certain what you need is the IRL540N. Pay attention to the L part of that, and make sure you don't buy the F

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