Transistor on 6A sparking or grounding...

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sc2dave
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Transistor on 6A sparking or grounding...

Post by sc2dave » Tue Jan 16, 2018 10:39 pm

I have this transistor ,https://www.ebay.com/itm/Motorola-2N588 ... 0827746372, that is either sparking to ground, or something else is grounding to it intermittently. The MSD 6A has 2 of these. 1 of them is cold to the touch and the 1 that is grounding is pretty warm. This happens when the box is in use. It has a different screw that holds it down, than what came with the box. Should it run warm? This was after only a few minutes of idle.

Zmechanic
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Re: Transistor on 6A sparking or grounding...

Post by Zmechanic » Tue Jan 16, 2018 11:25 pm

On those transistors, the metal case serves as one of the connection leads. There is likely to be an insulator under it and around the mounting screws. If either of those is damaged it could be intermittently shorting to the case.

Warm is not as alarming as it is probably dissipating some decent power in operation.

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Re: Transistor on 6A sparking or grounding...

Post by JohnP » Wed Jan 17, 2018 12:42 am

According to page 15 of the 6A schematic posted online, those transistors are in parallel. They should share the load and be of equal temperature.

http://web.tiscalinet.it/giordy/ECU/msd6a_02.pdf

The case of each should be bolted to ground. I suspect the one that is arcing is not grounded.
Thinking is hard work.

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Re: Transistor on 6A sparking or grounding...

Post by joe 90 » Wed Jan 17, 2018 12:50 am

It's a bipolar transistor rated at 80v and 25A.

Do a diode test between BC, BE and CE on both of them. That's to look for a short. It's probably the cold one.
That means taking them out.
Either that or replace both of them.

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Re: Transistor on 6A sparking or grounding...

Post by emsvitil » Wed Jan 17, 2018 3:15 am

If you're replacing them, replace them both.

If one failed (for whatever reason) the second could be on the verge of failing.
Ed

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Re: Transistor on 6A sparking or grounding...

Post by Circlotron » Wed Jan 17, 2018 6:46 am

Sounds like one of them is not screwed down to the metal box properly and so the other one has to do all the work and so is getting warm. They do not have an insulating washer underneath them, they make a direct connection to the earthed box. The sparks could be coming from the intermittent connection. If one or both are shorted it will blow a small fusible link on the board.

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