ECM Motor Thermistor Help

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Old 11-14-15, 06:58 AM
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ECM Motor Thermistor Help

Got a 1HP GE ECM controlled motor that quit on our furnace. Doing some reading on here and taking mine apart it is obvious that the thermistor (sg379) has blown. My question is what is the best way to replace it and install the new one without damage to the board. I tried pushing one of the "legs" of the thermistor down through the hole and it started to peel the board off the back side. I quit at that moment. Should a guy drill 2 new small holes for the new thermistor and solder them in that way. Or pick at the old one until it is loose and pull it through. All help is appreciated.
 
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Old 11-14-15, 07:36 AM
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In general you would first unsolder the old component and then solder in the new. You need to use a small soldering pencil, not a gun. You can use a solder sucker or desoldering wick to remove the old solder, and then remove the old part. Solder in the new part making sure to use electrical solder.

If you don't have a solder sucker or desoldering wick, you can try heating one lead at a time and pulling out the old part, and then heating one side and inserting the new part one lead at a time. Doing this risk lifting the foil on the board however, as you have already seen.

You have to be pretty quick when heating or the foil will lift and tear.

Good luck!
 
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Old 11-14-15, 08:01 AM
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Thank you....the foil is not ripped it just lifted. Am I still ok to proceed if it has been lifted? I do not have a solder wick or sucker. What would you recommend to heat the old solder to remove the old legs of the thermistor?
 
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Old 11-14-15, 08:24 AM
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In all likelihood, the old thermistor is broken (split) anyway, so put your needle nose pliers on one leg of the old thermistor, heat up the corresponding solder joint and pull out the lead. Repeat for the other side. If you're worried about the foil lifting, (after you've soldered the new thermistor in place) solder a wire to the new thermistor lead where it comes through the hole in the foil and solder the other end of the wire to another solder joint on the same trace. In essence, you're putting the wire in parallel with the trace.
 
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Old 11-14-15, 08:41 AM
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Thanks guys. The foil is already lifted and I have not removed the old legs yet. I tried removing with no heat and lifted the foil. Going to buy a soldering iron today. If I get everything put together from here on with no other bonehead moves, will the unit operate with the foil pulled away just a little bit?
 
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Old 11-14-15, 09:08 AM
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The unit will operate with the trace lifted. However, that will be a weak point on the trace, and with the amount of current that passes through the thermistor, there is a chance of the trace cracking/burning out at the point where it's lifted. That's why I suggested putting a piece of wire in parallel with the trace (that's what I would do).
 
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