Electronics > Repair
Sewing machine power board
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DeepLink:

--- Quote from: Robert A on October 02, 2024, 01:35:09 pm ---Thanks for the info. C50 was a Rifa capacitor which had blown, I guess took R10 with it and hopefully nothing else. I’ve removed D85 and T114 tests good, so looks like we’re ok.

--- End quote ---

Failure in C50 should not blow R10
coromonadalix:
the motor rotor should be visually checked  ...
Whales:

--- Quote from: DeepLink on October 02, 2024, 03:40:56 pm ---
--- Quote from: Robert A on October 02, 2024, 01:35:09 pm ---Thanks for the info. C50 was a Rifa capacitor which had blown, I guess took R10 with it and hopefully nothing else. I’ve removed D85 and T114 tests good, so looks like we’re ok.

--- End quote ---

Failure in C50 should not blow R10

--- End quote ---

Agreed.

There's a chance C50 could also be a symptom of the problem that blew R10 (mains overvoltage?), but I'm not sure.  Was the RIFA one of the clear types, or a more modern RIFA?



--- Quote from: coromonadalix on October 02, 2024, 03:47:24 pm ---the motor rotor should be visually checked  ...

--- End quote ---

A shorted motor could have caused the resistor to blow.  Opening it for visual inspection would be really good, but some motors make that difficult.  You might also be able to try connecting it to a bench power supply and seeing if it makes strange noises or gets really hot when running with no mechanical load.  But that might not be a completely conclusive test.

It would be worth running the repaired circuit with the motor unplugged, to make sure no other parts are bad.  Then turn it off, plug the motor back in, turn it on again and see what happens. 

(Again I'll hazard that all parts of the motor driving circuitry are at mains referenced potential, dangerous to touch, unplug the whole machine from the wall before doing any of this).
Robert A:

--- Quote from: Whales on October 02, 2024, 11:13:56 pm ---
--- Quote from: DeepLink on October 02, 2024, 03:40:56 pm ---
--- Quote from: Robert A on October 02, 2024, 01:35:09 pm ---Thanks for the info. C50 was a Rifa capacitor which had blown, I guess took R10 with it and hopefully nothing else. I’ve removed D85 and T114 tests good, so looks like we’re ok.

--- End quote ---

Failure in C50 should not blow R10

--- End quote ---

Agreed.

There's a chance C50 could also be a symptom of the problem that blew R10 (mains overvoltage?), but I'm not sure.  Was the RIFA one of the clear types, or a more modern RIFA?



--- Quote from: coromonadalix on October 02, 2024, 03:47:24 pm ---the motor rotor should be visually checked  ...

--- End quote ---

A shorted motor could have caused the resistor to blow.  Opening it for visual inspection would be really good, but some motors make that difficult.  You might also be able to try connecting it to a bench power supply and seeing if it makes strange noises or gets really hot when running with no mechanical load.  But that might not be a completely conclusive test.

It would be worth running the repaired circuit with the motor unplugged, to make sure no  :-+other parts are bad.  Then turn it off, plug the motor back in, turn it on again and see what happens. 

(Again I'll hazard that all parts of the motor driving circuitry are at mains referenced potential, dangerous to touch, unplug the whole machine from the wall before doing any of this).

--- End quote ---

It was a clear Rifa, spilled it’s guts all over the place  :palm:

I did do a quick resistance test across the poles of the motor which didn’t show any zero or very low ohms readings. Good idea using a separate power supply to test the motor.   :-+
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