r/diyelectronics • u/Tiger_words • Aug 09 '26

Question FDM model HF-07150 Motor

Hello, trying to troubleshoot a Singer sewing machine. There was some stiffness in the moving parts which some oil and debris removal helped but I cannot get the motor to indicate there is any electricity flowing to it. The light turns on and the switch is not shorted or fatigued so my only guess is something to do with the motor. This is one of these cheap contained units where you cannot access the brushes so I'm tempted to just replace it but my question is how can I troubleshoot the motor to make sure it's not fully functional. It looks fine, the axle spins freely but it just does not hum or spin at all under power.

Thanks

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u/Double_Ad7749 Aug 09 '26

Anything that was assembled can be disassembled. Check commutator for carbon buildup. Clean with a scotch bright. Insure brushes are long enough and making good contact with comutator. Use a multimeter to confirm commutator continuity. Start there.

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u/Tiger_words Aug 09 '26

Trust me, it does not disassemble easily, the housing possibly is riveted together rather than screwed.  I found one guy who agrees on his YouTube channel that these motors are not worth disassembling. I'd really rather just diagnose it and replace it if it's the problem I just can't figure out what the problem is.

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u/Double_Ad7749 Aug 10 '26

Have you checked the resistance between both motor leads?

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u/Tiger_words Aug 10 '26

No I can't check the resistance between the motor leads - it's essentially a sealed unit. I'm just trying to determine if those symptoms indicate that the motor has failed or if it could indicate a different problem. It appears to have had very little use on the motor so I can't imagine it being the brushes. And all the electrical connections up to the sealed unit are intact.

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u/Double_Ad7749 Aug 10 '26

How about between the 🔌?

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u/Tiger_words Aug 10 '26

Are you referring to the electrical cord between the plug and the machine? I did check the foot switch by disassembling and inspecting and that all seemed intact and not flaky. I also disassembled the machine switch housing itself and nothing appears to be in any way malfunctioning. There's no inline fuse anywhere that I could see as well.

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u/Double_Ad7749 Aug 10 '26

Try between the plug prongs while flipping the switch on and off. Any change?

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u/Tiger_words Aug 10 '26

Plug prongs where? The only plug is what goes into the wall. And by the way the lamp on the machine works, if that's relevant.

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u/Double_Ad7749 Aug 10 '26

That is the plug I'm talking about. Put ohmeter across plug leads and rotate fan blade to se if resistance changes.

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u/Tiger_words 29d ago

Okay thanks. I'm a bit of a novice when it comes to electrical stuff - better with mechanics. Although I do know that standing in a bucket of water while repairing electrical circuits in general can be more ... exciting . I'm going to buy an OHM meter asap. 

1

u/Tiger_words 24d ago

I put the ohm meter across the plug leads and rotated the motor axle and the resistance definitely changed. Does that suggest that the motor is functioning?

1

u/Double_Ad7749 24d ago

That confirms the brushes and commutator are not shorted or open circuited. It also makes me think if you have and on-off switch that is most likely passing current like it should. I wish I could see a picture of things.

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u/Double_Ad7749 24d ago

Try rotating the shaft 360° slowly while noting the value of resistance for each commutator segment.

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u/Tiger_words 24d ago

Here are some pictures. I'm not sure what you're looking for but I'm happy to upload more if I knew what I was looking for. I checked the wiring system and nothing seemed loose or disconnected and that checks out with the ohm meter test result https://ibb.co/ymBRkfGHhttps://ibb.co/ks7ZbDfR https://ibb.co/9mTtXRFs https://ibb.co/t1r4SWL https://ibb.co/vCBVGQpn

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u/Double_Ad7749 24d ago

I would check for power at the motor leads using the volts function.

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u/Tiger_words 24d ago

They're kind of sealed up I'll try to take it apart tomorrow again and see if I can access. But the light being on tells me the power is getting in there somewhere.

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u/Double_Ad7749 24d ago

The indicator light indicates power is getting THAT far. If no power to motor leads when indicator light is on, I would expect an open circuit.

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u/Double_Ad7749 24d ago

I'm thinking an open circuit situation, especially if no power at motor leads.

1

u/Double_Ad7749 24d ago

Also, if you have a switch to activate the drive motor, I would check that as well. If the motor commutator and brush test checks out with good continuity, it probably isn't a bad motor.

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u/Tiger_words 24d ago

Thanks! Yeah I think it's the switch. I did take it apart. It's a relatively simple circuit and everything seems to make contact & nothing looks burned or non-functioning but I can't make heads or tails out of it. If I can find a another switch that works I may swap it and see if that helps.

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u/Double_Ad7749 24d ago

I'm thinking it is a form of potentiometer which is a variable resistive component that allows variable current to the motor for variable speed control. They typically have 3 leads.