Author Topic: sewing machine pedal repair  (Read 601 times)

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Offline m3vuvTopic starter

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sewing machine pedal repair
« on: September 30, 2021, 02:44:06 pm »
Hi all,i have a singer 2502c sewing machine,the issue is with the foot switch,it is either on or off,there is no ramp up of the power,its like flatout or nothing,so far i have tested the bt134 triac with a dmm,it seems fine,any ideas what the issue could be,would a duff cap or diac cause this?,i have measured the caps for s/c they are not shorted,not cheched capacitance yet or esr.attached is a pic of the pcb,have no idea of the history as just brought it for spares or repair. tia
























 

Offline m3vuvTopic starter

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Re: sewing machine pedal repair
« Reply #1 on: September 30, 2021, 02:47:12 pm »
would i be right in thinking the caps gowing low in capacitance ,ie the one that feeds the diac would cause the non ramp up of motor speed?,tia .
 

Offline dark_hawk

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Re: sewing machine pedal repair
« Reply #2 on: September 30, 2021, 02:54:55 pm »
Have you checked the switch/potentiometer?
 

Offline m3vuvTopic starter

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Re: sewing machine pedal repair
« Reply #3 on: September 30, 2021, 03:11:42 pm »
the switch is fine as are is potentiometer/trimmer.i imagine the cap that feeds the diac has gone low in capacitance so it fires the triac fully on strait away without any delay as to my mind i can see that being the issue that could cause this??.
 

Offline m3vuvTopic starter

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Re: sewing machine pedal repair
« Reply #4 on: September 30, 2021, 03:45:39 pm »
would i be right in thinking the caps gowing low in capacitance ,ie the one that feeds the diac would cause the non ramp up of motor speed?,tia .
 

Offline TimFox

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Re: sewing machine pedal repair
« Reply #5 on: September 30, 2021, 04:44:29 pm »
The orange capacitors are film units, so they are unlikely to change capacitance but they could fail.  I would guess that if it be a component value change problem (as opposed to open/short failure), the resistors are more likely culprits.
 

Offline CatalinaWOW

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Re: sewing machine pedal repair
« Reply #6 on: September 30, 2021, 05:06:08 pm »
Holes in the PWB are extremely large.  All mechanical support for the passive components is solder.  How do those joints look on the other side of the board?  Any fractures?
 

Offline jpanhalt

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Re: sewing machine pedal repair
« Reply #7 on: September 30, 2021, 06:00:05 pm »
I wouldn't expect the potentiometer in the foot control to be a "trimmer." 

At the input to the board what does it read?  My Pfaff reads from about 20K to 1K, depending on how much I push the pedal down.  Between those values, it is either OFF or fully on, which reads a bit less than 1k.

Instead of "OK," what resistances did you read?
 


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