Sewing machine electronic style foot controller

roytom

I’m attempting to repair a foot control for an ELNA Club 500 Sewing Machine. This is an electronic machine that uses a foot control that just passes a signal to the machine, not mains voltage. It uses a tiny
rheostat. The wire to the foot control is damaged causing the machine to run at maximum speed. Therefore the wire needs replacing.

I found a YouTube vid that covers this but still can’t get it right.

The original wire has a screen and red and white wires. But the nearest I could get was a thinner audio cable (Maplins) that’s screened but has a blue wire instead of the white (as per the original).

In making the replacement I’ve checked everything but it causes the machine to always run even when in the stop position, but it goes faster as the rheostat is moved to max speed. Using an ohm meter I’ve checked the rheostat but can’t find a problem with it. I also cannot find any cross leakage between the wires or screen.

I can’t find any reason for this. Am I using the wrong sort of wire?would all audio cables cause the same problem?

Thanks

wongataa

The type of wire wouldn't make a difference (unless it couldn't cope with the current and shorted/melted/smoked). Either you wired it incorrectly or the fault is not in the wire you replaced. Maybe the faulty wire caused an issue somewhere else?

that

at a guess, being just a variable resistor/rheostat, these always have 2 or 3 connectors unless ganged up like a volume control in a stereo amp.

I would think that you could have got away 3 wire mains cable.... at a push, but it is probably thicker.

I think you got the colours mixed up? Resistors fall as an open circuit, or intermittently open circuit.

EDIT: Just looking at this, there is a capacitor, if that fails it will make the unit run at full speed... cut its lead as suggested below
https://www.youtube.com/watch?v=WIJYRAkkRqY

EDIT 2: https://www.youtube.com/watch?v=kEDLc1kGzEw

roytom

Thanks for the suggestions and vids.
Yes I removed the capacitor already before I replaced the wire and now I accept the wire is probably not the cause of this problem.
But further testing reveals the blue wire (located on its own at the -off end- of the slider) isnt doing anything at all as when I disconnected it the behaviour is the same.
Either theres something wrong with the connection on the rheostat or at the jack plug end - the socket on the machine is a nightmare to get at to check.
Btw the track/strip of the rheostat at the -on end- the screen connection is parallel with the blue wire (which is not doing anything). The red is aligned with the lower track where there is no connection at the far end.


https://imgur.com/gallery/RIGVQ

that

besides the photobucket pic not showing, the post also has !!! which makes it hard to understand.

on https://www.youtube.com/watch?v=kEDLc1kGzEw about 31 seconds in, the bottom wiring diagram shows that the resistor is only connected via 2 wires, and this controls the voltage to one set of coils on the motor.

If it is an audio jack plug attachment to the machine, the jack plug socket on the machine could be faulty, and the wiring set to bypass the foot peddle?

I do not know how the original wires were connected, but for safety reasons assume the screen on the original was earthed as to trip the fuse should should the live wire insulation fail and it would short to it.

If the machine runs on switch on, depress the peddle, and if it stops then the wires positions have been switched, and are the wrong way around

roytom

Ta. All things noted. The pic should be viewable now, if not I will do it again. See below.

Indeed the jack socket on the machine could be faulty. Or a computer fault with the machine?


The wiring is exactly as originally done. What I need now is a rheostat to test this out as an alternative.

https://imgur.com/gallery/RIGVQ

that

That motor circuit is a Very old fashioned, simple circuit. There is no computer that connects to the motor, just the foot peddle, similar to an old style light dimmer that divides voltage.

If the rheostat was burnt out then it would be dead. It could be the arm is not moving and stuck on full power.

These rheostats are often wound resistance wire. Of the opinion a 2 wire light dimmer would suffice as a temporary rheostat for testing.

Photobucket is still killing your pics, use https://imgur.com

roytom

Brill, thanks for all the info etc.

But this machine is electronic, it hasn not got a mains powered foot control like older machines and some new mechanical ones. This is an early version of an electronic machine and the device just is used to convey signals not mains current.

Therefore this little device with a slider is a variable resistor? Is that the term? Sorry I have probably described it wrongly. I wonder where I could get an alternative one to try out, especially now Maplins is fading fast.

Thanks for alternative to the irritating photobucket. I will get stuck into that.

https://imgur.com/gallery/RIGVQ

roytom

I have now found this as a possible replacement - potentiometer, sorry I described it wrongly before.

Please see below

roytom

What I think I need is a replacement slide potentiometer. RS Components has one described as
Bourns PTA Series Potentiometer, 10k ohm, ±20%, 0.1W, Through Hole
RS Stock No. 737-7776 Mfr. Part No. PTA2043-2015DPB103 Brand Bourns

The existing one is 35mm long 7mm wide and 5.5mm deep approximately.
It has a code on it 89501 10KA

Please forgive my ignorance but would this be a possible match?

Thanks again

Le_Kirk

The one you refer to (this link) is 35 x 9 x 5.5 and if you follow this link you will find the data sheet and be able to check every dimension. I would imagine they are both 10 K Ohms according to part numbers.