Knee-operated singer sewing machine 99K - UK Vintage Radio Repair and Restoration Discussion Forum

Mgtstan · 22nd Aug 2021, 8:58 pm

My 1950 knee-operated singer has lost the ability to moderate its speed i.e. if you plug it in, it goes fast, and the only way to stop it is to unplug it.

You have threads about foot-operated versions. Any thoughts on how a knee-operated machine can be restored to functionalilty?

Graham G3ZVT · 22nd Aug 2021, 10:03 pm

Hi there and welcome to the forum.
My 99K has the more common foot controller but looking at this knee controller image on line, it looks to me that it is likely to be electrically identical to the foot controller.

Click image for larger version

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No doubt you have seen other threads where the cause of the speed being stuck at maximum is a shorted capacitor inside the controller, so unplug the machine, unscrew the case of the controller snip out the capacitor, reassemble and test.

It will work fine without the capacitor it will just wipe out your neighbours AM radios, if you care (of course you care) let us know once you have restored the speed control, and we can help you source a replacement capacitor.

paulsherwin · 22nd Aug 2021, 10:32 pm

Yes, the knee controller is basically the same as the more common foot pedal, and it's very common for the suppression capacitors to fail. Just replace them with modern class X2 types.

Mgtstan · 3rd Sep 2021, 4:25 pm

Thanks for your help.

I agree that the theory is the same as a foot pedal, but the physical layout is different.

The kneebar is connected to a mechanism that sits in the box to the right of the main machine. This appears to be purely mechanical, and I don't see a capacitor there.

The motor has a section added on to the outside, and I am attaching a picture of what you can see inside. Is this the capacitor?

3 pictures attached.
- kneebar mechanism - I have 2 of them!
- motor and attachment
- attachment interior

Many thanks.

Station X · 3rd Sep 2021, 4:40 pm

The printed label suggests the component is a dual capacitor. A clearer picture of the label would help. It looks easy enough to disconnect it rather than snip it out.

Might be worth drawing out the circuit.

Nickthedentist · 3rd Sep 2021, 5:09 pm

That’s a triple capacitor, 80nF & 80nF & 4nF, from what I can make out from the slightly blurry photo.

JonSnell · 5th Sep 2021, 4:46 pm

The triple capacitor is an interference suppressor to allow the family a view of the 405 line television without too much interference and noise.

My 99 has two capacitors in the foot pedal for exactly the same reason. One of them shorted and I was either fast or faster!

Replaced them with two 100n Class X axials.

Mgtstan · 9th Sep 2021, 10:44 pm

Thanks everyone. I disconnected the capacitor unit, and functionality has been restored.

22nd Aug 2021, 8:58 pm	#1
Mgtstan Diode Join Date: Aug 2021 Location: Dundee, Scotland, UK. Posts: 3	Knee-operated singer sewing machine 99K My 1950 knee-operated singer has lost the ability to moderate its speed i.e. if you plug it in, it goes fast, and the only way to stop it is to unplug it. You have threads about foot-operated versions. Any thoughts on how a knee-operated machine can be restored to functionalilty?

22nd Aug 2021, 10:03 pm	#2
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,710	Re: Knee-operated singer sewing machine 99K Hi there and welcome to the forum. My 99K has the more common foot controller but looking at this knee controller image on line, it looks to me that it is likely to be electrically identical to the foot controller. No doubt you have seen other threads where the cause of the speed being stuck at maximum is a shorted capacitor inside the controller, so unplug the machine, unscrew the case of the controller snip out the capacitor, reassemble and test. It will work fine without the capacitor it will just wipe out your neighbours AM radios, if you care (of course you care) let us know once you have restored the speed control, and we can help you source a replacement capacitor. __________________ -- Graham. G3ZVT Last edited by Graham G3ZVT; 22nd Aug 2021 at 10:08 pm.

22nd Aug 2021, 10:32 pm	#3
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,929	Re: Knee-operated singer sewing machine 99K Yes, the knee controller is basically the same as the more common foot pedal, and it's very common for the suppression capacitors to fail. Just replace them with modern class X2 types.

3rd Sep 2021, 4:25 pm	#4
Mgtstan Diode Join Date: Aug 2021 Location: Dundee, Scotland, UK. Posts: 3	Re: Knee-operated singer sewing machine 99K Thanks for your help. I agree that the theory is the same as a foot pedal, but the physical layout is different. The kneebar is connected to a mechanism that sits in the box to the right of the main machine. This appears to be purely mechanical, and I don't see a capacitor there. The motor has a section added on to the outside, and I am attaching a picture of what you can see inside. Is this the capacitor? 3 pictures attached. - kneebar mechanism - I have 2 of them! - motor and attachment - attachment interior Many thanks. Attached Thumbnails

3rd Sep 2021, 4:40 pm	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,286	Re: Knee-operated singer sewing machine 99K The printed label suggests the component is a dual capacitor. A clearer picture of the label would help. It looks easy enough to disconnect it rather than snip it out. Might be worth drawing out the circuit. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

3rd Sep 2021, 5:09 pm	#6
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,840	Re: Knee-operated singer sewing machine 99K That’s a triple capacitor, 80nF & 80nF & 4nF, from what I can make out from the slightly blurry photo.

5th Sep 2021, 4:46 pm	#7
JonSnell Hexode Join Date: Oct 2019 Location: Weymouth, Dorset, UK. Posts: 475	Re: Knee-operated singer sewing machine 99K The triple capacitor is an interference suppressor to allow the family a view of the 405 line television without too much interference and noise. My 99 has two capacitors in the foot pedal for exactly the same reason. One of them shorted and I was either fast or faster! Replaced them with two 100n Class X axials. __________________ Valve equipment repairs since 1968 https://jonsnell.co.uk

9th Sep 2021, 10:44 pm	#8
Mgtstan Diode Join Date: Aug 2021 Location: Dundee, Scotland, UK. Posts: 3	Re: Knee-operated singer sewing machine 99K Thanks everyone. I disconnected the capacitor unit, and functionality has been restored.