Another Rifa Smoke Bomb - UK Vintage Radio Repair and Restoration Discussion Forum

cathoderay57 · 6th Apr 2020, 3:53 pm

A plea for help was received from SWMBO. The electric sewing machine is running without the foot switch being depressed, and it's smoking. Opening it up revealed a Rifa suppressor capacitor across the switch contacts that had decided to become a smoke bomb. The last one that did that was on the mains switch of the Quad 22 control unit. Nasty little blighters - change on sight. A new Class X 0.1uF and we're back in business. Hopefully the new cap will last longer than the brownie points......

chriswood1900 · 6th Apr 2020, 5:08 pm

My wife had just the same on her Viking machine, she was impressed I could diagnose it from the smoke and the smell.
Easy fix once you can get to it.
Only thing you can say is wherever they crop up there will be problems, I always use the Panasonic ones to replace them and as yet have had no problems, whereas the Rifas were failing in my stock drawer before I could fit them!

paulsherwin · 6th Apr 2020, 5:46 pm

It's not only Rifas. This is quite a common fault on electric sewing machines of all ages. The mains suppression caps fail short circuit across the switches or pedal rheostat, and you come home to find the machine happily sewing away on its own. It does remind you to unplug it from the mains when not in use

Of course, X2 caps aren't supposed to fail short circuit...

Herald1360 · 6th Apr 2020, 6:33 pm

Presumably if they're across the switch rather than the mains, the current limit imposed by the motor limits the grunt available to blow the little sod to smithereens

Hartley118 · 6th Apr 2020, 6:38 pm

The RIFAs that are directly across the mains are easier. They self-destruct completely and need no further attention!

Martin

Refugee · 6th Apr 2020, 9:00 pm

Quote:

Originally Posted by Hartley118

The RIFAs that are directly across the mains are easier. They self-destruct completely and need no further attention!

Martin

They do cause a hunt for where the smell is coming from after it has finished self-destructing and making the smell.
Then the appliance continues to be used with the aftermath remaining inside it.

Silicon · 7th Apr 2020, 2:58 pm

You could probably improve the design by adding a Varistor across the mains and a snubber circuit across the motor.

6th Apr 2020, 3:53 pm	#1
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,384	Another Rifa Smoke Bomb A plea for help was received from SWMBO. The electric sewing machine is running without the foot switch being depressed, and it's smoking. Opening it up revealed a Rifa suppressor capacitor across the switch contacts that had decided to become a smoke bomb. The last one that did that was on the mains switch of the Quad 22 control unit. Nasty little blighters - change on sight. A new Class X 0.1uF and we're back in business. Hopefully the new cap will last longer than the brownie points...... Attached Thumbnails

6th Apr 2020, 5:08 pm	#2
chriswood1900 Octode Join Date: Jan 2007 Location: Dorridge, West Midlands, UK. Posts: 1,481	Re: Another Rifa Smoke Bomb My wife had just the same on her Viking machine, she was impressed I could diagnose it from the smoke and the smell. Easy fix once you can get to it. Only thing you can say is wherever they crop up there will be problems, I always use the Panasonic ones to replace them and as yet have had no problems, whereas the Rifas were failing in my stock drawer before I could fit them! __________________ Chris Wood BVWS Member

6th Apr 2020, 5:46 pm	#3
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,942	Re: Another Rifa Smoke Bomb It's not only Rifas. This is quite a common fault on electric sewing machines of all ages. The mains suppression caps fail short circuit across the switches or pedal rheostat, and you come home to find the machine happily sewing away on its own. It does remind you to unplug it from the mains when not in use Of course, X2 caps aren't supposed to fail short circuit...

6th Apr 2020, 6:33 pm	#4
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Another Rifa Smoke Bomb Presumably if they're across the switch rather than the mains, the current limit imposed by the motor limits the grunt available to blow the little sod to smithereens __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

6th Apr 2020, 6:38 pm	#5
Hartley118 Nonode Join Date: Aug 2015 Location: Cambridge, Cambs. UK. Posts: 2,198	Re: Another Rifa Smoke Bomb The RIFAs that are directly across the mains are easier. They self-destruct completely and need no further attention! Martin __________________ BVWS Member

7th Apr 2020, 2:58 pm	#7
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,163	Re: Another Rifa Smoke Bomb You could probably improve the design by adding a Varistor across the mains and a snubber circuit across the motor.