I am a professional working on the field of electrical power engineering and I know what I’m doing.
During this repair you are dealing with 230VAC mains voltage which can be lethal if one gets electric shock from it. Always remember to detach the power plug when dealing with internal wiring. I shall not take any responsibility for any property damage or personal injuries which could occur during following this guide. If you don’t completely understand content of this guide, then don’t do repairing by yourself but instead ask some electrician to do it.
My mother told that her Bernina Record 830 sewing machine (from 70’s) started to make odd hissing and emitted weird odor from it’s motor compartment. I opened it and noticed that motor/RFI-interference capacitor pack was leaking. One might find new capacitor pack in the ebay, but thanks to Swiss engineering there is a schematics and component values printed on a capacitor pack so one can make a new pack out of separate capacitors. Capacitors need to be mains rated.
Two 2000pF (2nF) X1/Y2 capacitors
One 60nF (0.06uF) X1 capacitor (replaced this with 47nF)
One 20nF (0.02uF) X1 capacitor
Heat shrink tube or eletrical insulation tape to cover capacitor legs/soldering joints
Suitable insulated wire (I used 0.5mm diameter speaker wire altough it is not allowed for 230VAC installations, but still it is thicker and better insulated than machine’s original internal wires)
I managed to find all the capacitor’s from old CRT TV circuit board. I first tested the circuit by soldering them together in the air with test wires. For testing, I recommend to make extension cord in which 60 watt incandescent light is connected in series with sewing machine. This way, if there is a short circuit, one doesn’t blow a fuse or cause more damage to machine under repair. Machine worked perfectly with new capacitors, so I fitted them separately in the motor compartment and soldered new wires between them.
1. Final position for two 2000pF capacitors (blue ones)
2. Final position for the 20nF capacitor (the yellow one)
3. Final position for the 60nF capacitor (the red one)
Only problem was, that only place where 60nF capacitor would fit, is on the front side of the motor (when machine is placed in operating position). This prevents the installation of motor compartment cover (facing the machine chassis), so machine “loses” it’s double insulation (class 2 electrical appliance in EU area with so called “europlug”). Finger protection is on a same level than before.
It might be possible to install the 60nF capacitor in the hollow next to 20nF capacitor, but I didn’t want to do that, since in there it blocks the hole used to replace motor brushes. OK, the only disadvantage is that in case brushes have to be replaced, one has to open to motor compartment like in this repair, but still. My suggestion is to make a new plastic or plexiglass compartment on top of the motor compartment for new capacitors.
Also, there are wires going to lamp and to the bottom block so I wouldn’t count on the double insulation, considering this machine is made in the 70’s when regulations for electrical appliances were less strict compared nowadays regulations. I’m planning to convert this machine to class 1 appliance (protective earthed) by drilling a hole to machine’s chassis, installing earthing point to it and replacing the original 2-wire power cord with 3-wire earthed cord. I’m also going to buy stand-alone residual current device (RCD) to be used with the sewing machine.
Operational again. Let’s see if it’ll last next ~40 years with new caps. Under the sewing machine there is a broken subwoofer also waiting to be repaired.
Modified extension cord with E27-socket connected in series with AC outlets. Cord is meant for testing purposes only and it prevent’s blowing the fuse and doing more damage in appliance under repair in case of a short circuit.
As one can see, this extension cord is against electrical regulations even without bulb socket connected to it.
1. Powerplug is so called europlug meant to be used with double insulated class 2 appliances
2. Power cord is only single-insulated
3. Sockets are class 0 sockets with no protective earthing contact and meant to be used in dry areas only. With this kind of sockets, cord plug should be class 0 type with round shape so it won’t fit to class 1 wall sockets
For appliance classes, see Appliance classes in Wikipedia