Reluctant starter - intermittent.

[wristpin]

I've had this little fret saw for around 40 years and about a year ago it occasionally refused to start unless I spun the spindle - just hummed. I fitted a new capacitor and it appeared to cure it - for a while. Sometimes it would start and other times refused but I've discovered that with a light tap on the chassis - away it goes. So I'm guessing that the "little back box" is some sort of mechanical relay to fire off the capacitor and that it is a bit sticky.
Googling Magnetic Devices suggests that that company is no longer trading - what is the correct name for it and where am I likely to get one?

 

[daleyd]

Do you have a sketch as to how it connects to the capacitor and windings?

I've not done much with single phase motors, but they normally have some sort of centrifugal switch to switch out the cap when up to speed. I'd guess it's either instead of, or something to do with this.

 

[rtbcomp]

Looks like a current sensing relay

Once the motor is up to speed and the current on the main winding settled down, the relay will drop out and disconnect the start winding.

 

[rtbcomp]

I think I'm right in saying that fridge motors use a similar system, so one off an old fridge might work.

 

[brightspark]

I think I'm right in saying that fridge motors use a similar system, so one off an old fridge might work.

yes the old ones did and freezers. a nip down the councill tip and rob one or 2 of an old one while the staff -- dorks arent looking