capacitor droppers and power factor

It does look like the circuit board in the main picture has R1 under the brown component. I think the 4 legged IC is likely a bridge rectifier.

RS bridge rectifier example

Martin C

I experienced the same or similar fault in a Honeywell heating controller, the circuit has 2 relays, 1 for heating and 1 for water, both independently switched as programmed.
If 1 relay was energised there was not enough power/voltage in the circuit to energise the 2nd relay.

Replacing the capacitor in the circuit restored correct functioning of the controller, cost was around £3 as against £80 for a new controller.

Emgee

The brown rectangular component is a film capacitor. I'd agree that the 4 legged IC is a low current bridge rectifier.

Andrew

John - thanks, that's not likely to be the problem then.

Martin - agreed, I think this is also probably still OK as I am getting output voltage.

I suppose next step is to desolder and test the electrolytic. If any of the surface mounted components are dead then it's probably game over.

I've got some capacitors that look like the Brown thingy except they're reddish-brown. Any markings on it.

If a capacitor, it's probably a suppressor. Next step is to trace out the board to find out what connects to what.

Are there 5 wires connected to the board or only 4. If 5, two reds?, you might have something like this:

I've said Low Vdc for the controller, but it might only be for the LED.

The components look too flimsy to be powering the motor, yet it connects to the mains on/off switch. Is it the only way power can get to the tool?

Dunno!

Dave

Andrew - Ok, so that could be a problem then. Can you suggest which capacitor might be performing which function and whether it failing would cause high voltage DC on the output?

Dave - This isn't the motor controller, it only does the LED. Takes 2 wire 240v input (RHS of insert pic labelled L & N) and presumably is supposed to give out low voltage DC on the two wires to left labelled + & -.

No, I dunno either, web search gives lots of possible circuits but which this is I'm not sure.

If the circuit includes a capacitor dropper it'll be the brown device that is doing it. The electrolytic will not like AC up it (see note below). I'd hazard a guess that the brown component is dropping some AC voltage, the bridge rectifier is operating at a low AC voltage and the electrolytic is smoothing the bridge output. Although I wouldn't have thought that the electrolytic was really needed. Any flicker will be at 100Hz and probably not be visible.

Andrew

Note: When I was in the apprentice hostel at RAE Farnborough one of the other students had the bright idea of seeing what would happen if you put a large metal can electrolytic across the mains. The answer is that it goes bang in a big way and spews its guts out. As a precaution the perpetrator put his motorcycle helmet over the capacitor. The paper and electrolyte that came out made rather a mess of the inside of his helmet.

Right, thanks. Further investigation to follow, although it occured to me last night that I might be better off gutting a GU10 LED spotlight and using the bits from that, after all if the original failed once it may fail again even if I repair it.

In the good old days I had a cheap and cheerful 1950s valve amplifier which had series heaters and a dropper capacitor to run them from mains voltage. One day the sound became increasingly distorted so I peered in the back, just in time to see the valves light up like searchlights and go out while the capacitor went SCHPOOO!! and ejected a quantity of brown liquid, fortunately not in my direction.

I replaced the valves with 6.3 volt equivalents and wired them in parallel to a transformer. No more problems.

George B.