AEG Microwave repair

[CambridgeWorks]

Back in the 70s Bosch asked me to provide a local repair service for in and out of warranty domestic refrigeration products.
Their retail on a compressor was about 25% more than my usual Danfoss brand. However, they did give a 40% trade discount. They could afford to!
No doubt, things have changed a lot by now.
Rob

[boater sam]

The diode and capacitor are a doubler. I have never seen a microwave without, perhaps the diode was in the cap can. The idea of the doubler circuit is to save on transformer insulation and to reduce fault current on mag flash over I believe.

[Mike Watterson]

Also
https://www.circuitdiagram.co/microwave-...-diagrams/

[Mike Watterson]

The diode and capacitor are a doubler. I have never seen a microwave without, perhaps the diode was in the cap can. The idea of the doubler circuit is to save on transformer insulation and to reduce fault current on mag flash over I believe.

I shall investigate the cap and transformer. Certainly I expected a diode, though I think operation is possible without one.

I wonder what I could use the transformer for? A 500W Valve transmitter?

I'm sure a previous one I scrapped years earlier had the EHT rectifier.

[Radio Fixer]

Cant see how the diode makes it "a doubler"? To me you need two capacitors for that.

More on the subject here: https://www.vintage-radio.net/forum/show...p?t=201478

Post #5 is interesting.

Gary

[Refugee]

It is a doubler running into a short circuit. The magnatron runs off the second half cycle and produces the mocrowave power as it works like the second diode of the doubler and a sort of dropper both at once.

[Mike Watterson]

But the EHT diode is same way round as magnetron diode. A doubler with 2nd diode as short surely needs the EHT diode the other way round?
I'm confused.

Interesting discussion on the link.

Also I think I've only ever seen ones where the control panel died. I suppose if used a lot the magnetron filament will go low emission.

[Murphyv310]

It is a doubler circuit.
Sorry I had to look again at the circuit. The cap would not supply current after the initial charge unless the diode was the opposite way to the magnetron.
Remember the anode of the magnetron is at ground the filament is at HT Negative. There is NO shorts on the HT side.

[jimmc101]

Have to disagree there, the diode conducts when the transformer output is positive charging the capacitor to peak voltage.
When the xfmr output voltage is negative the capacitor voltage adds to this, driving the magnetron fliament/cathode negative by more than the voltage from the transformer alone.
I believe that the value of the capacitor is fairly critical and is used to set the output power from the magnetron.

On my old Panasonic oven the capacitor failed short producing a loud hum without blowing the fuse. The diode failed a few weeks later.

Jim

Just seen your update.

[Murphyv310]

Have to disagree there, the diode conducts when the transformer output is positive charging the capacitor to peak voltage.
When the xfmr output voltage is negative the capacitor voltage adds to this, driving the magnetron fliament/cathode negative by more than the voltage from the transformer alone.
I believe that the value of the capacitor is fairly critical and is used to set the output power from the magnetron.

Spot on!