DIYbanter - View Single Post - Microwave Oven

Jon Elson

wrote:

So my sister's uWave stopped cooking. Display normal hums and all that. I
have never been a microwave tech., actually never had one break. They
usually catch on fire after a while.

So is this indicating I got a leaky magnetron ? If I can get a cap foro
ten bucks I will fix it, but magnetrons are more expensive and this thing
is well, it is a nice, decent performing uWave oven. Not the best but I
have seen alot worse. The heat is even and the control system is not hard
to deal with. It is a Magic Chef, input power is stated as 1,500 watts, so
it is what, 1,300 ? Nice, small height wise but a bit wider than the
really small ones.

I just think when you got something good you should try to keep it going.
There is no money involved in this one.

The magnetron is a hot filament vacuum diode (at least as far as the power
supply is concerned). When you heat up the filament, it is supposed to
conduct electrons from the cathode to the anode (RF cavity). The common
failures are open or bad-burned filament, and copper hairs that short from
cathode to anode. You should be able to detect the hairs with a meter, the
heater can be tricky unless it just shows totally open. (sometimes the
filament has shorted in several places to the cathode, so it appears to be
OK (has low Ohms between the terminals) but it doesn't heat the cathode
effectively.) The cathode is connected to one of the filament terminals.

Jon