Microwave Oven - Interesting

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

But anyway I am hep to it, the capacitor goes bad alot, sometimes the magne tron. Sometimes triac, relay or something on the board comes loose off the solder. Normal shit.

So, I break out the old B&K 177 which has a 4 KV AC scale. The cap is rated 2,100 VAC.

I read the side with the rectifier and it is around a thousand volts. In fa ct less I think. I am thinking that is low. Put pur the probe on the transf ormer side and got an arc ! WTF ? And nothing happened. I chesked the meter , turned it to low AC and putting my finger on the probe made it read. Swit ched to ohms and that read as well.

So I do it again and I DID get a different result. I went to the magnetron side of the caps and got about the same reading, and then when I went to th e transformer side my computer started making all kinds of noise. I do not mean 60 Hz noise, this was like a digital stream noise, probably square wav es at more than one frequency.

Y'know the other day at work I got this unit the owner described as having multiple erratic and spontaneous operations. I decided to be a smartass and wrote it up as :

Complaint : Customer says multiple erratic/spontaneous operations.

Diagnosis : Unit needs exorcism.

Solution : Due to lack of holy water and Catholic Priest, changed main boar d.

I shit you not. But I could not blow it off because we are factory service.

Anyway, back to this uWave. On my tester, which tests at 400 mV/360 ohms im pedance, the cap checks pretty good. Little bit of curve at the tips of the triangle wave but for a 0.98 uF that is to be expected with these test par ameters.

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 w ell, it is a nice, decent performing uWave oven. Not the best but I have seen alot worse. The heat is even and the control s ystem is not hard to deal with. It is a Magic Chef, input power is stated a s 1,500 watts, so it is what, 1,300 ? Nice, small height wise but a bit wid er than the really small ones.

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

Reply to
jurb6006
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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

Reply to
Jon Elson

clamp on probes or meters are wonderful devices and much safer working hot. check heater current and HV current.

Jamie

Reply to
M Philbrook

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