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Microwave Oven - Interesting
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jurb...@gmail.com
Mar 24, 2016, 9:18:47 PM3/24/16
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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.
But anyway I am hep to it, the capacitor goes bad alot, sometimes the magnetron. 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 fact less I think. I am thinking that is low. Put pur the probe on the transformer 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. Switched 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 the 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 waves 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 board.
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 impedance, 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 parameters.
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.
But anyway I am hep to it, the capacitor goes bad alot, sometimes the magnetron. 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 fact less I think. I am thinking that is low. Put pur the probe on the transformer 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. Switched 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 the 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 waves 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 board.
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 impedance, 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 parameters.
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.
Jon Elson
Mar 25, 2016, 12:06:20 AM3/25/16
to
jurb...@gmail.com 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 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
> 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.
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
M Philbrook
Mar 26, 2016, 2:26:13 PM3/26/16
to
In article <a0996009-e50c-4562...@googlegroups.com>,
jurb...@gmail.com says...
clamp on probes or meters are wonderful devices and much safer working
hot.
check heater current and HV current.
Jamie
jurb...@gmail.com says...
hot.
check heater current and HV current.
Jamie
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