Ulysses wrote:
Hi everyone. I read many web sites about testing and repairing
microwave ovens and have concluded that my Sharp microwave has a bad
diode and capacitor. I checked the magnetron and, according to what
I read, it's probably OK as I get a reading of about .4 ohms across
the terminals and it is not shorted to the case. However, I'm
wondering if it is possible to test the magnetron with low voltage
DC. I assume that what is usually fed into it is 120 VAC rectified
which I think will result in about 170 VDC. If that's the case, then
could 12 VDC be used just to verify the magnetron still works before
spending money on other parts? I ain't gonna do nothin' 'les someone
says it's OK and explains how ;-) The sympton right now is that it
buzzes and blows the fuse so I'm thinking an open diode and shorted
capacitor results in feeding 60 Hz AC to the magnetron thus causing
the buzz. Does that sound right?

Not even remotely close. Magnetrons work at around five thousand volts
after the doubler circuit; I don't know where you got the 170VDC figure
from.

Read Sam's guide and then ask over at sci.electronics.repair to get some
advice from guys that do this every day.

Sam's guide: http://www.repairfaq.org/sam/micfaq.htm

Note: Cautions about killing yourself by mucking around inside of a
microwave oven are neither unfounded nor exaggerated.

Jon

"Jon Danniken" wrote in message
...
Ulysses wrote:
Hi everyone. I read many web sites about testing and repairing
microwave ovens and have concluded that my Sharp microwave has a bad
diode and capacitor. I checked the magnetron and, according to what
I read, it's probably OK as I get a reading of about .4 ohms across
the terminals and it is not shorted to the case. However, I'm
wondering if it is possible to test the magnetron with low voltage
DC. I assume that what is usually fed into it is 120 VAC rectified
which I think will result in about 170 VDC. If that's the case, then
could 12 VDC be used just to verify the magnetron still works before
spending money on other parts? I ain't gonna do nothin' 'les someone
says it's OK and explains how ;-) The sympton right now is that it
buzzes and blows the fuse so I'm thinking an open diode and shorted
capacitor results in feeding 60 Hz AC to the magnetron thus causing
the buzz. Does that sound right?

Not even remotely close. Which part is not even close? All of it?
Magnetrons work at around five thousand volts after the doubler circuit; I
don't know where you got the 170VDC figure from.


I've measured rectified 120 VAC in the past and seem to recall it read about
170 VDC.

Read Sam's guide and then ask over at sci.electronics.repair to get some
advice from guys that do this every day.

Sam's guide: http://www.repairfaq.org/sam/micfaq.htm

Note: Cautions about killing yourself by mucking around inside of a
microwave oven are neither unfounded nor exaggerated.

Jon

"Ulysses" wrote in message
...

Not even remotely close. Which part is not even close? All of it?
Magnetrons work at around five thousand volts after the doubler circuit;
I don't know where you got the 170VDC figure from.


I've measured rectified 120 VAC in the past and seem to recall it read
about 170 VDC.


Does the word transformer mean anything to you except for the movie ?

The 120 volt line voltage is not rectified in the microwave.
There is a transformer in the microwave that changes the voltage to over
1000 volts and then it is rectified. Most common meters will not measure
voltages that high. The voltage can puncture the insulation of the meter
and kill you.

On Sun, 4 Jul 2010 10:51:19 -0700, "Ulysses" wrote:


"Jon Danniken" wrote in message
...
Ulysses wrote:
Hi everyone. I read many web sites about testing and repairing
microwave ovens and have concluded that my Sharp microwave has a bad
diode and capacitor. I checked the magnetron and, according to what
I read, it's probably OK as I get a reading of about .4 ohms across
the terminals and it is not shorted to the case. However, I'm
wondering if it is possible to test the magnetron with low voltage
DC. I assume that what is usually fed into it is 120 VAC rectified
which I think will result in about 170 VDC. If that's the case, then
could 12 VDC be used just to verify the magnetron still works before
spending money on other parts? I ain't gonna do nothin' 'les someone
says it's OK and explains how ;-) The sympton right now is that it
buzzes and blows the fuse so I'm thinking an open diode and shorted
capacitor results in feeding 60 Hz AC to the magnetron thus causing
the buzz. Does that sound right?

Not even remotely close. Which part is not even close? All of it?
Magnetrons work at around five thousand volts after the doubler circuit; I
don't know where you got the 170VDC figure from.


I've measured rectified 120 VAC in the past and seem to recall it read about
170 VDC.

120V is the RMS value. Yes, the peak voltage is about 170V.

V(RMS) * sqrt(2) = V(Peak).

...

On Jul 4, 2:43*am, "Jon Danniken"
wrote:
Ulysses wrote:
Hi everyone. *I read many web sites about testing and repairing
microwave ovens and have concluded that my Sharp microwave has a bad
diode and capacitor. *I checked the magnetron and, according to what
I read, it's probably OK as I get a reading of about .4 ohms across
the terminals and it is not shorted to the case. *However, I'm
wondering if it is possible to test the magnetron with low voltage
DC. *I assume that what is usually fed into it is 120 VAC rectified
which I think will result in about 170 VDC. *If that's the case, then
could 12 VDC be used just to verify the magnetron still works before
spending money on other parts? *I ain't gonna do nothin' 'les someone
says it's OK and explains how ;-) *The sympton right now is that it
buzzes and blows the fuse so I'm thinking an open diode and shorted
capacitor results in feeding 60 Hz AC to the magnetron thus causing
the buzz. *Does that sound right?

Not even remotely close. *Magnetrons work at around five thousand volts
after the doubler circuit; I don't know where you got the 170VDC figure
from.

Read Sam's guide and then ask over at sci.electronics.repair to get some
advice from guys that do this every day.

Sam's guide:http://www.repairfaq.org/sam/micfaq.htm

Note: Cautions about killing yourself by mucking around inside of a
microwave oven are neither unfounded nor exaggerated.

Jon

http://en.wikipedia.org/wiki/Harry_Boot

"Jon Danniken" wrote in message
...
Read Sam's guide and then ask over at sci.electronics.repair to get some
advice from guys that do this every day.

Sam's guide: http://www.repairfaq.org/sam/micfaq.htm

Wow, that site is a lot better than anything else I found. Thanks!

"Ralph Mowery" wrote in message
m...

"Ulysses" wrote in message
...
Does the word transformer mean anything to you except for the movie ?

The 120 volt line voltage is not rectified in the microwave.
There is a transformer in the microwave that changes the voltage to over
1000 volts and then it is rectified. Most common meters will not measure
voltages that high. The voltage can puncture the insulation of the meter
and kill you.

Thank you. I'll keep an eye on the beast. I have no intention of working
on my microwave oven while it's plugged in or on. I did not need to
discharge the capacitor because it is shorted. But I still don't trust it.

On Jul 4, 6:34*pm, "Ulysses" wrote:
"Ralph Mowery" wrote in message

m...



"Ulysses" wrote in message
...
Does the word transformer mean anything to you except for the movie ?

The 120 volt line voltage is not rectified in the microwave.
There is a transformer in the microwave that changes the voltage to over
1000 volts and then it is rectified. *Most common meters will not measure
voltages that high. *The voltage can puncture the insulation of the meter
and kill you.

Thank you. *I'll keep an eye on the beast. *I have no intention of working
on my microwave oven while it's plugged in or on. *I did not need to
discharge the capacitor because it is shorted. *But I still don't trust it.

How are you sure the capacitor is shorted??? Unless you have a very
small capacitor, it will look like a short to most voltmeters.