Basic Microwave Repair?
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 |
Basic Microwave Repair?
"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 |
Basic Microwave Repair?
"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. |
Basic Microwave Repair?
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). ... |
Basic Microwave Repair?
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 |
Basic Microwave Repair?
"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! |
Basic Microwave Repair?
"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. |
Basic Microwave Repair?
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. |
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