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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Advice needed for microwave diagnosis
Your address does not show properly to have a direct answer. Use
something like for your address. This works well. You have to properly test the transformer, rectifier, and tube. You cannot do this by visual observation. One or a few of these devices are at fault. The best test is substitution, unless you have the equipment to actively test them. Even if you know what you are doing, it may work out cheaper to give the microwave out to a shop that fixes them all the time. They would have the parts to try, or the test gear to determine the exact failure. Sometimes servicing these yourself is more costly than giving it out. As for the knowledge you seem to safely know where you are going. -- Greetings, Jerry Greenberg GLG Technologies GLG ============================================== WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm Instruments http://www.zoom-one.com/glgtech.htm ============================================== wrote in message ... Hello all, YES, I'm -fully- aware of the dangers associated with HV and RF. The symptom is: about a couple of seconds after heating starts, one can hear a half second low hum then either heating stops or resumes normally, until another random occurence. In case where it abnormally stops, the control panel returns to the stanby state, just as if the STOP touch had been hit twice. Of course, I first thought of a bad switch in the door's interlocks, or some intermitent somewhere. Nope, all looks fine and, by the way it wouldn't cause the controller to return to stanby. I have checked as much as possible: -) the mains part is OK, no loose connection, no dying relay, no burnt thermal protection. -) the filament seems in good shape, no worn insulation, connectors fine. -) the diode works as expected (under a simple 15 V test @ 50 mA). -) the capacitor looks good, well: under low voltage test. -) the magnetron has no evidence at all of any arcing, loose internal filament connection or shortening, as far as I can see or test. -) the mains and HV fuses are in brand new condition. The symptom disappear completely when the HV circuit is open by disconnecting the HV transformer output. What seems more likely is that when symptom occurs (possibly due to intermittent shortening internal to the capacitor, hence the little hum) the HV is brought to its knees and the low voltage transformer being in undervoltage, the controller somehow "jumps" to iddle. However, I note that it doesn't go in the RESET state. Which test do you suggest to pinpoint the defective part more positively? I've thought of monitoring either the filament's current or the HV. But then how could I determine whether it is the filament that is arcing or shortening somehow, or the capacitor, or the magnetron that's the culprit? I don't think I have a suitable HV load to put in place of the magnetron for testing the thing in actual operation. Operating the beast with the magnetron's HV disconnected might create a deadly overvoltage situation if no load is connected. The best I can do is "borrow" the capacitor of my other oven (a 0.84 uF/1900V) and try it for a SHORT period. I'm a little reluctant at this, due to the sligtly inferior voltage rating (but I suspect it can't be hurt really if test is over a short period). For anyone asking gory details, my microwave oven is a Samsung type RE576TC produced in 1989. It is a 1050/600 W (absorbed/RF), is micro-controlled, uses magnetron Samsung 2M204-M3, a 0.91 uF/2100V capacitor and HVR-1X 3 diode. Thank you in advance for any hint. -- Here's where you can reach me (fixed-width font required). . ,-. . .. . ,-. ,-. ,-. ,-. |- /,-.\ ,-. ,-. ,-| ,-. ,-. ,-. | | `-. |-' | | |-' | |,-|| | | -- |-' -- | | | | | | | `-^ `-' `-' ' ' `-' `' \`-^' `-| `-' `-^ :; `-' ' `-| `-- | ,| ` `' |
#3
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Advice needed for microwave diagnosis
Go he
http://www.repairfaq.org/REPAIR/F_mi...tml#MICFAQ_015 wrote in message ... Hello all, YES, I'm -fully- aware of the dangers associated with HV and RF. The symptom is: about a couple of seconds after heating starts, one can hear a half second low hum then either heating stops or resumes normally, until another random occurence. In case where it abnormally stops, the control panel returns to the stanby state, just as if the STOP touch had been hit twice. Of course, I first thought of a bad switch in the door's interlocks, or some intermitent somewhere. Nope, all looks fine and, by the way it wouldn't cause the controller to return to stanby. I have checked as much as possible: -) the mains part is OK, no loose connection, no dying relay, no burnt thermal protection. -) the filament seems in good shape, no worn insulation, connectors fine. -) the diode works as expected (under a simple 15 V test @ 50 mA). -) the capacitor looks good, well: under low voltage test. -) the magnetron has no evidence at all of any arcing, loose internal filament connection or shortening, as far as I can see or test. -) the mains and HV fuses are in brand new condition. The symptom disappear completely when the HV circuit is open by disconnecting the HV transformer output. What seems more likely is that when symptom occurs (possibly due to intermittent shortening internal to the capacitor, hence the little hum) the HV is brought to its knees and the low voltage transformer being in undervoltage, the controller somehow "jumps" to iddle. However, I note that it doesn't go in the RESET state. Which test do you suggest to pinpoint the defective part more positively? I've thought of monitoring either the filament's current or the HV. But then how could I determine whether it is the filament that is arcing or shortening somehow, or the capacitor, or the magnetron that's the culprit? I don't think I have a suitable HV load to put in place of the magnetron for testing the thing in actual operation. Operating the beast with the magnetron's HV disconnected might create a deadly overvoltage situation if no load is connected. The best I can do is "borrow" the capacitor of my other oven (a 0.84 uF/1900V) and try it for a SHORT period. I'm a little reluctant at this, due to the sligtly inferior voltage rating (but I suspect it can't be hurt really if test is over a short period). For anyone asking gory details, my microwave oven is a Samsung type RE576TC produced in 1989. It is a 1050/600 W (absorbed/RF), is micro-controlled, uses magnetron Samsung 2M204-M3, a 0.91 uF/2100V capacitor and HVR-1X 3 diode. Thank you in advance for any hint. -- Here's where you can reach me (fixed-width font required). . ,-. . . . ,-. ,-. ,-. ,-. |- /,-.\ ,-. ,-. ,-| ,-. ,-. ,-. | | `-. |-' | | |-' | |,-|| | | -- |-' -- | | | | | | | `-^ `-' `-' ' ' `-' `' \`-^' `-| `-' `-^ :; `-' ' `-| `-- | ,| ` `' |
#4
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Advice needed for microwave diagnosis
On Tue, 9 Sep 2003 07:24:53 -0400, "Jerry G." wrote:
| Your address does not show properly to have a direct answer. Doesn't it mention the *fixed-width font* requirement, does it? Anyhow, direct answer is not an issue, when using Usenet. | Use something like for your address. This works well. It also works well for spambots! | You have to properly test the transformer, rectifier, and tube. You | cannot do this by visual observation. Sorry if I didn't made crystal clear I do possess and have used the equipment and knowledge to test most of it, except the HV part ;-((( | One or a few of these devices are at fault. Right, at least marginally for the moment. Thank you for your answer. (Umm, I guess this other .sig will make it much better in Outlook). -- You usenet can at reach q-e-d me dot here org |
#5
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Advice needed for microwave diagnosis
On 09 Sep 2003 08:07:33 -0400, Sam Goldwasser
wrote: | The HV diode and capacitor don't generally fail slightly. They are | either good or dead. Do you know which type (technology) those caps are? | Could be the magnetron. Difficult to test without swapping in a known good one | though. In this situation, would you go trying the known good 0.84 uF / 1900 V in place of the suspect 0.91 uF / 2100 V for, say, as long as one minute or two (e.g. 10 tests of 10 seconds each)? I believe it would be OK since there must be a large margin in the rating of these parts. I now think I can easily insert a small resistor in series with the HV transformer's primary, reducing the HV output. This will minimize the possibility of damage to the known good cap, yet produce enough HV to make it a real test. I'll try that and let the group know. -- Here's where you can reach me (fixed-width font required). . ,-. . .. . ,-. ,-. ,-. ,-. |- /,-.\ ,-. ,-. ,-| ,-. ,-. ,-. | | `-. |-' | | |-' | |,-|| | | -- |-' -- | | | | | | | `-^ `-' `-' ' ' `-' `' \`-^' `-| `-' `-^ :; `-' ' `-| `-- | ,| ` `' |
#6
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Advice needed for microwave diagnosis
On Tue, 9 Sep 2003 18:16:06 -0400, "Curmudgeon"
wrote: | Go he | http://www.repairfaq.org/REPAIR/F_mi...tml#MICFAQ_015 Thanks, but that's where I'm coming from ;-) -- Here's where you can reach me (fixed-width font required). . ,-. . .. . ,-. ,-. ,-. ,-. |- /,-.\ ,-. ,-. ,-| ,-. ,-. ,-. | | `-. |-' | | |-' | |,-|| | | -- |-' -- | | | | | | | `-^ `-' `-' ' ' `-' `' \`-^' `-| `-' `-^ :; `-' ' `-| `-- | ,| ` `' |
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