Fixing a Microwave...?

[h2sammo]

Is it hard to fix a microwave?

I bought this huge 2 cubic feet 1200W Kenmore Microwave from ebay. I got it very cheap (7 bucks). It looks gorgeaus, like its been never used, everything works, the programming, the times, etc, its just that it does not heat anything.

I cold take it to Sears, I guess and fix it there, but I wonder how much they would charge me for it. What do you guys think, could i fix it myself? Any of you know how i would go about it?

Thx

 

[WW]

search around in google, there are several repair faqs for electronics online

here's one

be careful...microwaves have high voltages (around 4kv ), and can kill you pretty easily.

the problem with fixing microwaves is getting the right replacement parts. And if it's the magnetron, that is probably around $80 to replace.

good luck

 

[WombatWoman]

This looks useful.

Used microwave ovens are so absurdly cheap, however, that I really can't see spending the time to tinker with one unless you are just desperate for something to tinker with. I got a nice working microwave at a garage sale for $15.

 

[Jerboy]

Originally posted by: h2sammo
Is it hard to fix a microwave?

I bought this huge 2 cubic feet 1200W Kenmore Microwave from ebay. I got it very cheap (7 bucks). It looks gorgeaus, like its been never used, everything works, the programming, the times, etc, its just that it does not heat anything.

I cold take it to Sears, I guess and fix it there, but I wonder how much they would charge me for it. What do you guys think, could i fix it myself? Any of you know how i would go about it?

Thx

Assuming it isn't an inverter microwave, take it apart and disconnect the input to high voltage transformer. Put something in the oven, close the door and apply 120V on high voltage transformer. Check to see if it heats.

If not, you could have: defective HV transformer, magnetron, HV capacitor, or HV rectifier(sometimes integrated into cap). That's pretty much all you need to get the microwave working and all, except for HV rectifier(a few bucks) are VERY expensive. On inverter microwaves, there is a possibility of faulty inverter.

 

[h2sammo]

When you say "very expensive" you guys scare me.
How much can a magnetron be? $20, $50? it cant be more, can it.
Does anybody know how much the sears guys charge?

thx for the linkies

 

[Monel Funkawitz]

Ok. Here is my $0.02

99% of the time, a microwave oven that will not heat is due to a blown fuse in the safety interlock circuit or defective relay. Microwave ovens are designed so if you try to open the door with the magnetron engaged (For example, the relay sticks closed), a doorswitch will crowbar, and pop the fuse. That is why there is three door switches if you look really closely. Two are used to stop the timing circuit, and the third is a fail safe door monitoring circuit to pop the fuse.

BEFORE YOU DO ANYTHING, SHORT OUT THE HIGH VOLTAGE CAPACITOR WITH A WELL INSULATED SCREWDRIVER!! Sometimes the bleeder resistor will fail. Touching that cap charged is instant death. Remember, the output from that HV transformer will KILL you by itself. No questions asked. 2,100 volts at 1 amp = dead h2sammo. You will be a human candle. Add the capacitor, and it is 10 times worse.

Now to the good stuff. Check the fuse, because some of the kenmores used it after the timing circuit, rather than off of the supply line. After that, check the magnetron energising relay to make sure the output is triggered. Sometimes these fail open. Next, unplug it, discharge the cap, and pull the cover inside the cooking cavity that covers the magnetron. Look for black marks. If there is, try it without the cover and see if it heats. If it does, the cover carbon arced, and shorted it out. If not, discharge the cap again, and check the HV diode with a meter. I use a HV tester I made for a negative ion generator on these. It kicks out about 10kv, 20khz, and about .0000000000001 milliamp . Real low. I hold the HVdiode close to my finger, and see if it sparks when the lead is brought close to the terminal, if it does, I reverse it, and it should not. it finds faults that the ohm meter won't, but a regular meter will work plenty well. If that isn't the problem, then the magnetron is dead (Which happens to a good part of new ones. Magnetrons are REALLY touchy, and usually fail within the first two minutes of operation. 99% of the time the heater burns out. Alot of current here! ) Magnetrons are anywhere from $30 to $200+

You can fix it, but BE CAREFUL. I've almost bought the farm a couple of times from these damn things.

 

[Lvis]

Monel is right.

Many times you can fix them with just a fuse. All it took for mine was a trip to the hardware store, and some spare change.

 

[NetworkDad]

If you've got a real cheap microwave, it might be better just to go pick up a new model.

 

[dude]

2,100 volts at 1 amp = dead h2sammo

I don't believe him. Try touching it and report back to us! If you're still alive!

 

[h2sammo]

OK dude

Monel Funkavitz is right.

I tried it, and indeed, 2,100 volts at 1 amp = dead h2sammo

im dead, arrrrrrrrgh, and black fried

 

[Jerboy]

99% of the time, a microwave oven that will not heat is due to a blown fuse in the safety interlock circuit or defective relay. Microwave ovens are designed so if you try to open the door with the magnetron engaged (For example, the relay sticks closed), a doorswitch will crowbar, and pop the fuse. That is why there is three door switches if you look really closely. Two are used to stop the timing circuit, and the third is a fail safe door monitoring circuit to pop the fuse.

The test procedure I suggested, which was disconnecting everything and feeding the HV transformer directly with 120V is adequate for testing the integrity of RF transducer and its high voltage power supply. Microwave interlock works in a unique way. When the door is open, it actually shorts across the high voltage transformer. When one door latch comes in contact with the switch, it opens the short and second latch applies power. If the second latch fails, it simply won't get power. If the first latch fails, it shorts out the power and blows the fuse. 99% of latch malfuctions can be attributed to door misalignment. Door misalignment can mean RF leakage.

BEFORE YOU DO ANYTHING, SHORT OUT THE HIGH VOLTAGE CAPACITOR WITH A WELL INSULATED SCREWDRIVER!! Sometimes the bleeder resistor will fail. Touching that cap charged is instant death. Remember, the output from that HV transformer will KILL you by itself. No questions asked. 2,100 volts at 1 amp = dead h2sammo. You will be a human candle. Add the capacitor, and it is 10 times worse.

I use my soldering iron. I discharge the voltage into soldering iron. It saves me from loud *BANG*.

Now to the good stuff. Check the fuse, because some of the kenmores used it after the timing circuit, rather than off of the supply line. After that, check the magnetron energising relay to make sure the output is triggered. Sometimes these fail open. Next, unplug it, discharge the cap, and pull the cover inside the cooking cavity that covers the magnetron. Look for black marks. If there is, try it without the cover and see if it heats. If it does, the cover carbon arced, and shorted it out. If not, discharge the cap again, and check the HV diode with a meter. I use a HV tester I made for a negative ion generator on these. It kicks out about 10kv, 20khz, and about .0000000000001 milliamp . Real low. I hold the HVdiode close to my finger, and see if it sparks when the lead is brought close to the terminal, if it does, I reverse it, and it should not. it finds faults that the ohm meter won't, but a regular meter will work plenty well. If that isn't the problem, then the magnetron is dead (Which happens to a good part of new ones. Magnetrons are REALLY touchy, and usually fail within the first two minutes of operation. 99% of the time the heater burns out. Alot of current here! ) Magnetrons are anywhere from $30 to $200+

You can fix it, but BE CAREFUL. I've almost bought the farm a couple of times from these damn things.

Save all the testing until you have applied 120V directly at the transformer. If there is a hard short, you'll simply blow the fuse/breaker at the breaker box. Say bye bye to microwave oven if you couldn't activate it by applying 120V at transformer and problem isn't diode.

Magnetron and HV transformers are usually $50+ each.