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ApplianceGuru.com: The Samurai Appliance Repair Forums > Do-It-Yourself Appliance Repair Help > The Kitchen Appliance Repair Forum > GE Microwave blows fuses |
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| GE Microwave blows fuses | Rate Topic |
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| Posted: Tue Sep 20th, 2005 04:36 am |
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1st Post |
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thetone Grasshopper
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 Our combo Oven/Microwave is about 20 years old and today blew a fuse for the first time (the microwave part). It's a GE (yeah, I know) model JKP60G*02. I replaced the fuse with a 15 A 250V ceramic ABC type and it ran OK for a while. I verified that the fan was working. Later it blew again while nuking dinner. Does this suggest a specific faulty component or just the beginning of a diagnostic nightmare (or a hunt for a new microwave)?
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| Posted: Tue Sep 20th, 2005 04:51 am |
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2nd Post |
Jedi Appliance Guy
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The force is saying "PCM" (Power Control Module). Could also be a loose fuse holder. If it blows right away check the high voltage capacitor. Read the tech sheet. Its not far from where you found the fuse.Some parts on that machine are NLA. I wouldn't spend big money fixing it.
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| Posted: Wed Sep 28th, 2005 08:35 pm |
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3rd Post |
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thetone Grasshopper
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 Follow-up: After limping along through two more fuses, I realized that the unit would have to be taken out and disassembled. I discharged the capacitor and uncoupled the various wire group connectors to take the control board out. In the process I noticed that one of the wires (brown) going into a connector had a black discoloration within the connector. I pulled both ends of this wire out of the connector and found with the ohmmeter that the continuity at this point was intermittent and could be broken by pushing and pulling on the junction of the wire and the male end of the connector. I put in a set of single connectors on that wire to run outside the group connector, put in a new fuse and reassembled the connectors. So far, it’s working.
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| Posted: Sun Oct 2nd, 2005 03:36 am |
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4th Post |
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thetone Grasshopper
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More follow-up: After a day or so it blew another fuse. I checked all the wiring and the control board. Everything looked fine. I re-soldered the fuse holder just for completeness, but it didn't help. Since this is an oven/microwave combo unit and I don't want to have to replace it, I have ordered a new control board.
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| Posted: Fri Oct 21st, 2005 11:34 pm |
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5th Post |
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thetone Grasshopper
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Bought new control board from Repairclinic.com and installed it. Miked a mug of water for 3 minutes and then 30 seconds more until boiling. About 4 hours later I tried to mike a couple of hot dogs and it blew the fuse within one second of starting. Suggestions?
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| Posted: Mon Oct 24th, 2005 05:14 am |
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6th Post |
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Moostafa The Ayatollah of Appliantology 
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Hello, my fuse-blowing friend. I seems to me that there is a problem with one of the high voltage components. The magnetron may have developed a high resistance path to ground, or perhaps the varnish insulation on the primary winding of the HV transformer has gotten too hot in places and it leaking current to chassis ground. As Allah is my guide, I would begin my investigation there.
____________________ Allahu Akbar! Moostafa |
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| Posted: Wed Oct 26th, 2005 11:06 pm |
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7th Post |
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thetone Grasshopper
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 Grasshopper is puzzled and has come up empty-handed in his high voltage search. The high voltage transformer shows normal resistance values - primary coil 0 ohms, step down coil 0 ohms, secondary coil 2 ohms, high voltage tap to ground 73 ohms, and infinite resistance between ground and primary and step-down coils. Magnetron leads show infinite resistance to ground. The high voltage capacitor shows a slight swing with an analog meter, then infinite resistance, and ditto when probes reversed. Capacitor was tested in another microwave and seemed to work fine. Ideas?
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| Posted: Wed Oct 26th, 2005 11:40 pm |
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8th Post |
Ron
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thetone, have you checked your door switches, if one of these switches good bad, it will take out that fuse, this can happen intermittantly as well,...Ron
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| Posted: Thu Oct 27th, 2005 01:25 am |
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9th Post |
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thetone Grasshopper
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This model has three door switches: primary (bottom), K2 relay (middle), and secondary (top). My results: Primary: closed 13 ohms (should be 0); open 22 (should be "some ohms") K2 relay: closed 207 (should be "some"); open 0 (should be 0) Secondary: closed 1-12 variable (should be 0); open infinite (should be infinite) Primary and secondary switches may be questionable. What do you think?
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| Posted: Thu Oct 27th, 2005 01:41 am |
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10th Post |
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thetone Grasshopper
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Correction: The K2 relay is part of the secondary switch. The middle switch is the monitor switch.
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| Posted: Thu Oct 27th, 2005 02:03 am |
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11th Post |
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Trying to help Fellow, Academy of Sublime Masters of Appliantology 
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Door switches when good should either read ZERO ohms between the contacts that should be closed, just like you put your meter leads together, and completely open between the open contacts like your meter was just sitting on the table with the leads in your pocket. Some switches are normally open like your primary and secondary, some monitor switches are normally closed. Make sure you mark what switch goes where an either look at the schematic to see what type of switch it is, or read it right off the switch. I like to prove which switch it is to verify the problem, but I have always changed them as the set. The readings you list on the primary are very suspect. Do you have a schematic you can scan in so we can look at it? Blowing fuses are synonymous with door switches sticking.
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| Posted: Thu Oct 27th, 2005 02:20 am |
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12th Post |
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Pegi Fellow, Academy of Sublime Masters of Appliantology 
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From a Maytag service bulletin: unit blows the house breaker or opens the cavity fuse at start up. Interlock Monitor Switch does not operate properly. Replace the monitor switch and the cavity fuse if it is open. I understand yours is G.E. but the same problem night be unique to all brands?
____________________ To ask a question, use our new forums==> http://appliantology.org 365-Day No-Hassle Return Policy at RepairClinic! 
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| Posted: Thu Oct 27th, 2005 03:33 am |
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13th Post |
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thetone Grasshopper
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Schematic submitted as attachment (JPG). Attachment: GEMicrowave.jpg (Downloaded 11 times)
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| Posted: Thu Oct 27th, 2005 08:23 pm |
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14th Post |
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thetone Grasshopper
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The above resistance values are not for isolated switches, but are checkpoints in the circuit as given by the tech sheets. The primary switch measurements turn out to be 0 and 22 ohms, because I discovered I was at the wrong checkpoint on that measurement. I took out primary, secondary, and monitor switches and checked them out and they seem to be working perfectly. I cleaned up the contacts and blew a little TV tuner cleaner/lube through the latch switches (WB24X5168 microswitches) and put everything back together. Checkpoint readings are as they should be now and a preliminary check of the microwave shows it running OK. I'm not terribly confident that I've solved the problem. Time will tell. If there are any other things that could cause fuse blowing that we haven't covered, feel free to add.
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| Posted: Mon Nov 7th, 2005 04:59 pm |
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15th Post |
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thetone Grasshopper
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Well, it's been 11 days with no more blown fuses. It is very doubtful that the major systems are at fault. It seems that the door switches were the problem, since they were the only components that I actually did anything to (clean/lube). Thanks for all the help, appliance guys!
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| Posted: Sun Nov 13th, 2005 01:38 am |
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16th Post |
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thetone Grasshopper
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After 16 glorious days my microwave blew another fuse. But this time it gave a clue. I had heated a mug of water for 3 minutes. Then I heated it for 30 seconds more to make it boil. As the 30 seconds was nearing an end, the sound changed. The normal fan sound became kind of fluttery and "sick" sounding, then the fuse blew. Is it trying to tell me something?
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| Posted: Sat Nov 19th, 2005 05:38 am |
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17th Post |
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thetone Grasshopper
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OK, here's the latest in this saga. The fuse blowing is definitely accompanied by a change in the sound. Just before the fuse blows (usually after more than 30 seconds of operation), the normal fan sound changes to a slightly louder, deeper and "fluttery" sound. If I stand close to the microwave and push "Clear" as soon as I hear that sound, the fuse won't blow (delayed MDA type fuse). I can then start it again and it will be OK for at least 30 seconds, sometimes much longer. I'm starting to doubt if the door switches are the problem. It sounds more like some component is "breaking down" during operation. Does what I've described ring a bell with anyone?
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| Posted: Thu Nov 24th, 2005 04:11 pm |
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18th Post |
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thetone Grasshopper
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Well, this problem seems to have left everyone scratching their heads. It's intermittent (always a P.I.T.A.) and a check of the usual suspects has turned up nothing. I've decided that when I replace this unit, it will be with separate components, NOT a combo unit. Until that time comes or until some part finally quits for good and allows me to replace it, I have wired in a fuse-type circuit breaker just behind the vent louvers. When it blows, I just use a piece of wire to push the reset button and we go merrily on. If I ever find the real problem, I'll post it, otherwise consider this case closed.
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