Broken GE Microwave Oven

The first time I posted about this, someone suggested it was just the fuse. And later I thought, it's dead, even the light doesn't turn on when you open the door, so the light is a clear indication it's the fuse. Good, although whatever's blowing the fuse might continue to blow them.

So this evening, after GE said they didn't want my old microwave back, I set about trying to fix it.

Instead of screws it had rivets holding on the case, but I noticed after I drilled the second one out, that it was a screw. But by this time I'd started drilling the other two and could no longer tell what the head looked like. But turned out there was a fifth on the side, and even though I couldn't see the "slot", it was there. It was a T-10, torx. I have tips for all these specialty screws and it was easier than drilling :-) So now I have to find replacements for the 4 I ruined.

As soon as the cover was off I found the fuse and could tell visually that it wasn't blown. Drat.

Later I saw an envelope taped inside and written on it was: "Do not remove envelope or destory (sic) contents. Replace contents in envelope."

Never seen that before. Long ago, with my Amana RadarRange Model 2, I had to beg the woman for a wiring diagram, convince her I wouldn't kill myself.

I like the word "destory". It's Chinese. Inside was a schematic, a parts location map, and a very detailed MWO Troubleshooting Flowchart, with 18 decison diamonds and at least two choices from each, so with 40 or more action boxes. (What is MWO?)

I immediately noted on the schematic two thermal cut-offs in series with the fuse , so I went back downstairs with a meter and in less than 4 minutes, I checked for residual (high) voltage, found none of course, and checked the cut-offs and found the problem. The second cut-off, the cavity thermal cut-off, tested open with a meter and even by looking one could tell it had partially melted on one contact and in the corresponding connector. There is even soot on the oven frame. Even though I had used the oven earlier the day it turned up broken and I hadn't gotten anything very hot. Hmmm. It's not in the oven cavity but the space where the other parts are. Could that have gotten hot?

I don't think so -- everything else looked pristine -- and I think this means the part was weak and once it's replaced, I won't have to look further for a problem.

Googling cavity thermal cutout, the first hit is from GE itself and looks almost like mine,

$9.80 plus $7 for 3-5 day shipping. They also offer 2- and 1-day shipping for $18 and 20.

But maybe I can do better. Googling C KSD201 110-0 I find one in Amazon. (Now I see that the one from GE is marked KSD301D 16A 125V 235C. Later I learned that 110 means 110^C so it's a good thing I didn't buy the one at GE.)

The thermal cutouts in Amazon cost between 6 and 13 dollars but first one tnat is meant to be used in GE is $48!!

OTOH, Amazon has 9 different ones from 9!!!! different makers or vendors labeled C KSD201 110-0 and they are $17 - 23.

Long story short, eBay had one with the exact appearance and embossed characters for 9.80 including shipping, and I ordered that. From N. Carolina, not far.

Now, if I want to use the $100 coupon, which I still think I deserve, yes?, I'll have two of them. I don't know anyone to give the other one to. Ugh.

I may not be an electronics expert but I do know English. You speculated "Could that have gotten hot?" and then decided, "I don't think so". You trouble-shoot and find an open thermal cut off with an apparent 110C protection value. Apparently something might have become hot enough to trigger the now always-open thermal cutoff you're replacing. Also, you've decided to replace it with a thermal cut off rated at 235C. In terms of temperature protection alone, not even considering a possible discrepancy in amperage rating (which you haven't provided for the blown cuff off) isn't going from a 110C to a 235C rated thermal cut off analogous to replacing a fuse rated 1 amp with a fuse rated 2 amps. So much for thermal protection. You might have well saved your $ and soldered in a short length of #18 copper wire. You've totally obviated the thermal protection the originally rated cut off was meant to provide. No?

I wonder if indeed there was an over-heating event that triggered the now defunct thermal cut off. Perhaps due to clogged air circulation vents from 2 years of condensed and/or spattered gunk that accumulated and at least partially blocked air flow? Does the ventilation fan motor rotate at full speed or is the rotor slowed down by gunk at the bearing(s)? Or, as you are apparently speculating, the defunct thermal cut off blew because it was probably under rated to begin with; a common phenomenon in inexpensive electronic circuits. However, more than doubling the thermal cut off temp is a substantial jump in specs.

I had an analogous situation with a medium priced stereo receiver. It repeatedly was blowing a fast blow instrument type fuse in the front end of the power supply circuit while the unit was in standby mode, many hours after last powered on use. It happened 3 times within a year. No evidence of any problems with any of the functions of the receiver after replacing the fuse to suggest additional damage to any circuit components but after a few months, the same fuse would blow again. No evidence of voltage surges as I use a surge protector and no other delicate electronics also plugged into the surge protector has had problems. And, no problems with any other home appliances not surge protected. Yes, the "protection active" light remains lit on the surge protector so I have no evidence of a surge protection failure. I forget the voltage rating but the repeatedly blowing fuse was rated at 0.5A. Finally, in desperation, I replaced the fuse with a fast blow instrument fuse rated at the same voltage but at a 0.6A rating. It's been 3 years now since doing that and no more blown power supply fuses and the receiver continues to function perfectly for all the inputs I use on it, e.g., digital coax, digital optical, analog, moving magnet phono input, and built-in AM/FM radio. Note however than I exceeded factory spec on that fuse only minimally, going from 0.5 to 0.6 amps.

In alt.home.repair, on Wed, 30 Oct 2024 09:49:59 -0400, Retirednoguilt snipped-for-privacy@fakeaddress.com wrote:

No, I looked at that first because some search term brought it up first, when I didn't know the 110 referred to temperature, but I wasn't going to buy it. Actually, although I don't like the ebay usually gives so little description, in this case, in the title of the ad, it said 110 degrees C.

You have a point. I did that "the last time", a few years ago. A friend had moved from Baltimore to Europe shipping her big screen tv with her. When unpacking a helpful neighbor brought a plug adapter and plugged her tv in, with 220V. Later he said he didn't know anything about tvs or maybe it was electricity. When I came to visit the glass fuse inside was blown and I didnt' have another fuse, but when I travel do carry some tools, a meter, a flat and philips head screwdriver, and a couple jumper wires, with alligator clips on each end. (sold in packages of 10. I used to carry a tape measure, that actually enabled me to help a cute girl in a hardware store. I connected BOTH jumper wires across the fuse holder, plugged the set into a 220 to 110 transformer, and poof, a cloud of smoke. Insulation on both wires had melted and wires broke. After that I found the power supply circuit board on Ebay, for sale in Baltimore of all places, and we got a friend of my friend who lives in Baltimore to pick it up and bring it when she visited, so I'd be sure to get it before my trip was over. It was $42 and it fixed her tv. But this time I didn't think to jump it. The rest of the interior looked perfect and I don't believe I ran it long enough to overheat, even if there is something else wrong. And the thermal fuses I'm used to don't melt when they blow. You can't efven tell they're blown without a meter. Of course those are mostly in hair dryers, not microwaves.

Also, I'm not sure if I'd have to put the cover on to test it. I would think not, that the microwaves are trapped if you don't mess with that part, but maybe not.

Here is the part.

You've

Didn't use it much and much less for things that bubble. IOW, no clogs.

No gunk, spins nicely after I flick it, but I haven't tried to power it.

No, no. I bought the same thing.

AT any rate we'll see in a few days when the part comes.

The right move, nonetheless.

It looks like they were very cautious and chose the minimum value that would work, but in your case it was too minimum, so to speak. LOL

My guess is that MWO is "Microwave Oven".

LOL By golly, I think you're right! You need to spell things out for me.

Further reading of the documentation inside the MW agrees with you.

In the flow chart, it asks if the fuse is ok, an dif not it says "Install service breaker across fuse holder." I'm not convinced most repairmen would do this, instead of just another fuse, but nonetheless, that's the recommendation. I have saved resettable circuit breakers from some devices, for something like this, but I've never used one. It's not like I'm fixing things every day or even every month.

And further in the flowchart it "agrees" with me. That is, it has one measure the voltage at a specific place, then "Check thermal cut-out(s), and if one is open, it says Replace TCO. So that's what I'm doing.

So it agres with both of us. ;-)

%Also, I'm not sure if I'd have to put the cover on to test it. I would %think not, that the microwaves are trapped if you don't mess with that %part, but maybe not.

And the docs cover that too, indirectly, by only warning about the high voltage when the cover is off, not microwaves just because the cover is off.

In bold and all caps, it says TO PREVENT ELECRTRIAL SHOCK USE EXTREME CAUTION WHEN DIAGONOSING OVEN WITH OUTER CASE REMOVED AND POWER "ON'. THEN [THE] HIGH VOLTAGE SECTION OF THEE POWER SUPPLY, INCLUDING OF LEADS, IS 4000 VOLTS POTENTIONW ITH RESPECT TO GROUND.

So clearly they expect diagnosing with the cover off.

It does say "When replacing the Magnetron, be certan the R.F. Gasket is in place and mounting screws are tightened securely to wave guide. Failure to do so can result in hazardous levels of microwave leaking. permform microwave leakage test." And at least two places it says THE MAXIMUM LEAKAGE IS 4 mw/cm2.

In another place it says the maxiumum is 5 mw/cm2. "4 mw/cm2 is used to allow for measurement and meter accuracy." !!!

I have a microwave meter, bought from Radio Shack when I had a RadarRange that had no door latches, only a spring. It's 40 years old now but I'm sure it's still good. I've used it with other used mw's. It doesn't have numbers, only green, yellow and red.

The documentation is very good. Is it required by American law, or GE, or can we credit the Chinese manufacturer for including it?

Lots of things I haven't included like the 3 door latch switches (US rule, must have 3.), warnilng about discharging capacitor before touching. ""Under normal operation the capacitor should fully discharge within 30 seconds." But who is normal these days? Also, How to test the interlock system, hw to adjust it.

My biggest complaint about this was that I can't hear the timer beep, even when the tv is barely on. I have half a dozen piezo eletric beepers I've removed from broken stuff, some much bigger than what is in there now. Now would be the time to replace the oen that's in there, but I'm going to skip that.

Oh, yeah, here is what it says about the troublesome sensor. "Oven temp sensor (flame sensor) An oven temp sensor is mounted on the oven cavity at the right side. It's purpose is to automatically shut off the oven in case he cavity overheats for any reason. The thermostat will open at 230^F(110^C) and is non-resetable. The device is connected to the line side." Oven cavity must refer to the utility space, not the space for the food. There is NO WAY it was ever 230^F in there. All the insulation whould have melted, instead of just 1/8" of the connector. There would be other signs of heat.

The fact that they sell so many of these at retail, eBay, Amazon, elswhere from so many manufactrers means to me that they must fail a lot in appliances that are not junked afterwards. If you don't have a wiring diagram, you could easily not realize that it's in the main power wire, in series with the fuse. In this microwave, there is also the magnetron thermal cutout, which I'm sure can also fail.