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My 1980s microwave died today. The light and timer circuit work

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Thread replies: 42
Thread images: 6

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My 1980s microwave died today. The light and timer circuit work but the magnetron and fan won't activate with the door closed.

Looking inside, the caps look fine, I don't see any obvious signs of short, the main 15A fuse is not broken. But I'm worried as frig farting around in there with high voltage circuits and caps I can't readily identify. I took pic related of the board behind the control panel, but this doesn't look like shorting, just discoloration from age or oil splatter or something. It's too large a spot to be from one or two burned components.

So maybe it's just the door switch or something. Maybe it's that top mosfet in pic related. What else should I look for? How long until the HV cap(s) have completely discharged?
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OP here, I should add that the magnetron stopped working while a cook operation was in process. It was humming along with 20 seconds to go when the magnetron shut off.
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Find the leads running from the board to the transformer. Put a clamp on amp meter there and see what you get when it's running.. if nothing then it's something in the 120 side like a fuse, door switch, relay on the board... or potentially the low voltage coil in the transformer is toast which you can check for by tediously checking continuity through all or in the case of the relay look for voltage coming from it when it's running... if you get amp draw then it's a problem in the high voltage side.. capacitor, diode, transformer, or magnetron... magnetron should have very low resistance between the two contacts and no circuit path to ground from either terminal... capacitor check for farads, the diode check with a 9 v battery to see if it's working.. transformer is continuity. Most microwaves these days leach capacitor to ground but if your paranoid bridge the contacts on the capacitor with a well insulated screwdriver or pliers after unplugging the unit.. take pictures of wires before disconnecting them.. more stuff in a microwave to stop it from running than lets it run... good luck
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>>1239034
Also worth mentioning that the high voltage cap is not on the board... post model # for more specific advice... also did it completely die or just stop heating?
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>>1239050
The interface and internal light still work, the timer can be started but the magnetron will not activate.

I found the most likely problem.

I checked all the switches and thermal fuses, all of them are fine except for this one. The physical mechanism inside the switch is broken, it rattles. Okay, so I'll replace the switch and that should be it.

However, while the lead running to it is not broken, it is singed. So what should I do about this lead? Should I snip it and re-crimp a new connector or just leave it and replace only the switch?
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And also, can I use any 15A normally open micro switch to replace this one or does it have to be 1/3 HP Kyung In too? I'm having trouble finding this exact one but I see a bunch of three prong NO/NC 1/2 HP Omron switches on eBay that look to be the same form factor.

Thanks fellas.
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>>1239085
the 1/2HP Omron will work just fine.
Check at digikey to see what the options are.
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>>1239078
>Should I snip it and re-crimp a new connector
yes, recrimp or solder the connector. it looks like it wasn't very good in the first place and stressed out components down the line. make sure you cut off the oxidized/heated part of the wire to get to good clean wire before attaching the new connector.
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>>1239200
>spade connector got charred
>just solder it, OP
definitely don't do that and better leave it as is
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>>1239333
explain
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>>1239335
the spade connector obviously gets heated due to high amps
soldering it will only lead to brittle soldier joint when this shit gets heated again and last thing you want is live magnetron wire (few thousand volts, btw) flapping inside a metal box

believe me, soldering the wire was easier and cheaper for the maker, but they intentionally put the connector there for a reason
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>>1239351
>few thousand volts
>picture of a 120 volt door switch
Anon you sound like you have no idea what you're talking about.
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>>1239359
then scratch that, i've read the thread diagonally

still, you don't want a live 120v wire to get disconnected and touch whatever inside
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>>1239085
You'd be fine with that. crimp a new shielded connector on... make sure the connectors on the new switch are the same size as the old or you'll end up putting all new connectors on to match anyway... fun fact in most microwaves depending on which switch fails it will either simply not heat, not heat and run cooling fan whenever the door is closed... or blow the 15 amp fuse when the door is opened or closed... first 2 aren't too bad... third scenario takes 2 fuses.... also consider replacing all three switches since you have it open and they're dirt cheap.. they've all had the same amount of wear...
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>>1239085
Also the cheapest version of these come with 3 prongs.. common, n/o, and n/c.. you can use these just either cut the prong you don't need off or put a shielded connector on it to cover it so you don't have live exposed metal..
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>>1239351
I agree with not soldering it, but the mag wires go nowhere near any door switches in any microwave I've ever worked on.. keep the high voltage side and the 110 side sepperate.
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>>1239034
Problem solved: $10 microwaves at goodwiil.

/thread
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>>1239078
I have a microwave that had a similar failure and I fixed it by recrimping a new connector to it.
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I got the new switch in and it's chooching away.

Thanks everybody.
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>>1240621
That's a bit of an anti climax. We need to know more of your incredible journey!!!!!
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>>1240621
Vintage wood looking metal... give it 10~15 years and that will be retro cool
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>>1240621
how does it works without the rotating plate in the botom?
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>>1241404
It's the antena that is turning, not the plate.
My grand parents have one like this, and it's great.
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>>1240621
We had same micro when I was a kid... looks like model from late 80s to early 90s.
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What's the main purpose of a microwave? Reheating leftovers?
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>>1239078
Confirm the fault before replacing.
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>>1240621
Good job.
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>>1241404
Most microwaves have a metal fan in the ceiling which spins in the path of the magnetron, reflecting cooking beams throughout the enclosure.

https://www.google.com/search?q=microwave+stirrer
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>>1241617
I wouldn't say most. Never actuality seen one that does that in person.
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>>1239034
then take out the magnetron and mount it on a cone shape mirror to make a death ray
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>>1239333
use high voltage/high temp solder and make sure the crimp is good
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>>1241702
find a way to turn it into a microwave based death furnace for making new age metallic death sculptures and such
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>>1241746
Hitler would shed manly tears if he saw your idea.
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>>1239570
This is diy and a $10 microwave wouldn't last 30+ years like op's
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>>1242006
10 of them would and it's not a big deal to have to live without a microwave until you have a spare half hour to get another
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>>1241019
Looks like it's not over yet...

There appears to have been a secondary casualty; this fan/pulley motor turns for half a second then stops. This motor is for the stirrer and the front cooling fan.

Here's a video.
>>>/wsg/1870369
The fan wiggles when cooking starts and when it stops, but won't spin. I can't start it by hand. Jiggling terminators doesn't do anything.

I apologize for this confusing diagram, it's a rat's nest in there, I'm no electrician and I'm kind of lost. Consider it a puzzle. But it seems that only the large white wire (supply from the LV side of the inverter) and the small beige wire (return to circuit board) are powering this fan, the blue and orange appear to be power distribution to other components. The rear cooling fan to which the orange wire is connected works perfectly.


Is the fan motor just bad? Replacements are basically nonexistent.
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Please find some way of testing the shielding, at least put a mobile in there and try and call it.
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>>1241404
Have you literally never seen a microwave without the turntable? My god.

When I was growing up, we had a fucking -wind up lazy susan- that was meant for microwaves. Turned it a few times to wind up the mechanism, and then let 'er rip.
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>>1242221
Not that same anon, but I'm 23 and have never seen that. Thank you for that info.
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>>1242177
Thanks for the splendid follow-up. I'm following every step of this. This is better than TV. Please keep us informed of all steps/findings etc
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>>1242039
Somebody doesn't understand /diy/
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>>1242221
Dude, that's a cool idea!
Thread posts: 42
Thread images: 6


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