Advice needed on microwave repair

[John Howard]

My microwave began randomly powering itself off while running and then stopped powering back on altogether. When I took the cover off I found that one of the wires leading to the thermal fuse had melted. Is this something that can happen just when the thermal fuse fails, or is it a sign there is another problem with the microwave? 

[Ben Eells]

Probably the fuse. I'm planning on bringing some microwave parts to LVL1 on Tuesday to donate to the boneyard. I think I have a fuse.

On Jan 14, 2018 4:51 PM, "John Howard" <cyrnu...@gmail.com> wrote:

My microwave began randomly powering itself off while running and then stopped powering back on altogether. When I took the cover off I found that one of the wires leading to the thermal fuse had melted. Is this something that can happen just when the thermal fuse fails, or is it a sign there is another problem with the microwave? 

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[John Howard]

I did a continuity test on  the fuse that was in line and it works. Another thing I noticed was the connector on the burned side of the thermal fuse is loose on the fuse and continuity is intermittent as a wiggle the connector.

Im still well on the amateur side of electronics however I'm inclined to think that each time the microwave has powered itself off there was a short at that connector that melted the wire a little more. If this is a feasible theory then I think I can just order a new thermal fuse scavenge the boneyard microwaves for a similar connector and replace the parts.

Does all of that sound like the most reasonable plan? 

[Ben Eells]

That's a likely scenario. The fuse may still be good in which case all you need to do is replace the wire/connector.

[Chris Hettinger]

No short, sounds like a loose connection that has gone high resistance. I agree with Ben. If micro has been working, then fuse is still good.

[David Ortiz-Grob]

Sounds a lot like the problem charles fixed on a visitor's TV. Either new connector  or direct solder 

[2600]

Looks to me like a clear-cut case of the "CC Blues". CC, as in cruddy connection. The connector clip that slides onto the temp switch's flat tabs is a type famous for coming loose. When it does, the amount of metal surface that carries the current is reduced. Creates a resistor at this spot. Current through this unsolicited resistor gets turned into heat. This oxidizes the metal surface of the clip and the flat tabs both. Raises the resistance higher, releases yet MORE heat, and you have a downhill-snowball effect. Eventually the resistance of the connection gets high enough to shut it all down. 

Losing the slide-on lugs is the quick answer, if you can clean the tabs shiny enough to accept solder. Solder won't adhere to crusty oxide-coated metal. 

The long answer is new lugs and a new temperature-shutdown switch. I don't recommend simply "jumping" across it with a piece of wire. Disabling safety features is for Crazy Russian (Ukranian) YouTube kids from Luhansk. And generally a bad idea for the rest of us. 

Just be sure you have a solid solder connection from each wire to its tab. 

Should work.

On Monday, January 15, 2018 at 1:26:36 PM UTC-5, David Ortiz-Grob wrote:

Sounds a lot like the problem charles fixed on a visitor's TV. Either new connector  or direct solder 

On Sun, Jan 14, 2018 at 5:41 PM, Chris Hettinger <christophe...@gmail.com> wrote:

No short, sounds like a loose connection that has gone high resistance. I agree with Ben. If micro has been working, then fuse is still good.

On Jan 14, 2018 17:31, "Ben Eells" <comfort...@gmail.com> wrote:

That's a likely scenario. The fuse may still be good in which case all you need to do is replace the wire/connector.

On Sun, Jan 14, 2018 at 5:28 PM, John Howard <cyrnu...@gmail.com> wrote:

I did a continuity test on  the fuse that was in line and it works. Another thing I noticed was the connector on the burned side of the thermal fuse is loose on the fuse and continuity is intermittent as a wiggle the connector.

Im still well on the amateur side of electronics however I'm inclined to think that each time the microwave has powered itself off there was a short at that connector that melted the wire a little more. If this is a feasible theory then I think I can just order a new thermal fuse scavenge the boneyard microwaves for a similar connector and replace the parts.

Does all of that sound like the most reasonable plan? 

On Jan 14, 2018 4:56 PM, "Ben Eells" <comfort...@gmail.com> wrote:

Probably the fuse. I'm planning on bringing some microwave parts to LVL1 on Tuesday to donate to the boneyard. I think I have a fuse.

On Jan 14, 2018 4:51 PM, "John Howard" <cyrnu...@gmail.com> wrote:

My microwave began randomly powering itself off while running and then stopped powering back on altogether. When I took the cover off I found that one of the wires leading to the thermal fuse had melted. Is this something that can happen just when the thermal fuse fails, or is it a sign there is another problem with the microwave? 

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[John Howard]

Thanks for that explanation. And yes once I got the melted plastic off the connector clip was quite loose. Also the flat tab on that side is loose on the temp switch too. So I was never considering still using it. 

Online I have found the part for $10 to $15 so I'm going to order one and Solder the wire on that side to the new one and wrap it in heat shrink tubing. 

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[David Ortiz-Grob]

before you spend $10, flux and sand the shit out of it and try soldering

[Matt B.]

^ what David said

[John Howard]

I'll take another look, I didn't look close enough to see if the arm was held on by a rivet or tiny screw. If I can get that off clean it up and reattach then I'll go with it. Otherwise I'll order one. 

On Jan 16, 2018 12:01 PM, "David Ortiz-Grob" <david.or...@gmail.com> wrote:

[David Ortiz-Grob]

I don't follow. you shouldn't need to remove anything but the wire and a knife + some hand sandpaper should be enough to get it clean enough to solder. 

[John Howard]

It wasn't just the wire that was loose. The tab itself was loose in its connection to the body of the device. After closer inspection since my last email on it. The post that attaches the tab to the device was loose somewhere inside it. I've already ordered a replacement because of that. 

[Ben Hibben]

Thanks for keeping us updated!!

Blenster

ᐧ

[David Ortiz-Grob]

F

[2600]

The flat brass connector tabs are held to the body of the thermal switch each with a rivet, usually also made from brass. High temperatures will cause the rivet to loosen. No good solution but to replace the thermal switch.