REQUIEM FOR A MICROWAVE OVEN?

[normadesmond]

Hi-

Don't come around as often as I used to, but today's tragedy brings me back.

As you can see by the photo, this is my Quasar InstaMatic microwave oven. It holds terribly important memories for me. My long ago departed friend began teaching microwave cooking lessons when Quasar started making ovens. We hooked up just when this was starting for her, Summer 1979. Fast forward to 1988 when ovarian cancer took Marilyn. Her daughters gave me everything in her kitchen since they didn't need anything & I've been using that oven as my "daily driver" since then. Only time it ever let me down was when the light bulb FINALLY blew out. Being that I'm an electrical/technical imbecile I was pretty pleased with myself that I got the oven opened up & got a new bulb into it!

Tonight, as I pressed START the oven & the touch pad/clock went dark. Nothing.

No, it's not the outlet.

Even thought I'm electrically challenged I realize this oven is 44 years old, does anyone think there might be a way to repair it? It just kills me to throw it out.

Thank you!!!

 

[luxflairguy]

Saying a prayer! Long life!

 

[mattl]

Could be as simple as a fuse or a catadtropic failure.  There are high voltages involved  so care is needed if you open it up. 

 

Good luck, hope you get it running.

 

[rp2813]

Well Matthew,

I never thought I'd hear myself say this, but . . . that's a nice looking microwave!

 

I hope the problem is something simple and that needed parts are available.   There is a Fix-it Clinic program run by volunteers just up the peninsula (San Mateo County) where people can bring household items that need repair.  These are held at public libraries, schools, community centers, etc. and there is no charge for the work. 

 

Best case scenario would be having a similar program in your area that you could call to inquire whether they have logistics for accommodating microwaves.

Fixit Clinics - Sustainability Department - San Mateo County

Fixit Clinics are fun community-based workshops where neighbors, friends, and families work collectively to learn how to repair broken items.

www.smcsustainability.org

 

[hobbyapocalypse]

Yes I think it might be repairable

One day about 22 years ago my small Kenmore microwave went POOF when I hit the start button. I really doubted whether I could repair it, but I opened it up just to have a look, and noticed a broken wire. I reattached the wire and it's been doing fine ever since.

You might not want to tackle it by yourself but I hope it's as easy a fix as mine was.

 

[normadesmond]

Many thanks

Thanks for the replies! And thank you RP2813!

I never heard of Fix-it Clinics! Googled & found a few in the Twin Cities area in the near future. I have a feeling my oven is a bit on the big size (I will have to park & walk a decent distance to get to the church where the clinic is held & my oven is BIG and not light. I also have zero muscle left on my flimsy frame, so I'll need to figure this out.

 

[combo52]

Dead late 70s microwave oven

Hi Matthew, by far the most common problem when they suddenly go dead is a bad fuse is a little cartridge fuse much like cars used to use in fact, you could use a car fuse it’s usually 20 A.

Take the case off of it, and start tracing from the power cord you’ll see the fuse

Check and replace it if it’s open.

Other common problems are bad door switches, or the wires that attach to them.

I would say there’s a 90% chance that this is a reasonably easy fix

I started working on microwaves in the late 70s have worked on thousands

John L.

 

[normadesmond]

Another Great Suggestion!

Thank you John L!!!

I'll do exactly what you've written as soon as I finish my breakfast!!

 

[normadesmond]

HAPPY DAYS ARE HERE AGAIN!

BRACE YOURSELF FOR A "DEAR JOHN LETTER!"

John, I cannot express the happiness you've brought to me! Know what a mitzvah is? It is certainly what you did by reading my post and taking the time to answer! When I opened up the oven I found EXACTLY what you said I would! (something that rarely happens in life). As luck would have it, I have an old car & just happened to have a package of Buss fuses in the glove compartment! I didn't even have to go out!

THANK YOU.
THANK YOU.

THANK YOU!!

 

[panasonicvac]

Glad to hear it's working again! These Panasonic built Quasars are very fascinating units.

 

[rp2813]

Congratulations, Matthew!

 

I didn't know that Quasars were sourced from Panasonic.  This explains a lot.  I had a 1980 Panasonic that wouldn't quit, and it was as simple as crank-and-go to use.  It was still working fine when we left it behind after selling our house in 2008.  It was too big for the new kitchen or it would have come with us.

 

[normadesmond]

Matsushita!

Grew up with Panasonic stuff. Still have a TV from the 70s & a few different clock radios. Mum has a Panasonic hand mixer from the 70s & I made her swear she'll not throw it out.

Again, today was a great day. Thank you everybody! (and yes, I think my oven IS quite a looker)

 

[mattl]

Just curious, was it a clear fuse or was it coated with a white wrap?  The one time I replaced a fuse in a microwave decades ago it was a specialized fuse designed for MWs.  IIRC it was coated to prevent microwave energy from heating the metal in the fuse. the link shows a slow blow fuse designed for MWs and the initial high current draw that could blow a standard fuse.

https://www.amazon.com/Microwave-Cartridge-Slow-Blow-Compatible-WB27X10388/dp/B07LBGN7T9/ref=sr_1_3?keywords=microwave+oven+fuse&qid=1696273188&s=kitchen&sr=1-3

 

[combo52]

Working microwave yay

Glad you got it working there were many times back in the late 70s and 80s that I ran out of fuses and I went and took one of the fuses out of my dodge van and fixed it.

Microwave oven fuses are not slow blow. The ceramic fuses are not to keep microwaves away from the fuse, microwaves would go through ceramics. There is no microwave energy floating around inside the cabinet of a microwave where are the controls are.

Microwave ovens, do not cause a surge. When they start microwaving, they ramp up slowly if you listen to them it’s not like a motor starting.

But it’s not uncommon for a fuse just to get weak after many years and simply go, sometimes the monitor switch can also cause a microwave fuse to go. That’s why the fuses in there in the first place it’s to shut down the power to the microwave in case one of the two primary door switches sticks clothes for even a split second.

John L

 

[justjunque]

Yay!
I'm late to the party, or I was going to suggest/hope fuse a well.
The same thing happened to our 1991 Sharp Carousel recently, and it was a fuse.
So glad you're back up and running!

Barry

 

[mattl]

John, interesting.

 

I just replaced the fuse with what was originally in the oven.  It was an old Litton from the 70's. Just remember the guy at the appliance repair shop telling me there was something special about the fuse not to replace it with a standard fuse. That was my one and only experience fuse wise with a MW, had to be early '80s.

 

[Chetlaham]

A car fuse isn't always rated to interpret 120 volts potential at several thousand amps.  

 

There is literally a sticker next to the fuse holder that tells you the correct type.   

 

Microwave fuses are ceramic (with sand inside) because typical automotive glass fuses do not have the short circuit interrupting rating required for a household circuit. Microwave ovens work by short circuiting the line and neutral conductors headed to the step up transformer should a door interlock switch fail to break the circuit when the door is opened.

 

 

I recommend ordering the right fuse for the job:

 

 

https://www.repairclinic.com/PartDetail/Line-Fuse/3B74133Q/1267463

 

 

 

[Chetlaham]

Microwave Surge

All transformers have inrush, on average up to 10 times the rated full load current. Depending on the residual magnetism in the core (point in the sine wave when the transformer was switch off) relative to the the point in the sine wave the transformer is switch on, this current can be twice the average typical inrush. (20 times)  

 

1800 VA / 120 volts =  15 amps

 

15 x 20 = 300 amps

 

In reality the impedance (reactance and resistance) of the supply circuit will limit the magnitude of said inrush current, but regardless it will still be several times the Full Load Amps of the MOT for a cycle or two.

 

For this reason manufacturers recommend a specific fuse (time current curve) and rating for a microwave oven.

 

Second given that the available short circuit current at a household receptacle can be hundreds (typical) to thousands of amps (worse case) a fuse with a short circuit interrupting rating of 10ka (10,000 amps) is typically used by manufacturers. 

 

I sure hope there aren't thousands of microwave ovens with unsuitable fuses floating around in exitence.   

 

 

 

 

 

 

 

 

 

 

@mattl: you are 100% correct in everything you've said thus far minus there being microwave energy around the fuse holder. John is incorrect, microwaves do indeed have a current surge (just like any transformer or motor being started across the line) and require a special ceramic fuse both in handling current inrush AND thousands of amps of short circuit current should a door interlock get hung up.

 

Saying that any fuse will do is dangerous. I hate to say it but this thread has become like to many DIY threads on the internet where someone will tell the OP to do something like ("just run a lamp cord to your new outlet") and just because it works at face value ("hey, I can now charge my phone in here, thanks") everyone is praising the erroneous advice given and not the professionals saying ("Uh, lamp cord can't handle someone plugging in a space heater down the road and you've now got a none code compliant installation")    

[this post was last edited: 10/2/2023-16:58]

 

[panasonicvac]

Reply #14

Out of curiosity, what model is your Sharp Carousel or do you have pictures at least?