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.

https://www.smcsustainability.org/climate-change/sustainability-academy/fixit-clinic/

 

[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-Ca...ave+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?

 

[justjunque]

Hey Alex.

It's a Model R-5H82.
Here's a crappy picture.

 

[combo52]

Reply 16 and 17

As usual chet you have no practical experience, automotive fuses are typically rated at 250 V, there is no surge of power when you turn on a microwave, plug it into your amp meter and watch. The current drawl goes up slowly it is nothing like a motor starting most electrical devices do not have a surge when they start lightbulbs, heating elements, etc. all draw less current the instant they start.

Microwave ovens, do not require special fuses, Toshiba microwaves, used plane, glass, fuses, for example.

I know of more than a dozen repair people who look at this site occasionally but very few will get involved and offer advice because of people like you chet, it’s obvious why you have to remain anonymous. You told me yourself that you often bullied and I can see why because you just spew out misinformation from behind your computer that doesn’t have anything to do with what’s been discussed.

 

[normadesmond]

WHOA!

WELL!

Seems there's been a flurry of opinion since I last checked in.

Sadly, I threw the old fuse away & the trash is out for pickup tomorrow so that's that. What I can say is the old fuse, though looking like a Buss fuse, was different in that the middle portion that is glass on the Buss may have been ceramic. I thought it was dirty after 40+ years. It was yellow-ish and not clear.

Now, for me, the problem is I don't understand much of what was written and am now confused. What will happen if I use the oven?

 

[Chetlaham]

<blockquote>
<span style="color: #ff0000;"><span style="color: #ffcc99;">As usual chet you have no practical experience, automotive fuses are typically rated at 250 V, </span></span>

</blockquote>
 

"Typically"

 

You don't assume. You read the product listing. While following the manufacturer's prescriptions.  I also stated that voltage isn't the only governing factor but in addition to short circuit interrupting current and applicable time current curves.

 

The goal is that the fuse blows without failing violently.

 

I have no doubt you've been installing none OEM fuses in microwave ovens for 50 years without penalty or knowing any better. But that doesn't mean its ever been OK. 

 

 

 

<blockquote>
there is no surge of power when you turn on a microwave, plug it into your amp meter and watch. The current drawl goes up slowly it is nothing like a motor starting most electrical devices do not have a surge when they start lightbulbs, heating elements, etc. all draw less current the instant they start.

 

 

</blockquote>
An amp meter averages its input data over a given period of time. An actual oscilloscope would capture upwards of 10x current draw for a few cycles that steadily decays with time, dropping down to the transformer's normal magnetizing + magnetron filament current current roughly 20 cycles latter. The current would would be at about 1 amp primary. At around 1.5 seconds the current would steadily yet rapidly begin to increase as the filament becomes hot enough to emit electrons eventually stabilizing around the microwaves normal input current. 

 

You are correct a magnetron gradually increases its intake of current if you choose to ignore a step up transformers inrush current. Why is inrush current important? Because inrush blows fuses and trips breakers when it brushes up or crosses an over current protective device's time current curve.  

 

Your line of denial based thinking has never boded well in the real world. Like the case where an engineer didn't take the full magnetizing inrush of various 45-250kva 480 to 208Y/120 volt step down transformers on on the essential electrical system in a hospital. Power goes out, emergency generator starts, ATSs begin transferring branches to and from emergency power. Magnetizing inrush of various dry type transformers on each floor exceeds the instantaneous settings on various 480 volt breakers tripping them leaving critical and life safety branches de-energized. ORs, ICU, emergency rooms, hospice beds and the like left in the dark. Code grey isn't something pretty nor would any engineer want to take blame for it. 

<blockquote>


Microwave ovens, do not require special fuses, Toshiba microwaves, used plane, glass, fuses, for example.

 

 

 

 

 

</blockquote>
There are many that do require special fuses, hence why manufacturers place ceramic fuses in a large percentage of microwave ovens. This is based on UL standards and engineering equations which take each ovens unique electrical characteristics into account. Fault current, let through current, conductor withstand, inrush, temperature, risk, ect, ect.

 

<blockquote>


I know of more than a dozen repair people who look at this site occasionally but very few will get involved and offer advice because of people like you chet, it’s obvious why you have to remain anonymous. You told me yourself that you often bullied and I can see why because you just spew out misinformation from behind your computer that doesn’t have anything to do with what’s been discussed.


 

</blockquote>
Of course you misinterpret my posts as misinformation not having anything to do with whats being discussed. That is a given when you have shown a protracted inability to grasp electrical theory. If you understood electrical theory you would understand why you can't just put any fuse in place of another.  

 

 

Funny you bring up me being mistreated. Have a look at (yet again) another Google review:

 

 

 

 

 

Slow down, listen and let people speak. Just because you read selectively (be it my posts on here or a someone's texts/email/letter) doesn't mean that holds true in reality.

[this post was last edited: 10/3/2023-00:18]

 

[Chetlaham]

@normadesmond

Honestly probably nothing. However if the fuse is ever called to blow from a bad door switch it may burst inside the oven. Doubt anyone would be injured, but may cause a small internal fire, damage around the vicinity of the fuse holder and to the oven wiring itself.

 

 

I did not mean to confuse. Point I'm trying to make is that if the oven previously had a ceramic fuse from the manufacturer, the new fuse should also be ceramic.

 

 

An OEM ceramic Whirlpool or GE fuse for $10 would suffice. 

 

 

 

[Chetlaham]

<blockquote>
"most electrical devices do not have a surge when they start lightbulbs, heating elements, etc. all draw less current the instant they start."

</blockquote>
 

<blockquote>
<span style="color: #ff9900;">"you just spew out misinformation from behind your computer"</span>

 

</blockquote>
A simple Google search literally says the opposite of what you said John, while vindicating what I said.

 

 

 

 

There is indeed a 15x surge of current according to Google.

 

Anyone can ohm out a cold 100 watt light bulb if they believe Google is inaccurate...

 

I normally don't address trivial semantics however I do not want other members to think I am spreading misinformation. That is not my the case. John you have a very power voice on here, many members take your word as incontestable truth, however this is not one of those cases. 

 

Can we at least agree on this?

 

[whitewhiskers]

On 10/1/2023 at 20:13 normadesmond wrote the following:

"...I'm electrically challenged..."

https://www.northjersey.com/story/n...lectrocuted-while-fixing-microwave/596748001/

 

[mark_wpduet]

It's staggering to think these things can last that long... and then when you think it's gone...it really isn't gone....

 

[normadesmond]

HA!

White Whiskers- Roz Chast knows my DNA. Intimately.

 

[kenwashesmonday]

Glass automotive fuses are generally rated for 32 volts.

 

[panasonicvac]

Reply #19

Very cool! I'm a huge fan of Sharp Carousels. I wish we had a Sharp or two in our house growing up, instead we have two Amana Radaranges (one has since been in storage). But we did however had a Sharp up at our last cabin, I wished we took it back home with us because it was my favorite.