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Old 29th Apr 2021, 3:53 pm   #1
Lancs Lad
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Default 32 year old Sharp microwave oven...

My Sharp microwave (R-3A53(W)T) just stopped working the other day.

Bought new in 1989, and not the slightest problem ever since.

Until now...

I was heating up a mug of milk to make milky coffee when it made a 'growling' noise and then just stopped.

The clock display disappeared, and it was just dead.

So, I unplugged it and unscrewed the cabinet. And yes! I am very aware how dangerous the capacitor can be. As it turned out, the capacitor and it's electrical terminals are shielded by a difficult to remove metal cover, so no danger of touching them.

Just to be clear, the 'growling' wasn't a mechanical noise (so not the turntable motor) It was very definitely an 'electrical' noise! And, believe me, I DO know the difference!
The internal fuse had blown. The one that sits between the incoming power cable, and everything else.

I replaced it with some suitable fuse wire and plugged the appliance in. The clock display appeared fine, but as soon as I pressed start the fuse wire blew.

So, can anyone suggest what's wrong? The oven is spotless, so it's not anything to do with baked on food! I'm guessing either the magnetron, or maybe the capacitor. I'd really prefer to get it repaired, because it's so well made, and I've had decades of trouble-free use from it. It's even still got the original oven-light bulb from new!

I bought a new microwave yesterday (a 50 cheapie from Argos) but it's horribly tinny when closing the door, and just seems nasty and shoddy.

I only bought it as a stopgap until such time that I might get the Sharp repaired. I'm convinced it is repairable! I just need to find the right man (or woman) for the job.

Do people still repair microwave ovens these days?
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Last edited by Lancs Lad; 29th Apr 2021 at 4:15 pm.
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Old 29th Apr 2021, 4:01 pm   #2
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Default Re: 32 year old Sharp microwave oven...

The turntable motor is knackered. Maybe it's seized because of old grease.

It's almost certainly BER if you're going to pay a professional, even if parts are available. Everything had a finite life.
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Old 29th Apr 2021, 4:19 pm   #3
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Default Re: 32 year old Sharp microwave oven...

No, the turntable is fine - as I pointed out in my original post.

Maybe take the time to read it properly?

Just a polite suggestion.
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Old 29th Apr 2021, 4:41 pm   #4
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Default Re: 32 year old Sharp microwave oven...

I also doubt a stalled motor would blow the fuse, however if the motors windings have gone short it would emit an "electrical" growling noise during its demise.

Rewind time!
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Old 29th Apr 2021, 4:55 pm   #5
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Default Re: 32 year old Sharp microwave oven...

If it does turn out to be the magnetron let me know. I have a good one sitting around and i think it's a Sharp. Also have the capacitor..Yours for postage.

PS I think i would describe the noise i once got from an arcing magnetron as a growl.

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Last edited by The Philpott; 29th Apr 2021 at 5:10 pm. Reason: capacitor
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Old 29th Apr 2021, 4:55 pm   #6
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Default Re: 32 year old Sharp microwave oven...

A shorted capacitor is a good bet. Could also be the hv diode which you can’t test with a normal dvm etc as it’s effectively several diodes in series. As you know take care !

Ken
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Old 29th Apr 2021, 4:59 pm   #7
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Default Re: 32 year old Sharp microwave oven...

No, I'm convinced it's either the magnetron or the capacitor that's at fault.

I've heard that 'growling' before. Just once when I put a tub of butter inside to soften it, not realising that the tub had an outer covering of foil.

Maybe 'growling' wasn't the best descriptive word to choose?

How about 'arcing' or 'crackling'?
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Old 29th Apr 2021, 5:13 pm   #8
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Default Re: 32 year old Sharp microwave oven...

Thankyou, Dave, that's very kind of you.

I'll see what happens, and bear your offer in mind.
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Old 29th Apr 2021, 5:45 pm   #9
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Default Re: 32 year old Sharp microwave oven...

I had a Sharp of similar age and the cap was a bit low but the protection diode wired across it was short circuit. As the colour didn’t really go with our new kitchen I bought a new one and the noise from the transformer was diabolical. I’ve covered most of the thin tin cabinet with sound deadening materials and it’s now possible to have a conversation in the kitchen.
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Old 29th Apr 2021, 7:24 pm   #10
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Default Re: 32 year old Sharp microwave oven...

Quote:
Originally Posted by Lancs Lad View Post
Do people still repair microwave ovens these days?
I doubt it. Even if you could find someone it would probably be uneconomical due to cost of spares and labour....assuming suitable spares being available. The cost of microwaves has come down so much, it probably just isn't worth it. I don't even think you can get spares for them now like you used to unless you are an authorised dealer. I haven't seen anyone selling microwave spares for years. Last one I did was my old Goldstar about 15 years ago and I only got the spares because I knew the dealer!

I have a SilverCrest microwave with a grill from Lidl which is about five years old, faultless so far and does everything we need, gets a lot of use and cost 50 which was less than the one we had before which cost 70 and had fewer functions.....

I would bet the HV diode or the magnetron. If you can get into the magnetron cavity, make sure the HV capacitor is discharged before doing anything. You can remove the magnetron without too much difficulty and then you can check the waveguide. Sometimes they get contaminated and cause arcing so you might be lucky.

If you don't feel confident, don't even try to fix it yourself....these things can kill! I have seen someone thrown across a workshop after inadvertently touching the capacitor terminals with the unit not even switched on....he didn't discharge the capacitor. Fortunately he did survive but had a bad burn and a broken wrist where he hit the wall....
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Old 29th Apr 2021, 10:14 pm   #11
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Default Re: 32 year old Sharp microwave oven...

As mentioned in another thread, our even older (1986 I think) Sharp microwave stopped working last week, again with a blown internal fuse. I replaced the fuse and observed what appeared to be arcing in the waveguide. I took the waveguide end cover off, cleaned the gooey droplets (some sort of food condensate ?) out of it, cleaned the end cover then reassembled and tested. It's been fine ever since.

Cheers,

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Old 30th Apr 2021, 12:44 am   #12
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Default Re: 32 year old Sharp microwave oven...

Hi Peter.
The "growling" was probably the HV transformer responding to a short.

Yours has obviously blown the fuse in the primary side, but quite often they will sit there growling away for as long as the timer is set for because even when working normally, microwave transformers operate close to saturation, so they are difficult to protect by a fuse on the primary side.

A 1989 Sharp will almost certainly also have a long special fuse in on the HV side enclosed in a plastic tube and difficult to miss.

The short will be either (in order of likelyness) the HV diode, the HV capacitor, or the magnetron.

Don't even think about measuring the HV, I repaired hundreds of microwaves over a two year period and never had any need to do any testing other than cold resistance testing after unplugging and discharging the HV capacitor.
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Old 30th Apr 2021, 1:00 am   #13
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Default Re: 32 year old Sharp microwave oven...

While a 59,99 supermarket special won't usually be repaired, the more expensive microwave ovens such as this one, certainly are. Aswo carries most spares, or possible non-brand specific replacements for obsolete parts.
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Old 30th Apr 2021, 1:23 am   #14
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Default Re: 32 year old Sharp microwave oven...

Quote:
Originally Posted by Maarten View Post
While a 59,99 supermarket special won't usually be repaired, the more expensive microwave ovens such as this one, certainly are. Aswo carries most spares, or possible non-brand specific replacements for obsolete parts.
Shop the charity resale shops. They always seem to have older second hand ones. Maybe you can find one the same make as yours.
I see a few of those inexpensive, low power units. They sell them for $6.00 USD. Naturally, you know where they're made.
Dave, USradcoll1, trying to understand the way of today!
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Old 30th Apr 2021, 8:55 am   #15
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Default Re: 32 year old Sharp microwave oven...

The UK has quite tight liability laws applying to sellers of secondhand goods, and this has the effect of discouraging charities from selling electrical items, with some items (like microwaves) completely blacklisted. They just don't want the potential hassle. US thrift stores and UK charity shops are broadly comparable, but there are significant cultural and regulatory differences.

You sometimes find working microwaves dumped in skips (US:dumpsters) or on Freecycle/Freegle.

Back to the OP's Sharp please.
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Old 30th Apr 2021, 11:28 am   #16
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Default Re: 32 year old Sharp microwave oven...

I've also got an old Sharp microwave and it did something similar a few years ago and it turned out to be something arcing and tracking, so it was an easy fix once located. I can't remember exactly where the fault was as it was years ago, but you'll probably find the fault if you examine the innards closely. Other than that it may well be the diode - do some tests, but make sure there's no charge left in the capacitor before starting.

Regarding the turntable motor, it's usually me that sometimes doesn't read posts properly, but from what you say in your first post, the bit of fuse wire blew immediately on start up, so you had no chance of seeing whether the turntable started to rotate or not, so a shorted turn in the motor could still be a possibility, although I doubt it's the problem in this instance, but you can soon test it or disconnect it to prove yes or no.
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Old 30th Apr 2021, 11:54 am   #17
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Default Re: 32 year old Sharp microwave oven...

My (was parents') 1980s Sharp Carousel is on its second replacement magnetron.
I got it from magsells.co.uk and the previous one from CPC. The original had M4 studs, so M4 screws, nuts and shakeproof washers were needed.
It has a stainless steel cavity and has outlasted a few cheapies that rusted badly on the turntable track and the expensive Panasonic my parents replaced it with to go in the fitted kitchen!
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Old 30th Apr 2021, 9:06 pm   #18
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Default Re: 32 year old Sharp microwave oven...

I've managed to take a pic of the waveguide inside my oven.

Because it's on the ceiling of the cavity, it's not readily visible, so I've only just seen the brown mark.

A few questions, please:

What could the brown mark be, and what might have caused it?

And, is the waveguide easily removeable from inside the cavity? Are those plastic rivets just held in place by sort of sprung 'wings'? Will they just pop out if I gently prise the waveguide cover down with a carefully wielded screwdriver blade?

The interior was remarkably clean when I opened it up. No build-up of grease or grime on any of the electrical components. Understandably, the blades of the fan were a bit dusty, but after a perfunctory wipe, they're as good as new.

Thanks, by the way, for all your help and suggestions so far
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Old 30th Apr 2021, 9:19 pm   #19
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Default Re: 32 year old Sharp microwave oven...

The plastic rivets will just pull out, get your nails under them.

Richard
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Old 30th Apr 2021, 9:28 pm   #20
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Default Re: 32 year old Sharp microwave oven...

See GrimJosef reply #11
That's the waveguide cover, the mark is grease turned to conductive carbon and directly in the RF beam.

The cover made of mica. You can get it in generic sheets and cut it to size, but yours should be ok, just scrape the burnt area away with a screwdriver or finger-nail, the material is crystalline and stratified, so only the outer layer need be disturbed. You can probably do it in-situ.

I doubt this has fused your microwave though.
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