Sharp R959SLMAA combination oven dead or not?

[T5 TDI]

I just wondered if anyone has any tips before I replace this oven. It is around 8 years old and it's as if the lights are on but nobody is home!

Absolutely everything works as normal, the turntable turns and the display and all its functions act normally but there is no heat from the oven, grill or microwave. I have also tried it on every other setting (autocook, combination etc) but apart from the fan and the turntable going round nothing happens, it just pretends to cook! I have tried unplugging it for an hour but it's the same.

There isn't an internal fuse or some kind of reset I could try is there?

Thanks in hope because the poor old thing is fine otherwise and I hate just chucking stuff out if it can still be given the kiss of life!

 

[jj4091]

Not familiar with that appliance but for 3 different heat sources to not work it would appear to be a common internal supply problem. My guess would be you have a burnt neutral connection somewhere. You need to check the wiring visually in the first instance & then start checking voltages with a multimeter.

 

[T5 TDI]

Thanks for your reply. I've got the cover off now (and capacitor discharged!) And this looks like it could have caused the problem.

I've cleaned the top part of the grille just for comparison. I wondered about the thermal cut outs. The manual I downloaded says there are three. I think the two of them (the 170 degrees ones for the oven and grill) will reset themselves but the third (125 degrees) thermal cut out says it is not resettable. It seems to say it will probably be caused by the magnetron overheating. I would test it if I could find it! The other thing that seems odd is that I have lost all three sources of heat as you say. I haven't spotted any melted connections so far.

I tested both these fuses on the PCB.

Here is a pic of the internals. Can you could spot the thermal cut for me just so I can eliminate it given that blocked grille..

 

[SFK]

T5,
This is what an oven thermal cutout or thermal limiter can look like. Two connectors and a flat thermal plate to be screwed flat to another metal plate .
https://www.espares.co.uk/search?SearchTerm=Sharp thermal
or
https://www.google.co.uk/search?cli...1j0i13i30k1j0i13i5i30k1.0.JIjLN6aB1wY#imgrc=_

Is that not the thermal cutout dead center of the above image. It looks correct as it has relatively thick wires and the Live (red) going in and live (red) then going out again, and is bolted to the metal plate?

If it is I would test it by pulling off one of the wire connections, and using a multimeter across the connections testing for Continuity or resistance - open circuit or infinite resistance meaning it has permanently failed and needs replacing.

SFK

 

[T5 TDI]

Yes I think that is it. I checked it earlier and it has continuity across the terminals so I guess it's not that.

Edit- Aha! I've just found a melted connector on the lower of the three door latch micro switches. The lower latch has two switches and this melted wire is a thick grey one that links the two. It's quite welded to the switch. If I could get it off I could clean it up as a temporarily test.

What do you think? It could be an unconnected fault that hasn't caused a problem yet although it looks pretty bad to me. I'd be condemning that if I found it on a car I was working on!

 

[SFK]

T5,
I think you know all teh stuff I am about to say... but so recorded.

Seems to have been a bit of power to have done that - likely to have damaged switch too - and maybe other things.
I would pull off wire. Then Check operation of switch with multimeter using continuity setting.
If Switch okay reconnect. But I would worried as you have not found or fixed the cause of all that current going though switch.

If Switch broken, pull switch out and look for any writing and try and find similar one.
I would not try and hot wire connection (even for a trial run) as that might allow door to be open at same time as oven is on.
SFK

 

[T5 TDI]

How strange! That's exactly what I have done. I did wonder about the cause. On cars I've seen stop light switches fail inside and cause that. Mind you they are often poor quality. The switch has a melted terminal pin but it did work according to the meter. I think I will risk a new switch and connector and see what happens. Thanks for the tip about not hot wiring it. I don't want to microwave myself!

So far I haven't found one for under £20 with P&P.

 

[T5 TDI]

I just looked at the wiring diagram and the grey wire that has overheated goes directly to the turntable. That seems a lot of current for a little microswitch. The grey wire is a nice thick one and the heat looks to have been very local to the switch as if the the heat was actually caused inside the switch. There is no sign whatsoever of the wire overheating along its length. So it's finger's crossed..

 

[SFK]

It LOOKS like a standard:
Microswitch SPDT 16A Micro Switch
https://www.ebay.co.uk/sch/i.html?_...R0.TRC0.H0.TRS0&_nkw=microswitch+16A&_sacat=0

But get me a bit worried that it has a different wire route.
You could get one of above for £2 and test it against the other orgional switch.
SFK

 

[SFK]

And from a reputable supplier:
http://uk.rs-online.com/web/p/produ...VQkAbCh3djgWqEAQYASABEgL43fD_BwE&gclsrc=aw.ds

 

[SFK]

I would presume that failure caused by pitting of the internal switch plates, increasing resistance, increasing heat, causing mechanical failure of switch (it melts until plates hopefully separate).
But surprised that wiring diagram shows the switch only powering the turntable (which before you said was working?)
SFK

 

[T5 TDI]

But surprised that wiring diagram shows the switch only powering the turntable (which before you said was working?)
SFK

That seems to be all that is being powered from that switch (there are three though) The thicker grey wire feeds the turntable. The other two much thinner wires go to the next switch and the other to what could be a terminal block of some kind.

The lower latch trips two of the switches at once as it moves so they seem to be working together. Perhaps it's some kind of fail safe mechanism so that both switches have to agree the correct switch position before power can be supplied to the magnetron? Cars have door switch position monitoring so that the car 'knows' if each door is open or closed or even if it is on the safety catch. Other systems on the car use this info (like 'You've left the lights on you idiot' chimes and the car's own alarm system). I notice they call the (melted) oven switch the 'monitored latch switch' and the one next to it 'monitor switch'.

That's a good point about the turntable. I never actually saw the turntable working so I'm really hoping it wasn't! I was more focussed on confirming the individual heat sources weren't working. The light was working though and the oven made all the usual noises. I'm sure I heard the convection fan too. It was funny, I put a glass of water in there on microwave for a minute and at the end of it my brain didn't quite want to accept that the glass was still stone cold!

 

[T5 TDI]

SFK- Apologies, I entirely missed your posts with the links somehow. Do the specs on the side look reasonable compared to mine? They both say 16A and 3A so I'm guessing the 16A is the max peak (when it starts up) and 3A is the continuous rating. The switch in your second link looks perfect to me. As long as the specs match I will test it first against mine for function with a meter as you say and watch it carefully in operation for a while.

 

[SFK]

My reading is that it is exactly the same as yours and is the one I would buy.

Good question about the 16(3)A rating. I have never considered what that means as have always assumed okay for 16A continuous. However I do believe that Microswtches so not like low currents as this can also damage the switch contacts. PERHAPS it is a greater than rating (or should be used for 3A to 16A applications. But as said I do not know.

Sfj

 

[wv62]

It looks like a V3 micro switch. Available from any good parts suppliers such as RS or Maplin (spit!!). The 16(3)A normally refers to the max current either resistive (16A) or inductive (3A) at 250V