Microwave repair

Oh, and how universal are the "so called" universal motors?

AIUI the only universal thing about them is that they could work on AC or DC, which is unlikely to be an available choice in the context. Just a kind of brush using motor.

Wouldn't a synchronous motor have "some difficulty" running on DC?

The phrasing of "universal microwave motor" rather than "microwave universal motor" implies to me more about what it's intended to fit, that how it works internally, but interested to hear other opinions ...

OIC, a totally dfferent animal! (In my defence, you did say 'universal motor'.)

The turntable on ours stopped working five years ago. It still heats things up, although not quite as well.

Built in microwaves seem to have come down in price.

In the majority of cases you don't even have to remove the cover to replace the turntable motor. at the bottom of most ovens there is a knock-out hatch that you remove with a rat-tail file or similar. It has lugs so it can be re-fitted in a different orientation , they often even supply the self-tapping screw to secure it parked in a hole.

As for the universality of the synchronous motors, they are usually the same size and rating, but the spindle length (usually half-round) can vary.

When the turntable motor on my microwave died, a few years ago, I just looked on eBay for a replacement with the same size shaft and mounting holes. I fitted it. It worked. It happens to rotate at 4rpm when the other one had been geared to rotate at 5 but that was the only difference.

Nick

I presume the reason many of the motors specify 5/6th of an rpm, is because they were designed for 1rpm in 60Hz land.

TBH, this one is poor enough at heating evenly /with/ the turntable...

I thought I remembered that sort of arrangement from a previous M/O this one being built-in I haven't looked underneath it yet.

well, the built-in version has some extra ducting underneath and a radiator panel behind the normal case, secured with self-tappers, so far so good ...

... except I'd inadvertently made life difficult for myself, when fitting the under-cabinet lighting, I had managed to thread one cable (with just 2" of slack) straight between the oven and its radiator panel trapping it inside the cupboard!

Yep, it's a common TYJ50-8A7 motor, I think I'll go with £6 from eBay, rather than £45 one with a Neff sticker on it

There's usually a panel on the bottom for gaining access. They used to be screwed on, but nowadays, you have to cut a few thin bits of metal to remove them as it's all a single piece of punched steel. Refitting requires re-orienting the cover so that the screw holes line up, and finding some self-tapping screws to screw it back on.

The same motors turn up in many microwaves, except there are different thicknesses of them, and hence some won't fit in other ovens.

Yes, very cheese-paring, leaves various sharp bits of metal to cut the un-wary, just for the sake of one fewer self-tapper on the factory ...

Interestingly, a friends light went out in the microwave and the turntable stopped as well, apparently in that case both work off a low voltage and the fuse had merely blown when the bulb died. Still nobody said these were not made to a price!

Brian

IMO, the danger from microwave HV PSUs is a little overstated and little different to CRTs and the common sense needed.

I was once given an expensive combi job to mend and to test it was magnetron failure I plugged the magnetron into a £30 Argos one to check it was still duff (it was.) While fiddling in both I measured the voltage on the HV caps and they discharged *very* quickly. I think there were some fairly obvious resistors in parallel.

YMMV, naturally.

There should always be discharge resistors & normally are. That does not st op one failing, nor do they offer any protection when the machine is powere d.

The hazard is very different to CRT EHT. The latter does not normally give enough current to kill. Microwave HV PSUs provide enough to kill a whole qu eue of people in one shot.

NT

Then discharge the cap.

There are several videos on YouTube that show you how to safely do this.

You might need to buy a resistor etc

Apprentices and/or students can be used :-)

I think they only work once.

It could be as simple as a drive belt having snapped. Our first uwave, one of the early ones, used a simple O ring style drive belt. It was the only thing that actually failed in about 17/8 years. It ended up going to the tip simply because it looked 'tatty' in the new kitchen. If it is the drive belt, try a plumbers' merchant- I got one for the princely sum of 35p (although that was some years back).

As for the capacitor etc, just take care. The EHT parts are (normally) well away from the turn table motor etc and pretty obvious.

If it is more serious than than the belt, I would think there is a reasonable chance you can still get a motor. The parts tend to be used in a number of makes and, if you know the model, there are loads of companies selling either original or pattern parts. You could even try a local, small, repair place, they may have a scrap uwave with a good motor they will let have for a few quid.

The worst thing is if it is something on the control board. If you are able to solder and know what a dry joint looks like, have a check for those. Since the advent of lead free solder I've noticed a lot more dry joints in domestic items. A bit of attention with a soldering iron and all is well.

As for replacing the whole unit, they are a standard size so getting one that will fit shouldn't be an issue. Getting one that matches the other appliances may, of course, be more of a problem.