Microwave repair

While warming up the cup of coffee I'd forgotten to drink, I stood there noticing the slight break-up on the bluetooth speaker that's right next to the microwave ... until I noticed something else, the damned turntable is no longer going round.
Can turn the spindle by hand, and tell that it's quite highly geared, it's an 8 year old stainless Neff. Since it's built-in and was difficult to find one to fit, I'd prefer to repair rather than replace.
I realise the dangers from the capacitor until discharged, and the beryllium oxide bits, and presume that making sure it's well and truly back together before powering it back on avoids any trouble from tripping the interlocks.
That said I expect to be able to get at the turntable motor/gearbox without going near the "active" end ... any other gotchas?
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Andy Burns wrote:

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

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Roger Hayter wrote:

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 ...
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OIC, a totally dfferent animal! (In my defence, you did say 'universal motor'.)
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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
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On 12/03/2018 11:43, Roger Hayter wrote:

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.
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GB wrote:

TBH, this one is poor enough at heating evenly /with/ the turntable...
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On 12/03/18 11:39, Andy Burns wrote:

They tend to be the larger motors sometimes used in washing machines. The motors used to drive turn tables in uwaves (and water pumps in washing machines and dishwashers) are small, AC, motors.
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On 13/03/18 11:39, Brian Reay wrote:

I dont think so for washing machines and dishwasher. Fairly sure the ones I have taken out were brushed.
I agree with µ-wave turntables being synchs tho.
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On 13/03/2018 12:26, The Natural Philosopher wrote:

Universal motors of the type I'm describing have brushes.
I don't recall seeing one in a dishwasher but I've not looked at many so that isn't conclusive.
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Main wash pump motors that I've seen in dishwashers are all 2-phase with a run capacitor.
The waste pumps in dishwashers and washing machines are all shaded pole motors.
Drum motors in washing machines are universal motors (i.e. with brushes) when belt driven, and stepper motors (brushless) when direct drive. Drum motors need good starting torque and a very wide speed range, which the other motors above don't have.
I can still recall my parents' first washing machine, which predated any sort of electronic motor control. I'm not sure what the motor was, but it was single speed, single direction. It had a sodding great gearbox attached with a handful of large solenoids around it to do the gear changes. I can still clearly recall the loud bangs as the different solenoids engaged to change the drum speed throughout the program. When it was scrapped, I saved the mains solenoids and some other parts, which got used in a few projects afterwards. They did tend to overheat, as the washing machine was for 200V mains, and had been converted to 240V when the mains voltage changed by fitting a large autotransformer inside the case, which I hadn't kept because it was too heavy.
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On 16/03/2018 22:55, Andrew Gabriel wrote:

When did the machine date from? Was it an early automatic? My parents had a single drum followed by a twin tub, neither of which required a gearbox or speed controls I imagine as the motors drove dollies and impellers and pumps and mangles and spin driers.
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I misread that as singular "motor" at first, and had this brief mental image of your parents' scullery with a long shaft across one side of the ceiling and a row of domestic appliances all with their own (unguarded in my image) belt drives from the ceiling. Silly, I know.
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English Electric Liberator, would have been 1961 or 1962. Yes, it was automatic.
https://www.gracesguide.co.uk/images/0/07/Im20110618Bak-EE-Liberator.jpg
(not my parents' actual one, but identical)
You turned the red dial to show the program you wanted in the window, and then selected the number it showed on the dial on the right, which slowly turned to go through the wash cycle. There were contacts on both dials, which combined to form the wash cycle program. The red dial showed 1-3 different programs, and the right dial selected which of those it was going to do.
The only thing I ever recall going wrong with it was the clutch, which allowed the drum inertia to freewheel when it was spinning and the gearbox changed down gear for a slower speed without back-feeding the gearbox at high speed. It was a large coil spring slid over the drum shaft which gripped the shaft when driven by the gearbox, but relaxed grip if the drum was turning faster than the gearbox output. (The machine could not reverse the direction of the drum.) The spring broke after around 12 years, but a replacement was obtained and fitted by my father.
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We had a Hotpoint Liberator about 15 years later, we must have had it for 10 years until the bearings gave up, and I replaced it with an identical machine from my parents-in law cellar that had little use.
The first front lording automatic I ever saw was at my next door neighbours when I was a kid. A Bendix. I was very impressed.
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On Sat, 17 Mar 2018 20:33:41 +0000, Graham. wrote:

I was quite impressed by the more modern day "Tricity Bendix" (a fourteen years old re-badged Zanussi) which I had to repair a week or so back. The innards looked as pristine as the day it was made (the poor old 16A 700v triac, otoh, only *looked* pristine - it had finally succumbed to the abuse our youngest son had been meting out to the machine[1].
I was quite surprised to see such an *actual* improvement in washing machine design in the intervening two decades between the 1983 Servis Quartz that I'd kept running right up until the day we swapped it out for that Tricity Bendix. If the current crop of Zanussi based washing machines have maintained this standard, I for one, am only too happy to recommend the brand.
Once our youngest (now a 35 year old "Twenty Something" Kidult) had tracked down a YT video showing how to split the casing on a Zanussi machine that looked the spitting image of our "Tricity Bendix AW 1400 W", it proved a remarkably easy machine to work on. Also, thanks to my youngest, I've replaced said triac and still have another five 'spares'.
I suspect his motivation to order one from an ebay trader, then another five from Farnell the next day to get a quicker delivery in case we *actually* had to wait a whole 8 days for the first order to arrive, was partially out of 'guilt' and mainly out of the need to get his next load of washing washed and dried (see [1] and [2] below).
When we realised the machine had an actual show stopping fault rather than it being a case of it 'sulking', his first reaction was to suggest that it immediately be replaced with a brand new machine, poo pooing my initial reaction that it would be worth taking a closer look at its innards with a view to repairing it unless some expensively critical component had failed. It took only a day for my point of view to sink in [2] before he was glibly volunteering to order the replacement triac at his own expense.
The first 800v version ordered on the Friday night from an Ebay trader, I know had cost him £5.45. The following day's Farnell order for a 5 pack of the 700v triacs, I believe a price of seven quid or so was briefly mentioned. When I later asked him what he'd paid Farnell, he avoided answering the question and the delivery note didn't show the price paid, so my best guess is that he must have shelled out some 13 quid or more just to speed up the repair process. Not a lot of money in the wider scheme of things (pocket change, really) when you consider his initial suggestion that we spend a good three to four hundred quid on a replacement machine.
[1] He's been doing this for the past decade or so, cramming a week's worth of his washing into the drum in the hope of getting the job done in one fell swoop, overcompensating by selecting the longest and most arduous of wash programme cycles available rather than splitting it and using two seperate shorter but more effective wash cycles that would still take less time than the longer cycle. He does the same thing with the tumble drier (even on good weather drying days) by selecting the maximum heated tumble dry cycle when a much shorter one will suffice. That thirteen quid or so he spent on triacs is a small enough token of atonement indeed.
[2] Also in retrospect, I suspect he could have been thinking, "If the old fool must insist on attempting a repair, the sooner he fails, the sooner we can order a new machine.". Mind you, if he *had* been thinking this, his enthusiasm to help was convincing enough to hide any such thoughts. He should go far in today's world of "Corporate Bullshit Management"(tm). :-)
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On Fri, 16 Mar 2018 22:55:15 +0000, Andrew Gabriel wrote:

I can imagine the need for a 10A rated 240v supply which would require a 400VA auto transformer in this case (40v difference at 10A) which could easily weigh some 16 to 20 Lbs. Just as you described, not a lightweight item. :-)
I can understand why you didn't hang onto it since any future need to adapt a 200v appliance to 240v mains would be extremely improbable. The only potential use would be in a museum of domestic electrical appliances. Did you ever consider donating it to any such museums?
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It was probably 20 years old, and not noteworthy at the time.
If it was still around now, I would either find a museum, or keep it going!
Although I vivdly recall the sounds it made, it kind of seems a shame there's probably no video or even audio history of such devices running remaining today.
I did record an older device which I still have working, a Hoover Constellation vacuum cleaner, playing with it as a frictionless puck much as I did as a child in my parents' house, although they had flatter floors than this one was.
http://www.youtube.com/watch?v=VXb8Fo3T5h0

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My knowledge of transformer theory was never very clear, but why is it not rated for the total output, which might well be something like 10A at 200v, 2000VA?

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