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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details. |
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1st Nov 2021, 8:49 pm | #21 |
Hexode
Join Date: Feb 2018
Location: Durham, County Durham, UK.
Posts: 325
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Re: Microwave oven - bizarre circuit??
it is quite common for the hv capacitor to s/cct .it is also best to replace the hv diode [for the cost of them] a lot of the more recent ovens also have a hv fuse from the transformer to the cap .only last week had exactly the same happen to our 6 year old bosch one .we used to repair lots of microwaves for private customers as well as manufacturers
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2nd Nov 2021, 10:04 pm | #22 |
Heptode
Join Date: May 2015
Location: Bradford, West Yorkshire, UK.
Posts: 512
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Re: Microwave oven - bizarre circuit??
When I have repaired my OLDE microwave, I have found that it's the heater/kathode that has gone short to ground, now on it's 3rd second hand magnetron in 12 years. The replacement magnetrons were taken from scrappers of unknown ages/history.
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worried about the electrons entering the circuit and the smoke leaving Andrew |
3rd Nov 2021, 1:15 am | #23 |
Heptode
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 962
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Re: Microwave oven - bizarre circuit??
Hi danger taking the magnatron to peices,as Most magnetrons have beryllium oxide (beryllia) ceramic insulators, which are dangerous if crushed and inhaled, or otherwise ingested. Single or chronic exposure can lead to berylliosis, an incurable lung condition the same for some RF output transistors Mick
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3rd Nov 2021, 10:16 am | #24 | |
Dekatron
Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,093
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Re: Microwave oven - bizarre circuit??
Quote:
It raises the question as to how far back one has to go to find that a branded product was actually made by the company concerned - themselves - rather than having it all subbed out to China. |
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3rd Nov 2021, 10:33 am | #25 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,995
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Re: Microwave oven - bizarre circuit??
Another feature of the design of the microwave oven transformer and rectifier relates to the magnetron heater.
It is a problem with magnetrons that at full power the cathode is subject to back bombardment which will cause it to overheat unless the heater power is reduced to compensate. The transformer is designed so that at switch on when there is no HT current being drawn, the heater voltage is the normal value but when the magnetron is up to temperature and starts to draw HT current the saturation effect in the transformer leads to a reduction of heater voltage which accommodates the back bombardment. Cunning, but now obsolete since microwave ovens now use inverter power supplies which are lighter and more efficient
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3rd Nov 2021, 1:03 pm | #26 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,858
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Re: Microwave oven - bizarre circuit??
Not quite so obsolete.
My old AEG built-in combi started failing and it looked to be the microwave transformer primary. So I needed a new cooker.... but one of the right dimensions to slot into the existing space. After rather a lot of searching I found one. Also an AEG, but unfortunately it was a top of the line model and thus badly overpriced it was a new model and supplies were only just starting. So I bit the bullet and went to my usual supplier to get one ordered. A couple of days later they contacted me saying they'd had an email from AEG declining the order because only a small list of dealers were allowed to order those! What? a manufacturer blocking their own sales? So the search went on to find somewhere that could order one. Eventually one got ordered and I went and collected it earlier in the day that lockdown first started. Did I say it featured internet connectivity? It didn't feature any explanation of why I should want to enable this. Triggering a microwave cooker remotely sounds stupid, and having it open to all the black-hats of the internet is beyond stupid. Anyway, a latest, top line model, and it has a damned heavy transformer.... David In the avionics job, I had a lot of dealings with RF power semiconductors and the firms making them see solid-state microwave cookers as the next big thing. So far they have 300W output devices on 50v DC supplies and are thinking of multiple RF paths.
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3rd Nov 2021, 1:13 pm | #27 | |
Dekatron
Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,093
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Re: Microwave oven - bizarre circuit??
Quote:
Our new* washing machine has the same idea but is hacker-proof. That is because it does it using an accoustic modem (incredible that the idea of doing that is still remembered). So the only way it connects to anything is if you stand there holding a phone up to its speaker. ( *GMB defintion of new. It may be older than I think). |
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3rd Nov 2021, 1:46 pm | #28 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,995
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Re: Microwave oven - bizarre circuit??
A lot of people would see an old built-in microwave oven starting to fail as the ideal excuse to bring forward the obligatory once-in-a-decade kitchen replacement.
My current microwave/groll/combi-oven thing I bought in 2007 when I moved here; it's silver and replaced a 3-year-old one which was white. White did not match the rest of the appliances in the kitchen so it had to go. After 15 years of relatively light use it's starting to get a bit shonky. I'm looking at a kitchen refurb.
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I'm the Operator of my Pocket Calculator. -Kraftwerk. |
3rd Nov 2021, 1:59 pm | #29 |
Dekatron
Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,093
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Re: Microwave oven - bizarre circuit??
I do not understand this. We only ugrade a kitchen when we buy a house and we are on our second and last one. So our new* kitchen is about 30 years old, but the microwave and main oven came from the old house so are much older.
Now I think about it, the microwave is the only one we have had in our main house. |
3rd Nov 2021, 2:24 pm | #30 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,995
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Re: Microwave oven - bizarre circuit??
My existing kitchen is 16 years old. Showing signs of wear - burnmarks knifemarks and dents on the wood worktops, some cracked floor/wall tiles, appliances with the lettering worn off the controls, questionably-accurate thermostats, cabinet doors no longer closing smoothly. It just _looks_ tatty, tired and so very early-21st-century. I need more power-outlets too.
Not sure if this time I'll go for a combi grill/oven/microwave though.
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I'm the Operator of my Pocket Calculator. -Kraftwerk. |
3rd Nov 2021, 2:36 pm | #31 |
Moderator
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,857
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Re: Microwave oven - bizarre circuit??
I think the OPs original queries have all been covered its time for the little ding to sound on this one.
Cheers Mike T
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Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk |