Usual failure modes of magnetrons?

Magnetrons are still vacuum tubes with heaters in them. They are probably made in China and quality control is letting crap out the door.

Paul

I think the

has information about diagnosing microwave ovens.

I had one magnetron fail when its permanent magnet (3" or so disk with a large hole in the middle) cracked, and another one developed a short in one of its feed-through capacitors where the high voltage went into it.

How did you measure the "really high voltage going to the magnetron"???

Sorry, you are wrong. CE aka China Engineering aka Crap Enforcement doesn`t let quality in, so there is no quality production :]

Saludos Wolfgang

--
Wolfgang Allinger              15h00..21h00 MEZ: SKYPE:wolfgang.allinger
Paraguay            mailer: CrossPoint XP 3.20 (XP2) in WinXPprof DOSbox
Meine 7 Sinne:                                    reply Adresse gesetzt!
Unsinn, Schwachsinn, Bloedsinn, Wahnsinn, Stumpfsinn, Irrsinn, Loetzinn.

snipped-for-privacy@whidbey.com wrote in news: snipped-for-privacy@4ax.com:

usually,the MW output drops,perhaps from reduced cathode emission. or the filament opens,they don't last forever. :-) or internal arcing causes the PS fuse to blow.

Not much else to go wrong.

--
Jim Yanik
jyanik
at
localnet
dot com

Yes, that is true, in some cases. On the other hand, I buy GPS receiver assemblies, complete with antenna, by the thousands from China and have never had a bad one.

Paul

Good to hear, that not every product is controlled by Crap Enforcement :)

Saludos Wolfgang

--
Wolfgang Allinger              15h00..21h00 MEZ: SKYPE:wolfgang.allinger
Paraguay            mailer: CrossPoint XP 3.20 (XP2) in WinXPprof DOSbox
Meine 7 Sinne:                                    reply Adresse gesetzt!
Unsinn, Schwachsinn, Bloedsinn, Wahnsinn, Stumpfsinn, Irrsinn, Loetzinn.

As someone said, there's not much to go wrong on the power side. Magnetron can fail, either catastrophically or go low gain and not oscillate. There's a HV transformer with a pile-wound secondary that could short out (likely blowing a fuse) and a voltage doubler diode/ capacitor that could fail (either, but a cap failure would take out the diode.) See

Safety! Microwave oven can give lethal electric shocks! Never try to measure ANY voltages while oven is ON. Always discharge the HV capacitor before touching ANY connection in the MW oven. See safety note on above website. If you don't know what you are doing, DON'T try to fix MW ovens. Cheers, Roger

** Magnetrons for Sharp microwave ovens made in China back in 1986 ????

That was the era when Japan and Taiwan were dominant.

.... Phil

"Jim Yanik"

** Must be some cases of loss of vacuum.

Affects lots of valves, big and small.

.... Phil

I've dissected a few microwave ovens to salvage transformers and for fun.

I've found cracked magnets on a few magnetrons.

I don't know if a cracked magnet would cause the failure of a magnetron, if that was the root cause of the failures or if some other failure caused the magnets to crack.

--Winston

Every one I have ever salvaged had low magnetron output or a bad HV transformer. Never seen a cracked magnet. But those old magnets are great for fooling around with as they ar so strong.

(...)

I wonder if a cracked magnet could cause low microwave output?

Sounds like a chicken and egg problem. Excessive power dissipation in the magnetron might cause a magnet to crack. (Line transient perhaps?) The cracked magnet would push the magnetron away from cutoff, forcing it to dissipate more power which heats the magnets, etc.

--Winston

re

Like you we have a small Goldstar oven that we got as an incentive for visiting a time share back around 1985. The thing has a simple wind up clock timer that rings a bell when it runs down. It too has worked flawlessly all these years. I've been repairing consumer electronics all my life and although I've never heard the term before I firmly believe that "crap engineering" is in everything today and is definitely alive and well in China. Lenny

are

I'm old enough to remember when we used to pick up a 'broken' item and pretend to read a label on it, musing out loud, "Oh, I see what's wrong. MADE IN JAPAN." ThenJapan got their act together and became one of the best suppliers of high quality opticselectronics/musical instruments.

So, ...the lesson? it is apparently far easier to continue to make things cheap, but learn how to make them well rather than continue to make things well, but learn how to make them cheap. Shudder

ts are

So the "lesson" is: don't throw out your old stuff. Maintain it as long as you can because, (and sadly), "they just don't make em like that any more".....Lenny

HV

nets are

r p

True. You're talking to a guy that spent 3 hours to fix an $8 hairdryer. The hairdryer worked longer after the 'fix' than it did between purchase and failure.

Same with a repaired Hamilton Beach Brew Station Deluxe Coffee Machine. Originally a company had it in service for 1 year, it broke, they 'threw' it away. I repaired it and it has been working in our firm for over two years and is still going!

magnets are

The new planned obsolescence.

agnets are

Hey Lenny, A repairman once told me that opening the door before the timer stopped the operation was bad for the magnetron. He said the unexpected interruption w as a shock that over time led to more frequent magnetron failures. Do you have any knowledge or opinion about this? Thanks in advance.