Microwave oven woes...

A client left a faulty microwave oven at my friend's shop, I opened it up and first thing I checked was, of course the HV fuse. It was open so
a new one. Nothing. Checked with my HV probe, at the transformator secondary 3.5 kV(AC). At the magnetron nothing, no DC at all. Thought it was the HV capacitor or the HV diode.Took them home, measured the capacitor with my capacitance meter, 1 ?F ok. Checked with my insulation tester that can put up to 1000 volts, the diode, forward bias 0 ?, reverse bias >10 ?? ok.Of course I didn't do anything as when you repair household appliances you must be absolutely sure you'll repair it, there's no room for experiments.Anyone with a brainwave? Again, the trafo AC ok, DC nothing-something wrong with the magnetron?
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On Friday, 7 April 2017 10:53:18 UTC-4, Tzortzakakis Dimitrios wrote:

tion

ou repair

I fixed mine last week as the breaker kept tripping randomly and then the f use and it was the Cap shorted. Check coil on hipot then magnetron tube f or leakage
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On 9/4/2017 1:05 ??, Anthony Stewart wrote:

so you think it would be hte capacitor??(that's a rhetorical question as we gave the oven to the customer back as I wasn't sure). we found a new capacitor but if that wasn't the case we would be left with a useless capacitor and at least with 15 euros less. the fuse didn't blow again, 1.7 kV at the secondary, AC but no DC at the magnetron so it must have been something at the voltage doubler.
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Fri, 07 Apr 2017 14:53:06 GMT in alt.engineering.electrical, wrote:

What is the make/model of the meter you've mated the HV probe with to test the voltage coming off the transformer?
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On 21/4/2017 1:56 ??, Diesel wrote:

It's the Benning MM-1. A very good one, I think. I think I followed the correct procedure or I wouldn't be here talking to you:-) The HV probe's division factor is 1000, that means that 3.5 kV will appear in the multimeter as 3.5 volts. The probe's manual says never to choose auto range, and make sure that the input impendance of the multimeter must be at least 10 M?. If the input impendance is 1 M?, then it's 2000.That means 1 kV becomes 0.5 volts. I don't know the input impendance of my multimeter, I did a google search obviously which turned out nothing. I have tested the HV probe measuring line voltage 0.22 kV ok.
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Fri, 07 Apr 2017 14:53:06 GMT in

Thanks! Which HV probe are you using? I forgot to ask previously. :)
I've been thinking about the Fluke 80K-40. I just need to see if the DMMs I've presently got are satisfactory for it. I've been wanting to test HV transformers (neon sign, microwave, etc)...
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On 23/4/2017 1:24 ??, Diesel wrote:

It's a Testec TT-HVP 40 max.ac 28kV and dc 40 kV. I don't know if you could test a neon sign transformer as it measures only line to earth and not line to line. That means that it has an earthing alligator clip which MUST be used and the HV source must have its minus (or neutral) earthed. The german term is "ruckleitung", must be earthed. I ordered it online from www.reichelt.de, I recommend them, good prices, excellent service, 88 euros. I ordered the rest from them (capacitance meter, insulation tester, installation tester etc.) Problem-catalogue only in german! Not a problem for me as I have been taught german since a boy, but is for everyone else, of course.The Fluke must be better!
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Sun, 23 Apr 2017 17:57:08 GMT in alt.engineering.electrical, wrote:
[snip]

Hmm. I'm not so sure it's any different in the connection aspect.
http://en-us.fluke.com/products/all-accessories/fluke-80k-40.html http://media.fluke.com/documents/80k40___iseng0900.pdf
I could be confused here, but, don't you clip the alligator to neutral/ground and then probe the line/positive? As, internally, atleast with the fluke, the ground clip and the common on the banana pin are electrically connected. IE: the same? It would appear to me, atleast, that yours is also wired in the same manner.
http://www.newark.com/testec/tt-hvp-40/test-probe-high-voltage-multimeter/dp/10C3016?CMP C_OP
This is what I found for neon sign transformers: http://www.signindustry.com/electric/articles/2003-05-08-EssentialToolsofTrade.php3
Am I missing something here with your line to line reference? I can't seem to find an HV probe that distinguishes between line to line and line to ground...As, the alligator clip appears to be electrically wired to the common pin coming from the HV probe.
http://rimstar.org/equip/hv40kvprobe.htm
Btw, I found a very good resource for microwave testing and repair:
http://www.repairfaq.org/sam/micfaq.htm
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On 24/4/2017 2:11 ??, Diesel wrote:

sorry, my mistake-I meant the common from the HV supply, where you will connect the ground pin for the HV probe must be earthed. So, for instance you wouldn't be able to measure MV here, in Greece where it's 3 phase without a neutral or a common wire earthed-you wouldn't of course measure line, to line that's what I meant-do neon transformers have an earthed com?I thought they were not.
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Sun, 23 Apr 2017 17:57:08 GMT in

Hmm. How were you able to take measurements from the Microwave transformer? I'm confused. :(
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On 26/4/2017 4:36 ??, Diesel wrote:

as bud said, it has a ground referenced secondary-at the ground you connect the HV probe's ground, and you touch the tip of the probe to the HV end of the secondary, after the fuse with the meter in AC. Normally it's 1,7 kV. And then with the meter on DC at the point where the magnetron's supply is, normally 3 kV DC I think. you must be absolutely sure you follow the correct procedure as the voltages in microwave oven are very dangerous (goes without saying).
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Sun, 23 Apr 2017 17:57:08 GMT

Yes, I know this. Your description of the electrical configuration in greece is what confused me. That's why I asked how you were able to test the transformer if you didn't have a ground/neutral line to connect the alligator clip to, since, without doing so, no circuit gets completed; rendering the probe useless. AFAIK, It's not the voltage by itself which makes it a dangerous one to test, but that it's also pushing atleast one amp behind it. If it doesn't outright kill you, it would probably make you wish it did, when you wake up, on the floor someplace. Right? :)
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On 27/4/2017 5:57 ??, Diesel wrote:

I didn't test it, I haven't got suicidal tendencies yet;measuring a high-energy 20kV MV circuit with at least 100 Amperes is not of any interest to me;that's the utility's job anyway and I think they do it with potential transformers. A scrap thief ring was uncovered lately;the "brain" of the ring had complete knowledge of how to dismount the MV/LV utility transformers, complete with utility poles to open the disconnect switches and pull down the trafo at his leisure. He had more than 800 kilos of copper at his disposal. That's more than 8000 euros in money.I think they arrested him and put in jail straight away;in such cases they are taken immediately to court, it's called "aftoforo"in greek.It's very dangerous to measure a HV circuit without connecting the earthing alligator clip, but I suppose you already know this...
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Thu, 27 Apr 2017 19:03:33 GMT in alt.engineering.electrical, wrote:
[big snip]

Ahh. 100 amps? WOW. I thought you were discussing a consumer unit. :) I'm not interested in measuring anything that high up the ladder either. I'm not afraid of dying, but, why rush it, right? :)
I just want to be able to take mostly accurate measurements of consumer/commercial grade HV transformers like the ones found in microwaves. For my own personal knowledge gain. Mostly. I like being able to fix things, and, without knowing if the transformer is pushing what it should be, I can't confirm/deny the transformer itself is okay or not. So, that's why I asked you about the probe. I'm not the kind of person who replaces parts until it works again. I prefer to replace the parts I know are bad, instead of guessing.

I can't stand a thief. Yes, I know what the clips for; besides completing the circuit and providing more protection for me from getting turned into a piece of charcoal. It also greatly reduces the chance that if an internal failure occurs in the probe itself, I don't blow up my meter and/or myself.
As in, literally blow the meter up. I'm sure you know what happens if you take a hand held meter and greatly, beyond all reaslitic expectations exceed what it's designed for. Not the meters fault either. That would be entirely on me. You seem to be quite knowledgeable on the subject of electricity. Are you an engineer of some kind?
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On 28/4/2017 3:41 ??, Diesel wrote:

okay, maybe it's 12 A, never measured it, though.
exactly, I agree. that's the point of it, anyway.
not just the fuse, it would blow the whole meter.
I am an electrical engineering major and I have graduated from the college here, Iraklion, Crete, Greece:-) And with an apprenticeship under my belt I know a few things, because just the degree is not enough;-)
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On 4/23/2017 11:57 AM, Tzortzakakis Dimitrios wrote:

Far as I know all neon sign transformers in the US have a ground referenced secondary. For instance, a common 15kV transformer has a secondary center-tap connected to the case. Likely common practice elsewhere.
Neon sign transformers are basically constant current sources. The voltage from a loaded transformer might be 80% of the rated voltage.
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