Microwave oven

[Cursitor Doom]

Hi all,

I have had the same Daewoo microwave oven since I bought it new 7 years
ago and it's always performed *perfectly* up until today. This morning I
stuck some bread in it to defrost and it came out still frozen. No trace
of any heat at all. The platter rotates, the light comes on, the timer
counts down, the fan runs; all is working fine except for the total
absence of heat.
I'm given to understand that microwave ovens typically have a working
life of only around 2 years nowadays, so I'd really like to fix this one
up rather than replace it with something inevitably inferior. Any
suggestions as to what to check for? I have the gear to measure up to
50kV if necessary, and I'd guess the magnetron HT is considerably less
than that figure. So... where to start looking first?



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On Friday, 22 March 2019 19:37:05 UTC, Cursitor Doom wrote:

Hi all,

I have had the same Daewoo microwave oven since I bought it new 7 years
ago and it's always performed *perfectly* up until today. This morning I
stuck some bread in it to defrost and it came out still frozen. No trace
of any heat at all. The platter rotates, the light comes on, the timer
counts down, the fan runs; all is working fine except for the total
absence of heat.
I'm given to understand that microwave ovens typically have a working
life of only around 2 years nowadays, so I'd really like to fix this one
up rather than replace it with something inevitably inferior. Any
suggestions as to what to check for? I have the gear to measure up to
50kV if necessary, and I'd guess the magnetron HT is considerably less
than that figure. So... where to start looking first?

Likely candidates are the HV diode & HV fuse. Of course it can be other things. And of course they're in the killer section.


NT

 

[Cursitor Doom]

On Fri, 22 Mar 2019 14:18:03 -0700, tabbypurr wrote:

Likely candidates are the HV diode & HV fuse. Of course it can be other
things. And of course they're in the killer section.

Familiar territory then. I've spent god knows how many years prodding
around inside the HT cages of CROs and whatnot.





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[John-Del]

On Friday, March 22, 2019 at 3:37:05 PM UTC-4, Cursitor Doom wrote:

Hi all,

I have had the same Daewoo microwave oven since I bought it new 7 years
ago and it's always performed *perfectly* up until today. This morning I
stuck some bread in it to defrost and it came out still frozen. No trace
of any heat at all. The platter rotates, the light comes on, the timer
counts down, the fan runs; all is working fine except for the total
absence of heat.
I'm given to understand that microwave ovens typically have a working
life of only around 2 years nowadays, so I'd really like to fix this one
up rather than replace it with something inevitably inferior. Any
suggestions as to what to check for? I have the gear to measure up to
50kV if necessary, and I'd guess the magnetron HT is considerably less
than that figure. So... where to start looking first?

The easy place to start is with the door switches. Microwaves usually have several as a fail safe.

With the microwave running, watch the interior light carefully and listen for any change in sound as you slowly rock the door. If the light dims and you hear a buzz begin, you've got a cranky safety interlock switch. There could be a broken activator tang as well and it might be visible right on the door.

Inside, the relays are known to develop cracks in the solder at the pc board, so leaning on the relay and edge connectors could restart the cooking.

 

On Friday, 22 March 2019 21:46:47 UTC, Cursitor Doom wrote:

On Fri, 22 Mar 2019 14:18:03 -0700, tabbypurr wrote:

Likely candidates are the HV diode & HV fuse. Of course it can be other
things. And of course they're in the killer section.


Familiar territory then. I've spent god knows how many years prodding
around inside the HT cages of CROs and whatnot.

That's good.

Re interlocks, they're designed to short out via a power resistor if any one fails to operate correctly. So usually interlock failure results in an oc shorting resistor - which is a hazardous state in which to run a nuke. So it's always worth checking continuity of the big resistor when you have the cover off. IME interlocks are low on the list of likely suspects.


NT

 

[Peter Jason]

On Fri, 22 Mar 2019 19:37:03 -0000 (UTC), Cursitor
Doom <curd@notformail.com> wrote:

Hi all,

I have had the same Daewoo microwave oven since I bought it new 7 years
ago and it's always performed *perfectly* up until today. This morning I
stuck some bread in it to defrost and it came out still frozen. No trace
of any heat at all. The platter rotates, the light comes on, the timer
counts down, the fan runs; all is working fine except for the total
absence of heat.
I'm given to understand that microwave ovens typically have a working
life of only around 2 years nowadays, so I'd really like to fix this one
up rather than replace it with something inevitably inferior. Any
suggestions as to what to check for? I have the gear to measure up to
50kV if necessary, and I'd guess the magnetron HT is considerably less
than that figure. So... where to start looking first?

Replacing the lamp has me defeated. I buy a new
mwave then.

 

[Cursitor Doom]

On Sat, 23 Mar 2019 10:09:02 +1100, Peter Jason wrote:

> Replacing the lamp has me defeated. I buy a new mwave then.

I don't want a new one, though! The existing one is built to an amazingly
high standard and the manufacturer has taken time and trouble to finish
it beautifully as well. I'll struggle to find anything around today that
comes close to that quality.



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On Friday, March 22, 2019 at 9:02:12 PM UTC-4, Cursitor Doom wrote:

On Sat, 23 Mar 2019 10:09:02 +1100, Peter Jason wrote:

Replacing the lamp has me defeated. I buy a new mwave then.

I don't want a new one, though! The existing one is built to an amazingly
high standard and the manufacturer has taken time and trouble to finish
it beautifully as well. I'll struggle to find anything around today that
comes close to that quality.



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Most of the tests can be done with the power off (continuity checks)...to summarize:
Ck door switches
Ck power resistor
Ck HV diode
Ck magnetron
Ck HV transformer

I won't repeat/elaborate on these but here is some detailed diagnostic techniques.
https://www.partselect.com/Repair/Microwave/No-Heat/

Ebay is a source of parts, especially magnetrons at reasonable prices. You will see the name Galant as a mfg. The produce something like 70% of the worlds magnetrons and they sell to everybody (panasonic, toshiba, daewoo, etc, etc.
Most of the others are low quality knockoffs...YMMV

You should search online for a schematic for your unit...all will become clear with that in hand. Fairly simple.
J

 

On Saturday, 23 March 2019 17:15:49 UTC, jjhu...@gmail.com wrote:

On Friday, March 22, 2019 at 9:02:12 PM UTC-4, Cursitor Doom wrote:
On Sat, 23 Mar 2019 10:09:02 +1100, Peter Jason wrote:

Replacing the lamp has me defeated. I buy a new mwave then.

I don't want a new one, though! The existing one is built to an amazingly
high standard and the manufacturer has taken time and trouble to finish
it beautifully as well. I'll struggle to find anything around today that
comes close to that quality.

Most of the tests can be done with the power off (continuity checks)...to summarize:
Ck door switches
Ck power resistor
Ck HV diode
Ck magnetron
Ck HV transformer

I won't repeat/elaborate on these but here is some detailed diagnostic techniques.
https://www.partselect.com/Repair/Microwave/No-Heat/

Ebay is a source of parts, especially magnetrons at reasonable prices. You will see the name Galant as a mfg. The produce something like 70% of the worlds magnetrons and they sell to everybody (panasonic, toshiba, daewoo, etc, etc.
Most of the others are low quality knockoffs...YMMV

You should search online for a schematic for your unit...all will become clear with that in hand. Fairly simple.
J

If it's mechanical control, the circuit is much the same for them all. And the cct is usually printed inside the outer cover. Why they're the one appliance to have that I don't know.


NT

 

[Chuck]

On Fri, 22 Mar 2019 19:37:03 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

Hi all,

I have had the same Daewoo microwave oven since I bought it new 7 years
ago and it's always performed *perfectly* up until today. This morning I
stuck some bread in it to defrost and it came out still frozen. No trace
of any heat at all. The platter rotates, the light comes on, the timer
counts down, the fan runs; all is working fine except for the total
absence of heat.
I'm given to understand that microwave ovens typically have a working
life of only around 2 years nowadays, so I'd really like to fix this one
up rather than replace it with something inevitably inferior. Any
suggestions as to what to check for? I have the gear to measure up to
50kV if necessary, and I'd guess the magnetron HT is considerably less
than that figure. So... where to start looking first?

Sometimes the relays go intermittent. Try tapping them with an
insulated probe if it isn't door switches, themal cut-off sensor,
filament connections, HV diode or capacitor.

 

[Phil Allison]

Cursitor Doom wrote:

Likely candidates are the HV diode & HV fuse. Of course it can be other
things. And of course they're in the killer section.


Familiar territory then.

** Massive false assumption.

I've spent god knows how many years prodding
around inside the HT cages of CROs and whatnot.

** There is no comparison - microwave ovens are highly lethal to repairers, hundreds of times more so than scopes.

Never play down the risk, that would be a criminal thing to do.




..... Phil

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On Saturday, 23 March 2019 21:22:36 UTC, Phil Allison wrote:

Cursitor Doom wrote:

Likely candidates are the HV diode & HV fuse. Of course it can be other
things. And of course they're in the killer section.


Familiar territory then.


** Massive false assumption.


I've spent god knows how many years prodding
around inside the HT cages of CROs and whatnot.



** There is no comparison - microwave ovens are highly lethal to repairers, hundreds of times more so than scopes.

but the techniques for dealing with EHT are the same. He's an electrical guy with experience with EHT, not a random newb.


> Never play down the risk, that would be a criminal thing to do.

did anyone? No.

 

[Phil Allison]

tabb...is a dangerous MORON

Phil Allison wrote:
Cursitor Doom wrote:

Likely candidates are the HV diode & HV fuse. Of course it can be other
things. And of course they're in the killer section.


Familiar territory then.


** Massive false assumption.


I've spent god knows how many years prodding
around inside the HT cages of CROs and whatnot.



** There is no comparison - microwave ovens are highly lethal
to repairers, hundreds of times more so than scopes.

but the techniques for dealing with EHT are the same.

** That is another dangerous false assumption.

He's an electrical guy with experience with EHT,

** More likely to make him careless with a microwave oven.

not a random newb.

** Yawnnnn....

Never play down the risk, that would be a criminal thing to do.

did anyone?

** Well, you just did and so did he.

But having wanked yourselves bind you cannot read your own posts.


> No.

** Complete fuckwits like you and CD need a giant kick up the arse.

I could not give a SHIT about either of you being electrocuted - but there are others who read these pages and they are not so deserving.



..... Phil

 

On Saturday, 23 March 2019 22:19:12 UTC, Phil Allison wrote:

tabb...is a dangerous MORON
Phil Allison wrote:
Cursitor Doom wrote:

Likely candidates are the HV diode & HV fuse. Of course it can be other
things. And of course they're in the killer section.


Familiar territory then.


** Massive false assumption.


I've spent god knows how many years prodding
around inside the HT cages of CROs and whatnot.



** There is no comparison - microwave ovens are highly lethal
to repairers, hundreds of times more so than scopes.

but the techniques for dealing with EHT are the same.


** That is another dangerous false assumption.


He's an electrical guy with experience with EHT,


** More likely to make him careless with a microwave oven.


not a random newb.


** Yawnnnn....



Never play down the risk, that would be a criminal thing to do.

did anyone?


** Well, you just did and so did he.

But having wanked yourselves bind you cannot read your own posts.


No.

** Complete fuckwits like you and CD need a giant kick up the arse.

I could not give a SHIT about either of you being electrocuted - but there are others who read these pages and they are not so deserving.



.... Phil

I'm pretty sure how I approach it is safe, but enjoy your trip.

 

[Cursitor Doom]

On Sat, 23 Mar 2019 17:16:57 -0700, tabbypurr wrote:


> I'm pretty sure how I approach it is safe, but enjoy your trip.

Phil would probably like to see me and several other posters here dead if
the truth be known. There is so much hatred in that man. Fortunately,
since I perma-plonked him some time ago I rarely have to see his so-
called "contributions" any more.
I could accept Phil's attitude problem if he gave 100% accurate advice,
I'd happily ignore all the bile as a personality quirk, but he's
frequently wrong and when that's pointed out to him he invariably attacks
whoever exposed it in the most visceral way. I struggle to see how
personal attacks are going to improve his credibility, but if that's what
he believes there's nothing you or I or anyone else can do about it.





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[Cursitor Doom]

On Sat, 23 Mar 2019 10:15:46 -0700, jjhudak4 wrote:

Most of the tests can be done with the power off (continuity
checks)...to summarize:
Ck door switches Ck power resistor Ck HV diode Ck magnetron Ck HV
transformer

I won't repeat/elaborate on these but here is some detailed diagnostic
techniques.
https://www.partselect.com/Repair/Microwave/No-Heat/

Ebay is a source of parts, especially magnetrons at reasonable prices.
You will see the name Galant as a mfg. The produce something like 70%
of the worlds magnetrons and they sell to everybody (panasonic, toshiba,
daewoo, etc, etc.
Most of the others are low quality knockoffs...YMMV

You should search online for a schematic for your unit...all will become
clear with that in hand. Fairly simple.

Many thanks for that info. This is also worth a look:

https://tinyurl.com/y4gh8cdb




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[Trevor Wilson]

On 23/03/2019 6:37 am, Cursitor Doom wrote:

Hi all,

I have had the same Daewoo microwave oven since I bought it new 7 years
ago and it's always performed *perfectly* up until today. This morning I
stuck some bread in it to defrost and it came out still frozen. No trace
of any heat at all. The platter rotates, the light comes on, the timer
counts down, the fan runs; all is working fine except for the total
absence of heat.
I'm given to understand that microwave ovens typically have a working
life of only around 2 years nowadays, so I'd really like to fix this one
up rather than replace it with something inevitably inferior. Any
suggestions as to what to check for? I have the gear to measure up to
50kV if necessary, and I'd guess the magnetron HT is considerably less
than that figure. So... where to start looking first?

**First off: As Phil has stated, these things are VERY dangerous.
NOTHING like working on the EHT of a TV set (which certainly can bite).
2kV+ of DC WILL kill. No doubt about it.

Next: If it has a big ole' transformer (easy to tell, if you need two
hands to carry it), it should be an easy fix. Diode or magnetron. Most
likely the magnetron, though they usually fail slowly, due to emission
loss. It could be something else though.

Lastly: If it employs an SMPS, rather than a big lump of iron and
copper, dump it and buy a new one. Not worth the effort.


--
Trevor Wilson
www.rageaudio.com.au

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[Phil Allison]

Cursitor Doom wrote:

Phil would probably like to see me and several other posters here dead if
the truth be known.

** Just all the trolls - like you.



> There is so much hatred in that man.

** Yep - I hate trolls.

They ruin newsgroups for everyone.

Fortunately,
since I perma-plonked him some time ago

** What a gutless waste of space you are.

I could accept Phil's attitude problem if he gave 100% accurate advice,

** No such thing is possible or required of anyone here.

You are completely insane.

I'd happily ignore all the bile as a personality quirk, but he's
frequently wrong

** FFS prove it - not once have you ever done that.

You lying pile of shit.



...... Phil

 

[Cursitor Doom]

On Mon, 25 Mar 2019 04:38:56 +1100, Trevor Wilson wrote:

**First off: As Phil has stated, these things are VERY dangerous.
NOTHING like working on the EHT of a TV set (which certainly can bite).
2kV+ of DC WILL kill. No doubt about it.

*CAN* kill. *Not* WILL. Depends on *several* factors so your "no doubt
about it" is incorrect.
There is one large fat potentially-lethal capacitor in there that needs
to be discharged as the first job to do after the removal of the outer
casing. It doesn't appear to have a bleed resistor for some reason (not
with this particular oven anyway.)





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On Sunday, 24 March 2019 14:26:10 UTC, Cursitor Doom wrote:

On Sat, 23 Mar 2019 17:16:57 -0700, tabbypurr wrote:


I'm pretty sure how I approach it is safe, but enjoy your trip.

Phil would probably like to see me and several other posters here dead if
the truth be known.

I don't doubt it.

There is so much hatred in that man. Fortunately,
since I perma-plonked him some time ago I rarely have to see his so-
called "contributions" any more.
I could accept Phil's attitude problem if he gave 100% accurate advice,
I'd happily ignore all the bile as a personality quirk, but he's
frequently wrong and when that's pointed out to him he invariably attacks
whoever exposed it in the most visceral way.

Yup

I struggle to see how
personal attacks are going to improve his credibility, but if that's what
he believes there's nothing you or I or anyone else can do about it.

It would be sensible to say microwaves can electrocute people, not so sensible to insist everyone, despite not knowing what skills they do or don't have, does not have the necessary skills to work with them. It's not difficult, just need to know the issues/gotchas. There's EHT, soakage, leakage, and the principles of the interlock system. Otherwise it's just more electrical equipment, with its design quirks like the transformer.


NT