Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.

Could this be linked to the fact that I used it earlier to heat up an empty
pyrex dish (high setting for two minutes)? That worked perfectly and I've
done it before with no ill effects.

This is a Panasonic combi microwave/convenction oven about six years old.

Many thanks for any thoughts.

On Tuesday, April 30, 2013 8:41:55 PM UTC+1, Bert Coules wrote:

Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.

Could this be linked to the fact that I used it earlier to heat up an empty
pyrex dish (high setting for two minutes)?

no, that ceased to be a problem in the 1960s


NT

In article ,
"Bert Coules" writes:
Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.

Could this be linked to the fact that I used it earlier to heat up an empty
pyrex dish (high setting for two minutes)? That worked perfectly and I've
done it before with no ill effects.

This is a Panasonic combi microwave/convenction oven about six years old.

Many thanks for any thoughts.

Many microwave oven instructions warn of dire consequences if you use
them with nothing in them. Some time ago, we pondered on what happens
to the magnetron when you do this. My guess is that with nothing
absorbing the microwaves, they end up overheating the magnetron, and
either distort it until it stops resonating, or burn out the cathode
(which would be easy to continuity test, modulo all the dire warnings
about opening microwave cases, and the cathode is the very terminal
which will retain a very high (-ve) voltage on it, particularly if
the magnetron was no longer working). Some of them have a high voltage
fuse, which would be worth checking. The current rating of these is
usually a strange value, and the value is critical for safe operation,
as there's very little overcurrent available on the HV side to be able
to blow it.

I know someone who switched theirs on just to use the timer for
something else. It lasted about a week (don't know how many times
they did this during that period).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 30/04/2013 20:41, Bert Coules wrote:
Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.

Could this be linked to the fact that I used it earlier to heat up an
empty pyrex dish (high setting for two minutes)? That worked perfectly
and I've done it before with no ill effects.

This is a Panasonic combi microwave/convenction oven about six years old.

Many thanks for any thoughts.



More likely that there's something wrong with the interlock
micro-switches on the door - which prevent you from microwaving any part
of yourself by not letting it operate unless the door is firmly shut. If
these fail - or go out of adjustment - the thing won't operate, and may
even blow a fuse.

Does anything still work? Grill? Turntable? Light?
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On 30/04/2013 22:24, Roger Mills wrote:
On 30/04/2013 20:41, Bert Coules wrote:
Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.

Could this be linked to the fact that I used it earlier to heat up an
empty pyrex dish (high setting for two minutes)? That worked perfectly
and I've done it before with no ill effects.

This is a Panasonic combi microwave/convenction oven about six years old.

Many thanks for any thoughts.



More likely that there's something wrong with the interlock
micro-switches on the door - which prevent you from microwaving any part
of yourself by not letting it operate unless the door is firmly shut. If
these fail - or go out of adjustment - the thing won't operate, and may
even blow a fuse.

Does anything still work? Grill? Turntable? Light?

But if you try to start with the door open, normally nothing happens, no
light, no turntable. Could be that there are two switches of course, a
second one which just takes out the magnetron.

On Tue, 30 Apr 2013 20:41:55 +0100, "Bert Coules"
wrote:

Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.

Could this be linked to the fact that I used it earlier to heat up an empty
pyrex dish (high setting for two minutes)? That worked perfectly and I've
done it before with no ill effects.

This is a Panasonic combi microwave/convenction oven about six years old.

Many thanks for any thoughts.


Model number always helps but from your description of how it cuts out
after 20 seconds I can be pretty sure it's got an inverter and
associated protection circuitry.

With these the fault is usually the magnetron or the inverter PCB,
also the failure mode of the magnetron is often one of the ring
magnets gets cracked with the heat.

If it's not the magnetron it will probably be the inverter, probably
uneconomic to repair. When I was repairing them I was prepared to
repair to component level but could not find the IGBT's (transistors)
at a reasonable price.



--
Graham.

%Profound_observation%

On Tue, 30 Apr 2013 13:17:32 -0700 (PDT), wrote:

On Tuesday, April 30, 2013 8:41:55 PM UTC+1, Bert Coules wrote:

Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.

Could this be linked to the fact that I used it earlier to heat up an empty
pyrex dish (high setting for two minutes)?

no, that ceased to be a problem in the 1960s


NT

Can you explain that please?
I know Pyrex is not the same material as it used to be, but I can tell
you the Pyrex turntable in my microwave is insufficient as a dummy
load.



--
Graham.

%Profound_observation%

Roger Mills wrote:

More likely that there's something wrong with the interlock micro-switches
on the door...

That's an interesting notion: I'll check.

Does anything still work? Grill? Turntable? Light?

All of those. Fearing that something really fundamental might be amiss I
didn't check either the convention oven or the grill, but perhaps I should.

Thanks for the thoughts.

Graham wrote:

Model number always helps...

Ah yes, sorry. NN-A554W

...from your description of how it cuts out
after 20 seconds I can be pretty sure it's got an inverter and
associated protection circuitry.

It has. Well, the inverter certainly, since it proclaims the fact on the
front, and I assume the protection is there too.

If it's not the magnetron it will probably be the inverter, probably
uneconomic to repair.

Pity, if that is the trouble. The oven's far from new but until this
evening it was performing splendidly.

Many thanks, Graham.

On Tuesday, April 30, 2013 11:24:52 PM UTC+1, Graham. wrote:
On Tue, 30 Apr 2013 13:17:32 -0700 (PDT), wrote:
On Tuesday, April 30, 2013 8:41:55 PM UTC+1, Bert Coules wrote:

Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.
Could this be linked to the fact that I used it earlier to heat up an empty
pyrex dish (high setting for two minutes)?

no, that ceased to be a problem in the 1960s

Can you explain that please?
I know Pyrex is not the same material as it used to be, but I can tell
you the Pyrex turntable in my microwave is insufficient as a dummy
load.

Only early nukes were vulnerable to no load conditions.


NT

On Tuesday, April 30, 2013 10:33:18 PM UTC+1, newshound wrote:

But if you try to start with the door open, normally nothing happens, no
light, no turntable. Could be that there are two switches of course, a
second one which just takes out the magnetron.

Microwave interlock systems use 4 switches, resistor and fuse.


NT

Most Microwaves these days protect themselves from excessive feedback of the
signal. IE if I put too little into mine it will cut out when its had enough
so to speak, but I suppose it could have blown a fuse and monitoring its
output sees nothing after a while so just stops. Its very hard to say. Life
was far more predictable in the days of mechanical timers.

Brian

--
From the Sofa of Brian Gaff Reply address is active
wrote in message
...
On Tuesday, April 30, 2013 8:41:55 PM UTC+1, Bert Coules wrote:

Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.

Could this be linked to the fact that I used it earlier to heat up an
empty
pyrex dish (high setting for two minutes)?

no, that ceased to be a problem in the 1960s


NT

Bert Coules wrote:
Graham wrote:

Model number always helps...

Ah yes, sorry. NN-A554W

...from your description of how it cuts out
after 20 seconds I can be pretty sure it's got an inverter and
associated protection circuitry.

It has. Well, the inverter certainly, since it proclaims the fact on
the front, and I assume the protection is there too.

If it's not the magnetron it will probably be the inverter, probably
uneconomic to repair.

Pity, if that is the trouble. The oven's far from new but until this
evening it was performing splendidly.

Many thanks, Graham.


It could be a fuse, there are usually two fuses, one obvious, and a 5000
volt .75amp not so obvious,often hidden in a plastic tube near transformer.
this could be the culprit if the thing lights up but not cooks.
These fuses look like the normal glass fuse but longer.

On Tue, 30 Apr 2013 16:21:30 -0700 (PDT), wrote:

On Tuesday, April 30, 2013 11:24:52 PM UTC+1, Graham. wrote:
On Tue, 30 Apr 2013 13:17:32 -0700 (PDT), wrote:
On Tuesday, April 30, 2013 8:41:55 PM UTC+1, Bert Coules wrote:

Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.
Could this be linked to the fact that I used it earlier to heat up an empty
pyrex dish (high setting for two minutes)?

no, that ceased to be a problem in the 1960s

Can you explain that please?
I know Pyrex is not the same material as it used to be, but I can tell
you the Pyrex turntable in my microwave is insufficient as a dummy
load.

Only early nukes were vulnerable to no load conditions.


NT

I can't see why. Early microwave ovens had a substantial length of
wave-guide, and the radiation entered at the top of the cooking
cavity.
The wave guide doubled as an air duct for the fan so the magnetron was
more efficiently cooled.

--
Graham.

%Profound_observation%

On Thu, 02 May 2013 00:10:28 +1000, F Murtz
wrote:

Bert Coules wrote:
Graham wrote:

Model number always helps...

Ah yes, sorry. NN-A554W

...from your description of how it cuts out
after 20 seconds I can be pretty sure it's got an inverter and
associated protection circuitry.

It has. Well, the inverter certainly, since it proclaims the fact on
the front, and I assume the protection is there too.

If it's not the magnetron it will probably be the inverter, probably
uneconomic to repair.

Pity, if that is the trouble. The oven's far from new but until this
evening it was performing splendidly.

Many thanks, Graham.


It could be a fuse, there are usually two fuses, one obvious, and a 5000
volt .75amp not so obvious,often hidden in a plastic tube near transformer.
this could be the culprit if the thing lights up but not cooks.
These fuses look like the normal glass fuse but longer.

There won't be a conventional iron cored transformer.

--
Graham.

%Profound_observation%

On Tue, 30 Apr 2013 23:46:29 +0100, "Bert Coules"
wrote:

Graham wrote:

Model number always helps...

Ah yes, sorry. NN-A554W

...from your description of how it cuts out
after 20 seconds I can be pretty sure it's got an inverter and
associated protection circuitry.

It has. Well, the inverter certainly, since it proclaims the fact on the
front, and I assume the protection is there too.

If it's not the magnetron it will probably be the inverter, probably
uneconomic to repair.

Pity, if that is the trouble. The oven's far from new but until this
evening it was performing splendidly.

Many thanks, Graham.


If you are up to opening it I can show you how you can tell if it's
the magnetron that is faulty. Basically you pull off two wires and see
if it doesn't cut out after 20 seconds the inverter is OK.

You could then get a cheap generic magnetron or even salvage one out
of a scrap unit, although strictly speaking you are supposed to use
the correct one which is a lot more expensive.



--
Graham.

%Profound_observation%

On Wednesday, May 1, 2013 9:23:41 PM UTC+1, Graham. wrote:
On Tue, 30 Apr 2013 16:21:30 -0700 (PDT), wrote:


Only early nukes were vulnerable to no load conditions.

I can't see why. Early microwave ovens had a substantial length of
wave-guide, and the radiation entered at the top of the cooking
cavity.
The wave guide doubled as an air duct for the fan so the magnetron was
more efficiently cooled.

I don't know for sure what changed since then, but I'd presume its 2 things:
a) enough thermal margin that the magnetron doesnt die when power is reflected back to it
b) waveguide that doesnt arc when reflected power is also added


NT

Graham. wrote:
On Thu, 02 May 2013 00:10:28 +1000, F Murtz
wrote:

Bert Coules wrote:
Graham wrote:

Model number always helps...

Ah yes, sorry. NN-A554W

...from your description of how it cuts out
after 20 seconds I can be pretty sure it's got an inverter and
associated protection circuitry.

It has. Well, the inverter certainly, since it proclaims the fact on
the front, and I assume the protection is there too.

If it's not the magnetron it will probably be the inverter, probably
uneconomic to repair.

Pity, if that is the trouble. The oven's far from new but until this
evening it was performing splendidly.

Many thanks, Graham.


It could be a fuse, there are usually two fuses, one obvious, and a 5000
volt .75amp not so obvious,often hidden in a plastic tube near transformer.
this could be the culprit if the thing lights up but not cooks.
These fuses look like the normal glass fuse but longer.

There won't be a conventional iron cored transformer.

Is on mine,dont know about his model

F Murtz wrote:
Graham. wrote:
On Thu, 02 May 2013 00:10:28 +1000, F Murtz
wrote:

Bert Coules wrote:
Graham wrote:

Model number always helps...

Ah yes, sorry. NN-A554W

...from your description of how it cuts out
after 20 seconds I can be pretty sure it's got an inverter and
associated protection circuitry.

It has. Well, the inverter certainly, since it proclaims the fact on
the front, and I assume the protection is there too.

If it's not the magnetron it will probably be the inverter, probably
uneconomic to repair.

Pity, if that is the trouble. The oven's far from new but until this
evening it was performing splendidly.

Many thanks, Graham.


It could be a fuse, there are usually two fuses, one obvious, and a 5000
volt .75amp not so obvious,often hidden in a plastic tube near
transformer.
this could be the culprit if the thing lights up but not cooks.
These fuses look like the normal glass fuse but longer.

There won't be a conventional iron cored transformer.

Is on mine,dont know about his model
OOPS it seems his is an inverter type.

It could be a fuse, there are usually two fuses, one obvious, and a 5000
volt .75amp not so obvious,often hidden in a plastic tube near
transformer.
this could be the culprit if the thing lights up but not cooks.
These fuses look like the normal glass fuse but longer.

There won't be a conventional iron cored transformer.

Is on mine,dont know about his model
OOPS it seems his is an inverter type.

They also don't have the big oil-filled capacitor, so they are
probably safer to work on when unplugged.


--
Graham.

%Profound_observation%

I've now had a chance to test the grill and the convection oven, and both
are still working. So the inverter does perhaps seem the likely culprit.

I have a panasonic nn a554w microwave. The turntable has stopped turning on all cooking options.

wrote:
I have a panasonic nn a554w microwave. The turntable has stopped turning on all cooking options.

Burned out motor or stripped gears or what ever switches it on is
buggered. You will have to do some diy to find out which!

On Sat, 20 Feb 2016 08:47:52 -0800 (PST),
wrote:

I have a panasonic nn a554w microwave. The turntable has stopped turning on all cooking options.
Turntable motor probebly.

No need to remove the cover, access is provided on the underside of
the machine.

Unplug, Set it on its side, and use a rat-tail file to remove the
knock-out hatch.

It should be obvious how to proceed from there, The motors operate at
mains voltage and usually differ between machine makes/models only by
spindle length, so you may be in luck if you have a scrap machine as a
parts donor.

There will be some lugs and screw holes to refit the hatch. They may
have even parked the self-tapper(s) in the hole(s)


--

Graham.

%Profound_observation%

On Wednesday, 1 May 2013 21:23:41 UTC+1, Graham. wrote:
On Tue, 30 Apr 2013 16:21:30 -0700 (PDT), wrote:
On Tuesday, April 30, 2013 11:24:52 PM UTC+1, Graham. wrote:
On Tue, 30 Apr 2013 13:17:32 -0700 (PDT), wrote:
On Tuesday, April 30, 2013 8:41:55 PM UTC+1, Bert Coules wrote:

Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.
Could this be linked to the fact that I used it earlier to heat up an empty
pyrex dish (high setting for two minutes)?

no, that ceased to be a problem in the 1960s

Can you explain that please?
I know Pyrex is not the same material as it used to be, but I can tell
you the Pyrex turntable in my microwave is insufficient as a dummy
load.

Only early nukes were vulnerable to no load conditions.

I can't see why. Early microwave ovens had a substantial length of
wave-guide, and the radiation entered at the top of the cooking
cavity.
The wave guide doubled as an air duct for the fan so the magnetron was
more efficiently cooled.

It was 3 yrs ago, but fwiw early nukes were water cooled


NT

On 20/02/2016 18:18, Graham. wrote:

It should be obvious how to proceed from there, The motors operate at
mains voltage and usually differ between machine makes/models only by
spindle length, so you may be in luck if you have a scrap machine as a
parts donor.


£7.50 from CPC
http://cpc.farnell.com/europart/75-u...ble/dp/WG22157


--
mailto: news {at} admac {dot] myzen {dot} co {dot} uk

wrote in message
...

I have a panasonic nn a554w microwave. The
turntable has stopped turning on all cooking options.

What turns the turntable is ****ed, or its
jammed if you can't turn it with your hand.

Do you use the alternative functions at all or like many things it sounded good at the time? (like 95% of cooker timers) if you only ever microwave with it I'd suggest a new el-cheapo supermarket special might be far the simplest solution.

Do some options result in a non rotating turntable on purpose? If so you
might just have a relay issue.
brain

--
From the Sofa of Brian Gaff Reply address is active
Remember, if you don't like where I post
or what I say, you don't have to
read my posts! :-)
wrote in message
...
I have a panasonic nn a554w microwave. The turntable has stopped turning on
all cooking options.

On Tuesday, April 30, 2013 at 8:41:55 PM UTC+1, Bert Coules wrote:
Working perfectly this afternoon, tonight it runs for twenty seconds and
then switches the cooking process off (without the usual end-of-sequence
beeping) and there's no evidence that the food has been heated even
slightly.

Could this be linked to the fact that I used it earlier to heat up an empty
pyrex dish (high setting for two minutes)? That worked perfectly and I've
done it before with no ill effects.

This is a Panasonic combi microwave/convenction oven about six years old.

Many thanks for any thoughts.

Our Panasonic stopped working. It turned out to be the magnetron which had overheated and cracked a magnet. A replacement magnetron fixed it.
The reason for the overheating was that the narrow channels through the magnetron heat sink had become completely blocked with dust.
Now, when I remember, I take the covers off and vacuum out those channels.
I feel that some kind of easily replaceable air filter in the airflow to the magnetron would be a big improvement to the design - together with some warning indicator to tell when to replace.

Edgar,

I'm grateful for your thoughts. Did you realise that you're replying to a
post I made nearly three years ago?

Bert

On Monday, February 22, 2016 at 1:50:19 PM UTC, Bert Coules wrote:
Edgar,

I'm grateful for your thoughts. Did you realise that you're replying to a
post I made nearly three years ago?

Bert

Discovering Google Groups. Sorry.

However I think the idea of cleaning out the heat sink is still useful.

Edgar

Edgar,

However I think the idea of cleaning out the heat sink is still useful.

Unfortunately, I no longer own the oven in question. And I'm afraid I can't
now remember if I did manage to fix it, or if I did, how. But thanks again
for your advice.

Bert

Thanks for the suggestion...I m facing a similar issue... Microwave used for twenty minutes on full power to defrost frozen spaghetti (probably shouldn't have done that) since then microwave cuts out after 30-40 seconds although once or twice a day it still goes on without cutting but doesn't really heat the food, sort of warms it up... I guess magnetron is on the blink...

On Friday, 1 September 2017 13:19:58 UTC+1, wrote:

Thanks for the suggestion...I m facing a similar issue... Microwave used for twenty minutes on full power to defrost frozen spaghetti (probably shouldn't have done that) since then microwave cuts out after 30-40 seconds although once or twice a day it still goes on without cutting but doesn't really heat the food, sort of warms it up... I guess magnetron is on the blink....

Most likely a partially shorted transformer. A damaged thermal cutout is not impossible.


NT