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What might be wrong with my microwave?
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Bert Coules
Apr 30, 2013, 3:41:55 PM4/30/13
to
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.
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.
meow...@care2.com
Apr 30, 2013, 4:17:32 PM4/30/13
to
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
> 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)?
NT
Andrew Gabriel
Apr 30, 2013, 4:21:09 PM4/30/13
to
In article <U_GdnSrbIesYgx3M...@brightview.co.uk>,
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]
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]
Roger Mills
Apr 30, 2013, 5:24:20 PM4/30/13
to
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.
newshound
Apr 30, 2013, 5:33:18 PM4/30/13
to
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
> 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?
light, no turntable. Could be that there are two switches of course, a
second one which just takes out the magnetron.
Graham.
Apr 30, 2013, 6:17:54 PM4/30/13
to
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%
Graham.
Apr 30, 2013, 6:24:52 PM4/30/13
to
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%
Bert Coules
Apr 30, 2013, 6:41:19 PM4/30/13
to
Roger Mills wrote:
> More likely that there's something wrong with the interlock micro-switches
> on the door...
> More likely that there's something wrong with the interlock micro-switches
That's an interesting notion: I'll check.
> Does anything still work? Grill? Turntable? Light?
didn't check either the convention oven or the grill, but perhaps I should.
Thanks for the thoughts.
Bert Coules
Apr 30, 2013, 6:46:29 PM4/30/13
to
Graham wrote:
> Model number always helps...
Ah yes, sorry. NN-A554W
> ...from your description of how it cuts out
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.
> 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
> associated protection circuitry.
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.
evening it was performing splendidly.
Many thanks, Graham.
meow...@care2.com
Apr 30, 2013, 7:21:30 PM4/30/13
to
On Tuesday, April 30, 2013 11:24:52 PM UTC+1, Graham. wrote:
> On Tue, 30 Apr 2013 13:17:32 -0700 (PDT), meow...@care2.com 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
> On Tue, 30 Apr 2013 13:17:32 -0700 (PDT), meow...@care2.com 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 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.
NT
meow...@care2.com
Apr 30, 2013, 7:23:25 PM4/30/13
to
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.
> 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.
NT
Brian Gaff
May 1, 2013, 3:28:03 AM5/1/13
to
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
<meow...@care2.com> wrote in message
news:c6436c6e-f0c7-4dd3...@googlegroups.com...
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
<meow...@care2.com> wrote in message
news:c6436c6e-f0c7-4dd3...@googlegroups.com...
F Murtz
May 1, 2013, 10:10:28 AM5/1/13
to
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.
Graham.
May 1, 2013, 4:23:41 PM5/1/13
to
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%
Graham.
May 1, 2013, 4:27:18 PM5/1/13
to
On Thu, 02 May 2013 00:10:28 +1000, F Murtz <hag...@hotmail.com>
wrote:
There won't be a conventional iron cored transformer.
--
Graham.
%Profound_observation%
wrote:
--
Graham.
%Profound_observation%
Graham.
May 1, 2013, 5:07:16 PM5/1/13
to
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%
meow...@care2.com
May 1, 2013, 8:02:37 PM5/1/13
to
On Wednesday, May 1, 2013 9:23:41 PM UTC+1, Graham. wrote:
> On Tue, 30 Apr 2013 16:21:30 -0700 (PDT), meow...@care2.com wrote:
> >Only early nukes were vulnerable to no load conditions.
> On Tue, 30 Apr 2013 16:21:30 -0700 (PDT), meow...@care2.com 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:
> 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.
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
F Murtz
May 2, 2013, 9:19:56 AM5/2/13
to
F Murtz
May 2, 2013, 9:35:44 AM5/2/13
to
Graham.
May 3, 2013, 4:16:48 AM5/3/13
to
>>>>>
>>>> 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.
probably safer to work on when unplugged.
--
Graham.
%Profound_observation%
Bert Coules
May 8, 2013, 5:53:26 AM5/8/13
to
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.
are still working. So the inverter does perhaps seem the likely culprit.
alphas...@googlemail.com
Feb 20, 2016, 11:48:02 AM2/20/16
to
I have a panasonic nn a554w microwave. The turntable has stopped turning on all cooking options.
Bob Minchin
Feb 20, 2016, 12:49:37 PM2/20/16
to
alphas...@googlemail.com 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
> I have a panasonic nn a554w microwave. The turntable has stopped turning on all cooking options.
>
buggered. You will have to do some diy to find out which!
Graham.
Feb 20, 2016, 1:18:47 PM2/20/16
to
On Sat, 20 Feb 2016 08:47:52 -0800 (PST), alphas...@googlemail.com
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%
wrote:
>I have a panasonic nn a554w microwave. The turntable has stopped turning on all cooking options.
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%
tabb...@gmail.com
Feb 20, 2016, 3:15:37 PM2/20/16
to
On Wednesday, 1 May 2013 21:23:41 UTC+1, Graham. wrote:
> On Tue, 30 Apr 2013 16:21:30 -0700 (PDT), meow...@care2.com wrote:
> >On Tuesday, April 30, 2013 11:24:52 PM UTC+1, Graham. wrote:
> >> On Tue, 30 Apr 2013 13:17:32 -0700 (PDT), meow...@care2.com 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.
> On Tue, 30 Apr 2013 16:21:30 -0700 (PDT), meow...@care2.com wrote:
> >On Tuesday, April 30, 2013 11:24:52 PM UTC+1, Graham. wrote:
> >> On Tue, 30 Apr 2013 13:17:32 -0700 (PDT), meow...@care2.com 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
> 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.
NT
alan_m
Feb 20, 2016, 3:49:05 PM2/20/16
to
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
> 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.
>
http://cpc.farnell.com/europart/75-un-13/universal-microwave-turntable/dp/WG22157
--
mailto: news {at} admac {dot] myzen {dot} co {dot} uk
Rod Speed
Feb 20, 2016, 10:54:52 PM2/20/16
to
<alphas...@googlemail.com> wrote in message
news:dadbd39d-bf44-4faa...@googlegroups.com...
> I have a panasonic nn a554w microwave. The
> turntable has stopped turning on all cooking options.
jammed if you can't turn it with your hand.
johnje...@gmail.com
Feb 21, 2016, 4:27:16 AM2/21/16
to
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.
Brian-Gaff
Feb 21, 2016, 5:59:02 AM2/21/16
to
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! :-)
might just have a relay issue.
brain
--
From the Sofa of Brian Gaff Reply address is active
or what I say, you don't have to
read my posts! :-)
Edgar
Feb 21, 2016, 6:55:43 AM2/21/16
to
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
> 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.
> done it before with no ill effects.
>
> This is a Panasonic combi microwave/convenction oven about six years old.
>
> Many thanks for any thoughts.
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.
Bert Coules
Feb 22, 2016, 8:50:19 AM2/22/16
to
Edgar,
I'm grateful for your thoughts. Did you realise that you're replying to a
post I made nearly three years ago?
Bert
I'm grateful for your thoughts. Did you realise that you're replying to a
post I made nearly three years ago?
Bert
edgari...@gmail.com
Feb 24, 2016, 2:54:58 PM2/24/16
to
However I think the idea of cleaning out the heat sink is still useful.
Edgar
Bert Coules
Feb 25, 2016, 6:33:30 AM2/25/16
to
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
> However I think the idea of cleaning out the heat sink is still useful.
now remember if I did manage to fix it, or if I did, how. But thanks again
for your advice.
Bert
gswar...@gmail.com
Sep 1, 2017, 8:19:58 AM9/1/17
to
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...
tabb...@gmail.com
Sep 3, 2017, 4:54:49 AM9/3/17
to
On Friday, 1 September 2017 13:19:58 UTC+1, gswar...@gmail.com 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.
> 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...
NT
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