Inverter microwave ovens - reliable?

[Franc Zabkar]

My brother's Panasonic model NN-ST756W inverter microwave oven failed
after one year, just out of warranty. I found a short circuited HV
diode, D702, UX-C2B. The associated 8200pF 3kV capacitor appears OK,
as do the inverter transistors.

The inverter PCB (240V version) is similar to the one in these service
manuals:

http://www.eletrodomesticosforum.com/downloads/microondas/Panasonic_NN-G62BH.pdf
http://rc5.ru/upload/panasonic_mw_NN-C2000_(MWO).pdf

Here are several exploded views and parts lists:

http://www.prime-electronics.com.au/trade/cgi-bin/display.pl?brand=PANASONIC&product=MICROWAVE&model=NNST756W&view=OVEN%20ASSY.jpg
http://preview.tinyurl.com/bre9kh

http://www.prime-electronics.com.au/trade/PRICEANDAVAIL/frametest.asp?Model1=NNST756W&Submit=Search&search=search&Model=NNST756W&Model1=NNST756W&Submit=Search&search=search&BRAND=PANASONIC&Model1=NNST756W&Submit=Search&search=search&PRODUCT=MICROWAVE
http://preview.tinyurl.com/ahr8s8

I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types. They seem to be overly
complicated for what they do. I understand that they cook more evenly
in low power modes as a consequence of not having to pulse on and off
like conventional microwaves, but I'd rather not pay a reliability
penalty for this feature. BTW, once the microwave is sitting on my
bench top, the extra weight of a traditional mains transformer is of
no consequence.

The Microwave Oven Repair FAQ appears to bear me out:
http://www.repairfaq.org/REPAIR/F_micfaq6.html#MICFAQ_019

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[GregS]

In article <c51rq45drq5m4e3soblc1lq7eadnen1h40@4ax.com>, fzabkar@iinternode.on.net wrote:

My brother's Panasonic model NN-ST756W inverter microwave oven failed
after one year, just out of warranty. I found a short circuited HV
diode, D702, UX-C2B. The associated 8200pF 3kV capacitor appears OK,
as do the inverter transistors.

The inverter PCB (240V version) is similar to the one in these service
manuals:

http://www.eletrodomesticosforum.com/downloads/microondas/Panasonic_NN-G62BH.pd
f
http://rc5.ru/upload/panasonic_mw_NN-C2000_(MWO).pdf

Here are several exploded views and parts lists:

http://www.prime-electronics.com.au/trade/cgi-bin/display.pl?brand=PANASONIC&pr
oduct=MICROWAVE&model=NNST756W&view=OVEN%20ASSY.jpg
http://preview.tinyurl.com/bre9kh

http://www.prime-electronics.com.au/trade/PRICEANDAVAIL/frametest.asp?Model1=NN
ST756W&Submit=Search&search=search&Model=NNST756W&Model1=NNST756W&Submit=Search
&search=search&BRAND=PANASONIC&Model1=NNST756W&Submit=Search&search=search&PROD
UCT=MICROWAVE
http://preview.tinyurl.com/ahr8s8

I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types. They seem to be overly
complicated for what they do. I understand that they cook more evenly
in low power modes as a consequence of not having to pulse on and off
like conventional microwaves, but I'd rather not pay a reliability
penalty for this feature. BTW, once the microwave is sitting on my
bench top, the extra weight of a traditional mains transformer is of
no consequence.

The Microwave Oven Repair FAQ appears to bear me out:
http://www.repairfaq.org/REPAIR/F_micfaq6.html#MICFAQ_019

- Franc Zabkar

I didn't know much about it. I bought one maybe 3 years ago. Small lightweight,
and the most powerfull one I have ever had. I use it everyday. The only problem, the light
does not come on when you open the door. My brother uses one in a resturant,
and they have failed after much use. That one the commercial job, costs a lot
more. Like I said, it small, powerfull, and cheap. My Sears GE microwave is
big, not nearly as powerfull, also has turbo oven, but I use the Panasonic
to heat fast. By other brother has a Samsung which has failed. Replaced
diode and found the transformer is bad. After two months still waiting for transformer.

greg

 

[Joel Koltner]

"Franc Zabkar" <fzabkar@iinternode.on.net> wrote in message
news:c51rq45drq5m4e3soblc1lq7eadnen1h40@4ax.com...

I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types.

Since they're a relatively new technology (at least at the consumer level), my
suspicion would be that, yeah, they are a bit less reliable.

BTW, once the microwave is sitting on my
bench top, the extra weight of a traditional mains transformer is of
no consequence.

There's also a bit of savings in lower freight costs from the lower weight.
And smaller people (women in particular) tend to put some emphasis on the
weight of their kitchen appliances, even if (as you point out) it's often
completely irrelevant once you get the thing up on the counter at home.

 

[hr(bob) hofmann@att.net]

On Mar 3, 2:47 pm, zekfr...@zekfrivolous.com (GregS) wrote:

In article <c51rq45drq5m4e3soblc1lq7eadnen1...@4ax.com>, fzab...@iinternode.on.net wrote:
My brother's Panasonic model NN-ST756W inverter microwave oven failed
after one year, just out of warranty. I found a short circuited HV
diode, D702, UX-C2B. The associated 8200pF 3kV capacitor appears OK,
as do the inverter transistors.

The inverter PCB (240V version) is similar to the one in these service
manuals:

http://www.eletrodomesticosforum.com/downloads/microondas/Panasonic_N...
f
http://rc5.ru/upload/panasonic_mw_NN-C2000_(MWO).pdf

Here are several exploded views and parts lists:

http://www.prime-electronics.com.au/trade/cgi-bin/display.pl?brand=PA....
oduct=MICROWAVE&model=NNST756W&view=OVEN%20ASSY.jpg
http://preview.tinyurl.com/bre9kh

http://www.prime-electronics.com.au/trade/PRICEANDAVAIL/frametest.asp...
ST756W&Submit=Search&search=search&Model=NNST756W&Model1=NNST756W&Submit=S­earch
&search=search&BRAND=PANASONIC&Model1=NNST756W&Submit=Search&search=search­&PROD
UCT=MICROWAVE
http://preview.tinyurl.com/ahr8s8

I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types. They seem to be overly
complicated for what they do. I understand that they cook more evenly
in low power modes as a consequence of not having to pulse on and off
like conventional microwaves, but I'd rather not pay a reliability
penalty for this feature. BTW, once the microwave is sitting on my
bench top, the extra weight of a traditional mains transformer is of
no consequence.

The Microwave Oven Repair FAQ appears to bear me out:
http://www.repairfaq.org/REPAIR/F_micfaq6.html#MICFAQ_019

- Franc Zabkar

I didn't know much about it. I bought one maybe 3 years ago. Small lightweight,
and the most powerfull one I have ever had. I use it everyday. The only problem, the light
does not come on when you open the door. My brother uses one in a resturant,
and they have failed after much use. That one the commercial job, costs a lot
more. Like I said, it small, powerfull, and cheap. My Sears GE microwave is
big, not nearly as powerfull, also has turbo oven, but I use the Panasonic
to heat fast. By other brother has a Samsung which has failed. Replaced
diode and found the transformer is bad. After two months still waiting for transformer.

greg- Hide quoted text -

- Show quoted text -

Maybe the reason the light does not come on is because it is burned
out.

 

[Jim Yanik]

"Joel Koltner" <zapwireDASHgroups@yahoo.com> wrote in
news:v1hrl.13379$9j5.7930@en-nntp-01.dc1.easynews.com:

"Franc Zabkar" <fzabkar@iinternode.on.net> wrote in message
news:c51rq45drq5m4e3soblc1lq7eadnen1h40@4ax.com...
I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types.

Since they're a relatively new technology (at least at the consumer
level), my suspicion would be that, yeah, they are a bit less
reliable.

BTW, once the microwave is sitting on my
bench top, the extra weight of a traditional mains transformer is of
no consequence.

There's also a bit of savings in lower freight costs from the lower
weight.

the savings is in not having to build an expensive,big transformer.
all that copper is expensive,too.

And smaller people (women in particular) tend to put some
emphasis on the weight of their kitchen appliances, even if (as you
point out) it's often completely irrelevant once you get the thing up
on the counter at home.

transformers,being far less complicated,are more reliable.
Inverters have a lot more components,particularly electrolytic caps,that
increase the odds of failure.
Many electrolytics are only rated for 3000 hrs or so of operation.
and it seems that surface-mount electrolytic caps are even less long-
lasting.

--
Jim Yanik
jyanik
at
kua.net

 

[Samuel M. Goldwasser]

Franc Zabkar <fzabkar@iinternode.on.net> writes:

My brother's Panasonic model NN-ST756W inverter microwave oven failed
after one year, just out of warranty. I found a short circuited HV
diode, D702, UX-C2B. The associated 8200pF 3kV capacitor appears OK,
as do the inverter transistors.

The inverter PCB (240V version) is similar to the one in these service
manuals:

http://www.eletrodomesticosforum.com/downloads/microondas/Panasonic_NN-G62BH.pdf
http://rc5.ru/upload/panasonic_mw_NN-C2000_(MWO).pdf

Here are several exploded views and parts lists:

http://www.prime-electronics.com.au/trade/cgi-bin/display.pl?brand=PANASONIC&product=MICROWAVE&model=NNST756W&view=OVEN%20ASSY.jpg
http://preview.tinyurl.com/bre9kh

http://www.prime-electronics.com.au/trade/PRICEANDAVAIL/frametest.asp?Model1=NNST756W&Submit=Search&search=search&Model=NNST756W&Model1=NNST756W&Submit=Search&search=search&BRAND=PANASONIC&Model1=NNST756W&Submit=Search&search=search&PRODUCT=MICROWAVE
http://preview.tinyurl.com/ahr8s8

I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types. They seem to be overly
complicated for what they do. I understand that they cook more evenly
in low power modes as a consequence of not having to pulse on and off
like conventional microwaves, but I'd rather not pay a reliability
penalty for this feature. BTW, once the microwave is sitting on my
bench top, the extra weight of a traditional mains transformer is of
no consequence.

The Microwave Oven Repair FAQ appears to bear me out:
http://www.repairfaq.org/REPAIR/F_micfaq6.html#MICFAQ_019

Aside from the reliability issues which have been addressed in other
replies, it's possible that the HV diode died for reasons unrelated
to the inverter.

What does the oven do when you go to "cook". If nothing at all, then
there are almost certainly other bad parts, a fuse at the very least.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[Mike WB2MEP]

On Mar 3, 2:28 pm, Franc Zabkar <fzab...@iinternode.on.net> wrote:

My brother's Panasonic model NN-ST756W inverter microwave oven failed
after one year, just out of warranty. I found a short circuited HV
diode, D702, UX-C2B. The associated 8200pF 3kV capacitor appears OK,
as do the inverter transistors.

The inverter PCB (240V version) is similar to the one in these service
manuals:

http://www.eletrodomesticosforum.com/downloads/microondas/Panasonic_N...http://rc5.ru/upload/panasonic_mw_NN-C2000_(MWO).pdf

Here are several exploded views and parts lists:

http://www.prime-electronics.com.au/trade/cgi-bin/display.pl?brand=PA....http://preview.tinyurl.com/bre9kh

http://www.prime-electronics.com.au/trade/PRICEANDAVAIL/frametest.asp...http://preview.tinyurl.com/ahr8s8

I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types. They seem to be overly
complicated for what they do. I understand that they cook more evenly
in low power modes as a consequence of not having to pulse on and off
like conventional microwaves, but I'd rather not pay a reliability
penalty for this feature. BTW, once the microwave is sitting on my
bench top, the extra weight of a traditional mains transformer is of
no consequence.

The Microwave Oven Repair FAQ appears to bear me out:http://www.repairfaq..org/REPAIR/F_micfaq6.html#MICFAQ_019

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Franc,

I don't think they're as reliable as conventional transformer/diode/
cap
power supplies. "Inverter" is just a switching power supply that
steps
up the voltage, and consumer-grade SMPS in a variety of products have
a
rather high failure rate.

There were several threads on SER a few years ago when Panasonic
first came out with the Inverter oves, about failures of the Inverter
circuit. At that time, Panasonic wouldn't sell replacement parts for
the Inverter power supply, or even provide a part number for the
switching trasistors that were failing. You had to replace the whole
power supply, which cost almost as much as a new oven.

The service manual for the NN-C2000 you linked to does have a parts
list for the Inverter board, so maybe they are considered repairable
now.

3 or 4 years ago, we needed a new microwave for the break room at
work.
Somebody donated an old (1984) Panasonic with a transformer power
supply,
and shortly thereafter a fancy new stainless-steel Panasonic Inverter
microwave was purchased. The two were used side-by-side for just over
a
year, then one day I came in and saw the Inverter oven set outside for
trash pickup.

So, I would definitely avoid the Inverter microwaves. Other
manufacturers
may be using switching power supplies, just not using the "Inverter"
name.
Last time I checked, most of the microwaves were still using
transformer
power supplies, but once the cost of a switching supply becomes less
than
a conventional supply, I would expect most of them to change over to
SMPS.

When you go into the store, just lift up the right side of each
microwave
on display, and buy the heaviest one.

Mike
WB2MEP

 

[Franc Zabkar]

On 03 Mar 2009 19:34:24 -0500, sam@repairfaq.org (Samuel M.
Goldwasser) put finger to keyboard and composed:

Aside from the reliability issues which have been addressed in other
replies, it's possible that the HV diode died for reasons unrelated
to the inverter.

I'm not sure where to look except for the magnetron.

Page 20 of the following service manual has a detailed circuit diagram
of the inverter:
http://www.eletrodomesticosforum.com/downloads/microondas/Panasonic_NN-G62BH.pdf

Page 42 of this manual has a block diagram of the controller chip:
http://rc5.ru/upload/panasonic_mw_NN-C2000_(MWO).pdf

What does the oven do when you go to "cook". If nothing at all, then
there are almost certainly other bad parts, a fuse at the very least.

I didn't test it in case something else broke, but my brother tells me
that everything appears to work except for the actual heating. That
is, the control panel works, the turntable turns, and the fan spins. A
shorted HV diode (there are two in a voltage doubler arrangement)
would mean that one of the 8200pF caps is now connected directly
across the secondary winding. I expect this would overload the
transformer and presumably the inverter would sense this fault
condition via the current transformer in the primary circuit. I'm told
that the oven shuts down after a time. Anyway I've ordered the diode
and I'll report back once I've tried it.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[GregS]

In article <037dc1a9-ba29-4109-be9a-a234e37584b9@o2g2000prl.googlegroups.com>, "hr(bob) hofmann@att.net" <hrhofmann@att.net> wrote:

On Mar 3, 2:47=A0pm, zekfr...@zekfrivolous.com (GregS) wrote:
In article <c51rq45drq5m4e3soblc1lq7eadnen1...@4ax.com>, fzab...@iinterno=
de.on.net wrote:
My brother's Panasonic model NN-ST756W inverter microwave oven failed
after one year, just out of warranty. I found a short circuited HV
diode, D702, UX-C2B. The associated 8200pF 3kV capacitor appears OK,
as do the inverter transistors.

The inverter PCB (240V version) is similar to the one in these service
manuals:

http://www.eletrodomesticosforum.com/downloads/microondas/Panasonic_N...
f
http://rc5.ru/upload/panasonic_mw_NN-C2000_(MWO).pdf

Here are several exploded views and parts lists:

http://www.prime-electronics.com.au/trade/cgi-bin/display.pl?brand=3DPA.=
...
oduct=3DMICROWAVE&model=3DNNST756W&view=3DOVEN%20ASSY.jpg
http://preview.tinyurl.com/bre9kh

http://www.prime-electronics.com.au/trade/PRICEANDAVAIL/frametest.asp...
ST756W&Submit=3DSearch&search=3Dsearch&Model=3DNNST756W&Model1=3DNNST756=
W&Submit=3DS=ADearch
&search=3Dsearch&BRAND=3DPANASONIC&Model1=3DNNST756W&Submit=3DSearch&sea=
rch=3Dsearch=AD&PROD
UCT=3DMICROWAVE
http://preview.tinyurl.com/ahr8s8

I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types. They seem to be overly
complicated for what they do. I understand that they cook more evenly
in low power modes as a consequence of not having to pulse on and off
like conventional microwaves, but I'd rather not pay a reliability
penalty for this feature. BTW, once the microwave is sitting on my
bench top, the extra weight of a traditional mains transformer is of
no consequence.

The Microwave Oven Repair FAQ appears to bear me out:
http://www.repairfaq.org/REPAIR/F_micfaq6.html#MICFAQ_019

- Franc Zabkar

I didn't know much about it. I bought one maybe 3 years ago. Small lightw=
eight,
and the most powerfull one I have ever had. I use it everyday. The only p=
roblem, the light
does not come on when you open the door. My brother uses one in a restura=
nt,
and they have failed after much use. That one the commercial job, costs a=
lot
more. Like I said, it small, powerfull, and cheap. My Sears GE microwave =
is
big, not nearly as powerfull, also has turbo oven, but I use the Panasoni=
c
to heat fast. By other brother has a Samsung which has failed. Replaced
diode and found the transformer is bad. After two months still waiting fo=
r transformer.

greg- Hide quoted text -

- Show quoted text -

Maybe the reason the light does not come on is because it is burned
out.

The light comes on when its cooking. I usually carrry a flashlight so I can see the
condition of the food.

greg

 

[jakdedert]

GregS wrote:
<snip>

- Show quoted text -
Maybe the reason the light does not come on is because it is burned
out.

The light comes on when its cooking. I usually carrry a flashlight so I can see the
condition of the food.

That seems kind of obvious: door switch...probably gunked up with food

residue.

jak
> greg

 

[GregS]

In article <B4wrl.11473$b9.7677@bignews6.bellsouth.net>, jakdedert <jakdedert@bellsouth.net> wrote:

GregS wrote:
snip

- Show quoted text -
Maybe the reason the light does not come on is because it is burned
out.

The light comes on when its cooking. I usually carrry a flashlight so I can
see the
condition of the food.

That seems kind of obvious: door switch...probably gunked up with food
residue.

jak
greg

It never worked. I don't see any reason to not believe thats the way its
designed. I need to hear from those who have these.
But, one day I'll open er up and change it.

I remember way back on an old Norelco microwave, the controller
failed, so I got out the old mechanical timer just like the one
on my first Heathkit microwave. I can't stress how this simple and easy
to use feature is missing on todays ovens. My father loved it.
I think on better models they used aother timer to cycle
the defrost. Those older models had at least 3 fail safe
microswitches on them, but the switch took the full current.
I'm sure in a fail safe mode, at least one microswitch in
ALL microwaves take the full current.

greg

 

[Franc Zabkar]

On Tue, 3 Mar 2009 15:57:41 -0800 (PST), Mike WB2MEP
<michael.w.appenzeller@lmco.com> put finger to keyboard and composed:

On Mar 3, 2:28 pm, Franc Zabkar <fzab...@iinternode.on.net> wrote:

I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types.

There were several threads on SER a few years ago when Panasonic
first came out with the Inverter oves, about failures of the Inverter
circuit. At that time, Panasonic wouldn't sell replacement parts for
the Inverter power supply, or even provide a part number for the
switching trasistors that were failing. You had to replace the whole
power supply, which cost almost as much as a new oven.

The service manual for the NN-C2000 you linked to does have a parts
list for the Inverter board, so maybe they are considered repairable
now.

The transistors are now offered as "A691E4V10GP Transistor Kit Series
2".

Here are the datasheets for the GT30J322 (75W) and GT60M303 (170W)
IGBTs:
http://www.toshiba.com/taec/components2/Datasheet_Sync//361/4133.pdf
http://www.toshiba.com/taec/components2/Datasheet_Sync//361/4169.pdf

The oven has a rated output of 1100W. If the SMPS has an efficiency of
90%, then I expect that the transistors would be dissipating around
100W between them, although the mass of the heatsink appears
relatively small for such a high heat load.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[David Lesher]

jakdedert <jakdedert@bellsouth.net> writes:

The light comes on when its cooking. I usually carrry a flashlight so I can see the
condition of the food.

That seems kind of obvious: door switch...probably gunked up with food
residue.

My sister had one like that; light on during cook -- no light with the
door open. Dumb design.

I added a relay to solve the issue and was the big hero...


--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

 

[Franc Zabkar]

On Wed, 04 Mar 2009 16:10:38 +1100, Franc Zabkar
<fzabkar@iinternode.on.net> put finger to keyboard and composed:

Anyway I've ordered the diode
and I'll report back once I've tried it.

I replaced the HV diode and all appears well so far.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[William R. Walsh]

Hi!

I remember way back on an old Norelco microwave, the controller
failed, so I got out the old mechanical timer just like the one
on my first Heathkit microwave. I can't stress how this simple
and easy to use feature is missing on todays ovens.

I'm not sure I follow what you are saying. Are you saying that the
microwave, when its controller went bad, failed in an "on" position?
If I understand you correctly, I think it would be a far better idea
to have the oven fail in an "off" position.

I think on better models they used aother timer to cycle
the defrost.

Older microwaves sometimes had multiple timers. My grandfather has a
Litton microwave oven with two timers. One is the main timer, which is
an analog "knob" on the front. The other "timer" is engaged and used
in conjunction with the main timer when DEFROST mode is turned on. It
consists of a slow turning motor that drives an irregular cam. When
the cam rises up, it turns on a microswitch that enables the high
voltage and magnetron.

Today, the controller board in a "typical" oven has two relays...one
that runs the fan, turntable and light and another that can be turned
on and off to cycle the magnetron.

I'm not sure how long that technique was used, as I have a slightly
newer Litton microwave oven that is largely the same internally but
has a "rolling digits" timer and a solid-state control board for the
defrost and low power modes.

Those older models had at least 3 fail safe microswitches on
them, but the switch took the full current.

Newer microwaves also have multiple microswitches. (At least I have
yet to see one that does not, and that's on ovens manufactured as
recently as a year ago.) However, in normal operation, the microswitch
that interrupts the oven's operation when the door opens is actually a
low voltage signal to the controller board.

William

 

[Tim Shoppa]

On Mar 3, 6:11 pm, Jim Yanik <jya...@abuse.gov> wrote:

the savings is in not having to build an expensive,big transformer.
all that copper is expensive,too.
transformers,being far less complicated,are more reliable.
Inverters have a lot more components,particularly electrolytic caps,that
increase the odds of failure.

Microwave oven transformers are really quite undersized by
conventional engineering standards for the amount of power going
through them. Years of experience with the intermittent application
and detailed electrical+mechanical+thermal engineering for some
overtemp shutdowns is why they don't burn out despite being
undersized.

I suspect that with some experience under the belt that the inverters
can be made as reliable.

A lot of early consumer switching supplies weren't that good in their
first iterations either - electrolytics was at least one cause of the
problems.

Tim.

 

[Rick]

Mike WB2MEP wrote:

On Mar 3, 2:28 pm, Franc Zabkar <fzab...@iinternode.on.net> wrote:

My brother's Panasonic model NN-ST756W inverter microwave oven failed
after one year, just out of warranty. I found a short circuited HV
diode, D702, UX-C2B. The associated 8200pF 3kV capacitor appears OK,
as do the inverter transistors.

The inverter PCB (240V version) is similar to the one in these service
manuals:

http://www.eletrodomesticosforum.com/downloads/microondas/Panasonic_N...http://rc5.ru/upload/panasonic_mw_NN-C2000_(MWO).pdf

Here are several exploded views and parts lists:

http://www.prime-electronics.com.au/trade/cgi-bin/display.pl?brand=PA...http://preview.tinyurl.com/bre9kh

http://www.prime-electronics.com.au/trade/PRICEANDAVAIL/frametest.asp...http://preview.tinyurl.com/ahr8s8

I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types. They seem to be overly
complicated for what they do. I understand that they cook more evenly
in low power modes as a consequence of not having to pulse on and off
like conventional microwaves, but I'd rather not pay a reliability
penalty for this feature. BTW, once the microwave is sitting on my
bench top, the extra weight of a traditional mains transformer is of
no consequence.

The Microwave Oven Repair FAQ appears to bear me out:http://www.repairfaq.org/REPAIR/F_micfaq6.html#MICFAQ_019

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.


Franc,

I don't think they're as reliable as conventional transformer/diode/
cap
power supplies. "Inverter" is just a switching power supply that
steps
up the voltage, and consumer-grade SMPS in a variety of products have
a
rather high failure rate.

There were several threads on SER a few years ago when Panasonic
first came out with the Inverter oves, about failures of the Inverter
circuit. At that time, Panasonic wouldn't sell replacement parts for
the Inverter power supply, or even provide a part number for the
switching trasistors that were failing. You had to replace the whole
power supply, which cost almost as much as a new oven.

The service manual for the NN-C2000 you linked to does have a parts
list for the Inverter board, so maybe they are considered repairable
now.

3 or 4 years ago, we needed a new microwave for the break room at
work.
Somebody donated an old (1984) Panasonic with a transformer power
supply,
and shortly thereafter a fancy new stainless-steel Panasonic Inverter
microwave was purchased. The two were used side-by-side for just over
a
year, then one day I came in and saw the Inverter oven set outside for
trash pickup.

So, I would definitely avoid the Inverter microwaves. Other
manufacturers
may be using switching power supplies, just not using the "Inverter"
name.
Last time I checked, most of the microwaves were still using
transformer
power supplies, but once the cost of a switching supply becomes less
than
a conventional supply, I would expect most of them to change over to
SMPS.

When you go into the store, just lift up the right side of each
microwave
on display, and buy the heaviest one.

Mike
WB2MEP

Heh - there's a Buyer's Guide tip you will never see in Consumer
Reports. <g>

My favorite microwave oven is the Sharp "Carousel II" I pulled out of
the trash in 1994. Replaced an open fuse for about 50 cents and it's
been working fine ever since. I used that Sharp to replace a newer,
smaller model with less capacity and never regretted that decision.

It's a shame how many of the older models I've seen tossed that only
needed a fuse replacement.

Rick

 

[Samuel M. Goldwasser]

Rick <rickajho@rcn.com> writes:

Mike WB2MEP wrote:

On Mar 3, 2:28 pm, Franc Zabkar <fzab...@iinternode.on.net> wrote:

My brother's Panasonic model NN-ST756W inverter microwave oven failed
after one year, just out of warranty. I found a short circuited HV
diode, D702, UX-C2B. The associated 8200pF 3kV capacitor appears OK,
as do the inverter transistors.

The inverter PCB (240V version) is similar to the one in these service
manuals:

http://www.eletrodomesticosforum.com/downloads/microondas/Panasonic_N...http://rc5.ru/upload/panasonic_mw_NN-C2000_(MWO).pdf

Here are several exploded views and parts lists:

http://www.prime-electronics.com.au/trade/cgi-bin/display.pl?brand=PA...http://preview.tinyurl.com/bre9kh

http://www.prime-electronics.com.au/trade/PRICEANDAVAIL/frametest.asp...http://preview.tinyurl.com/ahr8s8

I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types. They seem to be overly
complicated for what they do. I understand that they cook more evenly
in low power modes as a consequence of not having to pulse on and off
like conventional microwaves, but I'd rather not pay a reliability
penalty for this feature. BTW, once the microwave is sitting on my
bench top, the extra weight of a traditional mains transformer is of
no consequence.

The Microwave Oven Repair FAQ appears to bear me out:http://www.repairfaq.org/REPAIR/F_micfaq6.html#MICFAQ_019

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
Franc,
I don't think they're as reliable as conventional transformer/diode/
cap
power supplies. "Inverter" is just a switching power supply that
steps
up the voltage, and consumer-grade SMPS in a variety of products have
a
rather high failure rate.
There were several threads on SER a few years ago when Panasonic
first came out with the Inverter oves, about failures of the Inverter
circuit. At that time, Panasonic wouldn't sell replacement parts for
the Inverter power supply, or even provide a part number for the
switching trasistors that were failing. You had to replace the whole
power supply, which cost almost as much as a new oven.
The service manual for the NN-C2000 you linked to does have a parts
list for the Inverter board, so maybe they are considered repairable
now.
3 or 4 years ago, we needed a new microwave for the break room at
work.
Somebody donated an old (1984) Panasonic with a transformer power
supply,
and shortly thereafter a fancy new stainless-steel Panasonic Inverter
microwave was purchased. The two were used side-by-side for just over
a
year, then one day I came in and saw the Inverter oven set outside for
trash pickup.
So, I would definitely avoid the Inverter microwaves. Other
manufacturers
may be using switching power supplies, just not using the "Inverter"
name.
Last time I checked, most of the microwaves were still using
transformer
power supplies, but once the cost of a switching supply becomes less
than
a conventional supply, I would expect most of them to change over to
SMPS.
When you go into the store, just lift up the right side of each
microwave
on display, and buy the heaviest one.
Mike
WB2MEP

Heh - there's a Buyer's Guide tip you will never see in Consumer
Reports. <g

My favorite microwave oven is the Sharp "Carousel II" I pulled out of
the trash in 1994. Replaced an open fuse for about 50 cents and it's
been working fine ever since. I used that Sharp to replace a newer,
smaller model with less capacity and never regretted that decision.

It's a shame how many of the older models I've seen tossed that only
needed a fuse replacement.

Still use our Sharp "Carousel II" from around 1987 and it's never even
needed a new fuse.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[Jim Yanik]

sam@repairfaq.org (Samuel M. Goldwasser) wrote in
news:iqmkqgwl.fsf@repairfaq.org:

Rick <rickajho@rcn.com> writes:

Mike WB2MEP wrote:

On Mar 3, 2:28 pm, Franc Zabkar <fzab...@iinternode.on.net> wrote:

My brother's Panasonic model NN-ST756W inverter microwave oven
failed after one year, just out of warranty. I found a short
circuited HV diode, D702, UX-C2B. The associated 8200pF 3kV
capacitor appears OK, as do the inverter transistors.

The inverter PCB (240V version) is similar to the one in these
service manuals:

http://www.eletrodomesticosforum.com/downloads/microondas/Panasonic_
N...http://rc5.ru/upload/panasonic_mw_NN-C2000_(MWO).pdf

Here are several exploded views and parts lists:

http://www.prime-electronics.com.au/trade/cgi-bin/display.pl?brand=P
A...http://preview.tinyurl.com/bre9kh

http://www.prime-electronics.com.au/trade/PRICEANDAVAIL/frametest.as
p...http://preview.tinyurl.com/ahr8s8

I'm wondering if inverter microwaves are any less reliable than
traditional transformer/capacitor types. They seem to be overly
complicated for what they do. I understand that they cook more
evenly in low power modes as a consequence of not having to pulse
on and off like conventional microwaves, but I'd rather not pay a
reliability penalty for this feature. BTW, once the microwave is
sitting on my bench top, the extra weight of a traditional mains
transformer is of no consequence.

The Microwave Oven Repair FAQ appears to bear me
out:http://www.repairfaq.org/REPAIR/F_micfaq6.html#MICFAQ_019

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
Franc,
I don't think they're as reliable as conventional
transformer/diode/ cap
power supplies. "Inverter" is just a switching power supply that
steps
up the voltage, and consumer-grade SMPS in a variety of products
have a
rather high failure rate.
There were several threads on SER a few years ago when Panasonic
first came out with the Inverter oves, about failures of the
Inverter circuit. At that time, Panasonic wouldn't sell
replacement parts for the Inverter power supply, or even provide a
part number for the switching trasistors that were failing. You
had to replace the whole power supply, which cost almost as much as
a new oven. The service manual for the NN-C2000 you linked to does
have a parts list for the Inverter board, so maybe they are
considered repairable now.
3 or 4 years ago, we needed a new microwave for the break room at
work.
Somebody donated an old (1984) Panasonic with a transformer power
supply,
and shortly thereafter a fancy new stainless-steel Panasonic
Inverter microwave was purchased. The two were used side-by-side
for just over a
year, then one day I came in and saw the Inverter oven set outside
for trash pickup.
So, I would definitely avoid the Inverter microwaves. Other
manufacturers
may be using switching power supplies, just not using the
"Inverter" name.
Last time I checked, most of the microwaves were still using
transformer
power supplies, but once the cost of a switching supply becomes
less than
a conventional supply, I would expect most of them to change over
to SMPS.
When you go into the store, just lift up the right side of each
microwave
on display, and buy the heaviest one.
Mike
WB2MEP

Heh - there's a Buyer's Guide tip you will never see in Consumer
Reports. <g

My favorite microwave oven is the Sharp "Carousel II" I pulled out of
the trash in 1994. Replaced an open fuse for about 50 cents and it's
been working fine ever since. I used that Sharp to replace a newer,
smaller model with less capacity and never regretted that decision.

It's a shame how many of the older models I've seen tossed that only
needed a fuse replacement.

Still use our Sharp "Carousel II" from around 1987 and it's never even
needed a new fuse.

My Carousel from early 1980s blew the HV capacitor after about 20
yrs,replaced it and the HV diode for $25 several years ago,it's still
running.
The MWs of today don't have as tall a cavity as my Sharp's.

--
Jim Yanik
jyanik
at
kua.net

 

[William Sommerwerck]

The MWs of today don't have as tall a cavity as my Sharp's.

But I suspect it's not as wide.