[bobmac]

Panasonic counter top microwave. Model S762WF

For example, key in 2minutes 22seconds at high heat (10), hit the start button,
and it goes for about 4-5 seconds, (including heat), but then it stops. Clears the display, no error message.

When it first happened, I took the cover off, and found a contact on the door switch appeared to have shorted out (black), but I replaced the blade contact, and it worked after that. For a few weeks. Checked again, and it appears to still be intact, not burned out.

er, um, upon closer scrutiny/reading of other posts, my problem is probably similar to this one..

http://forums.partselect.com/microwa...onds-6565.html


How does one diagnose if the mag tube or hc inverter are toast, or does it matter ? Is it cheaper to buy new, or repair old ?

[PS Staff - Sheila]

If the invert is bad they cost a bout $125.00.

Unfortunately I don't have any information on the Panasonic brand.

[AmpDraw]

A bad magnetron isn't going to cause your display to go blank, usually when the mag is bad it will seem to be working fine but the food just never heats. This sounds like an interlock (door) switch problem most likely. You would need to test the door switches with an Ohm meter. the little switches will be labeled on the side if you look closely, may be 2 or 3 terminals on them, may only be using 2 of the terminals, in any event if you look very carefully at the switches you will see them labeled as "Comm" for Common, "NO" for Normally Open, and "NC" for Normally closed.

With one probe of your meter on Common touch the other probe to the Normal Closed, you should get a reading on your meter of about 0 Ohms. Press the switch in and check your meter and you should get no reading.

From Common to Normally Open you will do the exact same and get exactly the opposite reading on your meter.

From NC to NO terminals (if you have both) you will get no reading at all with the switch pushed in or not.

If you don't get readings like that then the switch your testing is bad.

After this if the switches test good with a meter (can't tell by just looking at them) then its possible the low voltage transformer could be heating up and opening on you after short use. This is not to be confused with your High Voltage Transformer that powers the Magnetron. It will look similar but be much smaller. I don;t have a wiring diagram for this so you'd need to poke around on it with your meter to determine which terminals are for your 120 volts going into it, and which terminals are for your low voltage output that comes out of it and powers the control board. Run the microwave and get it to fail on you while doing a voltage check on those output terminals MAKE SURE YOU ARE NOT ON THE HIGH VOLTAGE TRANSFORMER if in doubt have a service tech fix it for you. If you see the power dropping out and the display going blank then this transformer is your likely problem, specially if you still have your 120Volts detected feeding into it.

If you are still getting power out of it and the display is going blank check the connections feeding power to the control board, if they are good then the control board is your problem.

Sometimes that low voltage transformer is mounted directly on and part of the control board. If this is the case you have to replace both as a single item. I'd focus closer on those door switches though before worrying about any of this.

[raviveni]

I also have same problem for Panasonic model NNT664SF.It looks Board and Inverter unit need to replace.Please let me know if any one have that part.

Thanks,
Rav

[AmpDraw]

NN-T664SF is a good model number, partselect doesn't pull anything up on it and Sears recognizes the model number as a Panasonic Microwave but says no parts are available for this model.

I'd suggest searching Google for parts on this if no one at partselect has an old fashioned book they can use for part number look ups.

Make sure you put the dash in your model number while searching.

Here's a link to it on Panasonics web site, you can try and see if they will sell you parts for it directly...

NN-T664SF - Countertop Microwaves - Shop and Compare at Panasonic

[MikeLeonard]

I found parts for your NN-T664SF
And here's my story...

My Panasonic microwave [NN-S262BF, with inverter] recently failed. It would only run for 2 seconds, making a clicking sound, then shut off. Being a do-it-yourselfer, I searched online for my symptoms and suspected the magnetron. I bought a new one for only $40 at partstore.com, and replaced it.

After reassembly, it did indeed run for 2 minutes and boil 8 ounces of water -- success! Or so I thought... after I reinstalled it over the stove, it failed again with the same exact symptoms. Argh...

So, back to the internet and I even called a local repair shop. They convinced me the problem was the inverter, so I bought a new one for $162 at partstore.com. I just completed that surgery this evening, and now it runs for precisely 23 seconds and shuts off -- never clicking, never heating. Now I'm cursing and losing DIY points with the wife

So, my latest theory is that the bad inverter fried my magnetrons, but it'll cost me another $40 for a new one to find out. Does any one out there actually know anything about this stuff and can give me any advice? The unit is 5 year and 4 months old (just outside the 5-year magnetron warranty), and I had to replace the PC board a few years ago when it failed.

Thanks in advance!