# Microwave help (electronics and Power issue)



## kgt (Mar 31, 2005)

I have a Panasonic microwave NN-S950WA which belongs to my parents. It will start but stops in few seconds (10 to 15 secs.) Clock and functions are working fine. During a lightning strike it hit entire house that killed their microwave, TV, cordless phones, etc. I tried to trouble shoot microwave. The fuse is OK. I believe it is Low Voltage Transformer which is located on a circuit board that is behind touch pad board. Transformer is reading 200-300 ohms which is OK. But there is a varistor to protect circuit in high power surges. I checked this varistor and it seems like bad. I removed it and microwave still does the same. Do you think I have to replace the varistor for microwave to perform if everything else is OK? I learned that it can run without varistor as it's function is to only absorb high voltage spikes during abnormal cases. Please help and let me know if I need to check anything else.


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## O111111O (Aug 27, 2005)

If it's starting/stopping like that, it could be the HV doubler diode/Magnetron.

Unplug, discharge all HV capacitors, check, check HV doubler diode to Magnetron, check impedence across magnetron with it disconnected.


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## johnpost (Dec 18, 2005)

you said that the low voltage transformer might be at fault and then
you gave a resistance value and said it seemed OK. It can't both 
maybe be at fault and maybe OK. Transformers also have more 
than one resistance value.

If the varistor's function is to protect against surges and
you remove it then the circuit should still work. So everything
is not OK except for the varistor being blown.

A varistor is placed where it could divert a surge and maybe
protect other circuitry. If a varistor is taken out that doesn't
mean the other circuitry was protected, the other circuitry
could have been destroyed along with the varistor.

There are things in a digital microwave you couldn't
test without microprocessor test equipment. There
are clocks, counters and memory that could all have
been destroyed. If it can't count past 15 seconds
then it could easily be that.

Be careful even people with years and decades of
electronic experience have died or been severly
injured repairing microwaves. If you aren't really
skilled and know what you can mess with, it might
be better to just replace the whole unit.


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## kiwiguy (Aug 17, 2003)

Also from experience I will confirm that afetr any lightning surge, even repaired appliances seldom last long.

Everything is stressed to the point that MTBF (mean time before failure) rates for all components are all past their use by date. 

As above the varistor (if shorted) would blow the fuse, that is what it is there for. If open circuit, it would have no effect, it simply would no longer be able to offer protection. So it will not be the cause of your problems.

You will find that the microwave will make a satisfying "thud" when you chuck it in the rubbish skip. 

You could well be endangering your own and others lives if you persist in trying to repair it without the knowledge or experience, or the tools and test equipment. As well noted above.


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