Question about Panasonic NN-C994S Convection/Microwave Oven

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I replaced low voltage transformer on PCB of display board , and when i started for a while all was ok but next day when i started microven once again this transformer got opened and my oven stopped working, on transformer there are 2 terminal marked P1 and P2, can some one explain why this is happening , is it correct to loop P1 AND P2 externally(as i believe this are looped inside transfomer,and due to some reason gets opened) Please guide on possible cause and rectification

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I had looped externally P1 and P2 and now it is working , to assure myself I also checked current in primary of transformer it was measured to be from 300 mA to 600 mA when I started to use microoven. For safety I had now fixed 2 Amp fuse between P1 and P2. Is that all ok. To add I checked all voltages mentioned on PCB viz. 30volt, 5 volt etc which on measuring were found almost ok. Any comments please

Posted on Mar 29, 2007

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There is something on the secondary side which is drawing too much current. I would check all electrolytic capacitors, zener diodes, transistors, and voltage regulators.

Posted on Mar 29, 2007


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LG ldg3016st has no power on main control panel

Did you have any power surges in the house? Any thunder storms?? even if you are not using a microwave, but it is plugged in , you see the clock?? That means it is getting power and running the clock so while you may not be cooking in it, it is actually using power to run the clock functions. So, if there was a power surge, it damages a part on the main board called the Low voltage transformer. It takes the 120 volts from the wall and drops it down to the voltages the board needs to operate, sometimes 5,12 24 or maybe 30 volts. If the primnary winding gets damaged from a surge of some sort. it will no longer light up if that small transformer was damaged. That can happen without even blowing the fuse as the small wires in the transformer were never meant to carry the 15 or 20 amps the fuse is rated at. So the transformer goes bad and the unit is dead but no blown fuse. Have to check the primary winding of the low volt transformer to see if it has continuity. If not, will need new main circuit board. Sorry But $$$$$

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CS Code

Inspect foil side of HV board for burned tracks toward lower side of board. If burned, check HV capacitors (High Voltage Capacitor Test Procedure) and HV transformers (High Voltage Transformer Test) for a short. Otherwise test other components as outlined above.
Solution: Replace defective components as necessary. If applicable, repair foil trace on HV board.
Hope that helps.........

Aug 29, 2008 | Amana RC17 Microwave Oven

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Panasonic NN-C2003S microwave is completely dead. No lights, no action. Have taken cover off and checked fuse, which looks like it is in good condition.

Would need to check power to main board. A lot of times it is the small low voltage transformer on the main board. If the primary winding goes bad it cant get power to the rest of the board to function. So to start, is there power getting to the low voltage transformer on the main board??Have you had any thunder storms or power surges at your home where it is plugged in? If a home loses its Neutral power line it can mess up a lot of electrical devices in the home. do you notice your lights browning at times. If so you may need to get your power company out to do a load test on you system. But the transformer is a very low amp device and will not blow the main fuse if it goes bad. So you could bhave aburnt trace on the back of the main board or a bad transformer. Best guess. Good luck

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Sharp R-9H84B-display black, cleared display shows "Conv Mix, 88:88 Auto". Short time all dark again. Hit clear happen 2 times then, all dark, no power, can't clear won't start, nothing works.

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I would suggest pulling the control board out and looking on the foil side (opposite the component side) for "ring cracks," most likely on the low voltage transformer's connections.

The board may have the screen-printed reference designator "T1" near the low voltage transformer.


Also be sure the fuse is not easy to turn with your fingertips when it is in the holder. If it is, the fuse holder is too loose and must be replaced (not just squeezed with pliers).

You can order a fuse holder, part number WB06X10034 for $6.49 (subject to change) from the Pros here.

If you have any keypad issues, please note that the membrane keypads for this model have long been discontinued.

FixYa does not directly notify us experts of responses, so if you have other questions, please contact me directly.

- William E. Miller, AS-EET
Microwave Oven Control Panel Repair Nationwide
"Recycling by repairing since 1982"

May 28, 2017 | Sharp Microwave Ovens

1 Answer

Microwave went dead as soon as I started heating. Replaced its fuse:58001220

The klystron or the hi voltage transformer are faulty. The klystron is the part that generates the microwaves. The transformer supplies the voltage to operate the klystron.

Dec 31, 2014 | Microwave Ovens

1 Answer

Kenmore microwave mod. 721.80412500 does not heat, timer,lights,fan ok.possible to try a fuse,before calling sears?

If the fuse were blown, You wouldn't even get a display. If you're handy with a multi-meter, and feel somewhat comfortable making electrical tests, the first thing to check is whether the problem is coming from the low voltage (control) side of the oven, or the high voltage side (transformer, magnetron, capacitor and diode).

Unplug the oven and remove the cabinet cover. Before reaching into the chassis, discharge the capacitor by shorting between the two sides with a screwdriver or similar tool. It can store up to about 2000 volts, and can hurt you badly. A brief touch with your shorting tool is all that's necessary.

Disconnect the wire lead that goes from the power transformer (the largest component on your oven's right side (as you face the door), to the capacitor. Insulate it against any metal contact by wrapping electrical tape around the connector.

Set your meter to test for house voltage (the 200VAC range). Plug the machine in and select a cooking cycle. While it's trying to cook, place your meter's leads on the wires coming from the control board to the primary terminals on the transformer. You're looking for a reading that's reasonably close to 120VAC. If you don't get enough voltage, the problem is with the control board. If you do get the required voltage, the problem is in one of the high voltage components.

Write back with your results for further diagnosis.

Dec 24, 2010 | Kenmore Microwave Ovens

1 Answer

The display panel does not light up so you can see what you are doing. everything else works.

Hello there
To replace the light you will first have to remove the outer shell.
To do this
(1). Remove all of the screws on the back of the microwave that hold on the shell
(2) Remove the screws that are on the bottom.

(3) now the shell should slide off towards the back of the microvave.
Note : this may take a little bit of pressure to get it off ok?

(4) Once the cover is off look towards the fromt of the microwave and
you will see the bulb. now just replace the bulb and reinsert the cover and the screws and you are all done ok? If this does not fix the issue then t
his is probably a bad connection or bad low voltage transformer on the control board.

Dec 10, 2010 | Sharp Microwave Ovens

2 Answers

Does not start. The power cord, plug, etc., are O.K.

Hello :

Maybe there's a problem with the power transformer or the power PCB [ Printed circuit board ] . Or it could be just a fuse . You need to check first . If it's the fuse , then that will be easy to solve , you need only to replace it with new one . But if the problem is with the transformer or with the PCB , you need to take your microwave to the service for repairing .

To locate the fuse, remove the outer cabinet of the unit, which is usually held in place with a few screws. Once the outer cabinet is removed, follow the power cord into the unit. It will take you to the fuse holder, where the fuse sits. The fuse holder is located two or three inches into the unit, and may be attached to a power board .

CAUTION: Your microwave oven is capable of giving you a serious electrical shock, even when it is unplugged. I strongly suggest you seek the assistance of an appliance repair technician when conducting any microwave oven repair .

good luck .

please rate !

Mar 29, 2010 | Emerson MW8625W Microwave Oven

1 Answer

Try to start, no respond, no light digital number...No sound. Already check Electric plug is fine.

microwave ovens have a unique problem that shows itself once in a while .. they cant afford to put in a transformer thats big enough to handle two cycles of input power that have the same phase.. there is circuitry in there that tries to make sure that doesnt happen .. it remembers the "turn off" phase and makes sure the next time its turned on it uses the opposite phase.. this is to prevent transformer saturation .. this is kinda technical but anyhow its going to mess up once in a while .. the results will often be a tripped main circuit breaker ... you can check this (if the microwave plugs in) by simply plugging in a lamp to the same outlet .. if it lights then the circuit breaker is ok .. if it doesnt then thats your problem .. find your fuse box and look for a circuit breaker that is in a different postition than the rest .. you have to switch that off then back on again to reset it .. if power is ok and it still doesnt work then you may have a blown fuse inside the microwave ... thats not a place you want to be unless you really know what your are doing .. the voltage and current inside is enough to quickly kill ..

if you or someone else knows how to work with this dangerous stuff .. then they would first make sure its unplugged for at least 5 min .. then look for a bad fuse or fusable resister in the low voltage power supply (usually 12 volts) .. that supplies power to the computer and display .. nothing else will work if the computer is not working .. there is also a thermal fuse inside that will trip if the thing gets toooo hot .. that can happen if air flow is blocked or you try to use the oven with nothing in it ...

Sep 04, 2009 | Sharp Microwave Ovens

1 Answer

Microwave won't work

Check the AC fuse in side the oven. If the fuse is ok chek the low voltage transformer . If the primary winding is open replace the transformer.

May 25, 2009 | Frigidaire FMT148GP Microwave Oven

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