Power cuts off when starting oven or micro

Yes the light comes on when the door is opened and when the microwave is active! The PF code indicates a Power Failure, press clear or cancel to reset or unplug for a few minutes and re plug!

Microwaves are not very user friendly when it comes to servicing the. They generate very high voltages and are very dangerous to try to repair without the proper training.

PF is Power Failure. Check and see if the Oven has a reset switch or power button. Try and hook up an extension cord, plug one end into a usable output (wall plate) and the other into the 110VA line plug attached to the Oven. Turn on....if it works then the problem is a circuit breaker or wall interface. If it fails with the extension, then it is an electrical problem with the microwave device itself. If there are no Reset features on the oven, an internal fuse may blow, or other shorts are occurring. The cost to fix is more than a new unit. Lowes has them as low as $150.00.

PF means power failure. Quite possibly you a
had a power surge and the control board was damaged.

Make sure that the program controller is working if not check power - step down supply, the pads are responding- if not faulty pads- or the door switches, if the switch contact are not good then it will not trigger the processor to switch on the waveguides. If the lights or fan work without any display or action of program being triggered to start then it can be a possible fault on the main board or the processor. Sometimes insect secretion can short the board and display panel and so the processor can work in such an erratic manner. If so clean, solder and reset the board. Now identify the parts by clicking this link: http://www.espares.co.uk/advice/microwave/a/5/141/identifying-microwave-parts.html

If there is no heating please do not switch on unless you have confirmed the fault. It is possible that the Magnetron is faulty, the temperature cut off is faulty or the main capacitor is short. It is also quite possible that insect can get into the oven and create soft spots. When you switch on these will create a short and make the voltage jump and in the long run damage the magnetron. Check this link to know how a microwave works:

http://www.espares.co.uk/advice/microwave/a/5/1443/how-a-microwave-oven-works.html

Power being interuppted could be anything from a bad fuse , bad fuse holder, bad solder connections on the main board. Bad breaker in your panel. Start by plugging it into an outlet you know is on a different breaker than the on it is on now. See if it does the same thing. If it works ok, then problem with power to the other outlet. If it does the same thing problem inside of unit. PF is Power Failure, now we have to figure out why.

PF = Power failure. Try and push the clear or cancel button (or start, or clock etc) You may have missed one. If that doesn't work try and unplug it for 10 seconds or so and retry.

PF - Power Failure - PF error code indicates a power failure during the cycle.
Press and HOLD start to continue the cycle, or press off/pause to clear display.

Thanks for using FixYa - a 4 THUMBS rating is appreciated for answering your FREE question

Possibly a keypad short or motherboard fault if it is a KitchenAid microwave. Beware if you have a KHMS155LSS model, a Keypad short can and will cause the microwave oven to start on its own. A real stunning defect.

You are decribing a typical Door Safety Switch problem. The Door Safety Switches has Failed.The Door Safety Switch is designed to shut down the Micro in the event the Micro is still cooking when the door is being opened. The first "Click" of the switch cuts off the "Cook". If it does not cut off the "Cook", the second "Click" blows the power. Otherwise it would "Cook" with the door open, and I need not to tell you how DANGEROUS that could be. It first Tripped the Circuit Breaker which supplies power to the Microwave. After Re-Setting the Breaker the same thing happened except this time the Micro is DEAD- not even a light working. Yes, there is a line FUSE inside the Micro. You however need to address the Door Switch SHORT before replacing the fuse. If not, it will just Blow The Fuse Again, and Again, until the Short is corrected.
Call around, ask How much to replace a Door Safety Switch.
Good Luck!