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Friday, 17 February 2017

The Sainsbury's supermarket Microwave Oven....

The wife called me at work...

"Mum's microwave has died, can you have a look?"

Yeah .... why not ...

It's a cheap and cheerful microwave oven from Sainsbury's....

... everything works, except it doesn't get hot.

First things first ... look at the warning in the top right hand corner of my website, the bit in red.

Every microwave ever made, carries this warning... I must insist you follow it's warning.. leave it to the professionals... m'kay?











Right, being the professional, I unscrew the cover to reveal the inner workings of the oven...











Here's an annotated picture...












First thing to check is for safety. The high voltage capacitor can store ~2,500 volts , let's make sure it's safe before going anywhere near it. There's enough charge in there to floor you, or kill you. I check it's dead with a high voltage probe.... It's not charged up ... good.

It's then time to check the high voltage fuse, which turns out to be open circuit :)

Now it's not an ordinary 1.25" fuse. It's a special high voltage fuse. A like-for-like replacement is ordered and fitted.

This poor fuse suffers a lot of stress in it's life, and most seem to fail through old age, rather than protecting a failed circuit.




Here's a diagram of the all important high voltage section I've pinched from a Daewoo manual. It neatly shows the simplicity of the circuit.
















... and here's the obligatory video....

3 comments:

  1. Nice blog, very informative, according to you, what are the top microwave ovens.?

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  2. Thanks. Strange problem with a friends microwave. The main 10A supply fuse was blown. Replacing the fuse and the microwave control section goes on but fails when microwave section is turned on. Removed both wires to the magnetron supply and the diode definitely OK. The capacitor measures the correct capacity but as soon as I screw the diode fast to ground and leave the HT wires connected then it blows again. The multimeter measure no shorts on the transformer capacitor to ground. There is about 100 ohm on the HT terminal to ground as the other end is grounded so I presume this is also OK. Is it possible the capacitor is failing short circuit or to ground through its case at a high voltage. Perplexing ! Any ideas appreciated.

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