Microwave went faulty a few days ago, with the following symptoms, play close attention to the symptoms, as this was leading me to think it was a cap going out, and nothing that serious as the oven was still heating. There are quite a few articles out there on the web where people have replaced transformers, megatron’s, controller boards etc (each costing anywhere from $25 – $100 each), when all they needed to replace was 10 cent cap.

• Garbled buzzing/beeping sound when the door opened, or any cooking function was selected
• The buzzing/beeping sound changes when any of the buttons are pressed, it seemed unwanted electrical signals were getting to the piezo speaker/buzzer
• The oven light flickered in time with the buzzing sound
• Turntable not turning – I recently replaced the turntable motor so I knew it was ok
• It would still heat food even though it was doing all of the above

So, disconnect power, then take the oven off the wall, remove the outer case, then remove the circuit board that hosts the display and control panel.

A guy on appliancepartspros.com forum said cap C1 50v 220uF goes out, so I take a look at that one and the others nearby, they all look ok.  I decided to remove C1 and the other 3 that make up a block of 4, C2 50v 47uF, C3 16v 470uF and C4 2200uF 16v. I tested C1 with my multimeter and sure enough it’s dud, just for good measure I also replaced the others in that block of 4, even though they tested ok.

I then decided to test the other caps next to this block, this column of caps are all the same physical size, unlike the first block of 4 which have various sizes – they are C5 100uF 10v, C6 22uF 16v, C14 22uF 16v, C15 4.7uF 50v. Glad I did, as found that C5 was also dud.

Resistor R51 39k ohm also looked as if it had got hot, which is possible as it works along with the relay which has been chattering away, so I replaced that as well, it did test ok though.

So, to summarized, replace 2 faulty caps and a resistor

C1 50v 220uF

C5 100uF 10v replaced with 100uF 16v, remember it’s usually ok to replace with a higher voltage cap, never lower though.

R51 39k 1% resistor

I leave up to you to decide if you want to replace the other caps that test ok.