Microwave Question

[supersurgilator]

My parents 19 year old Sharp microwave started acting up. My dad went to heat something and said it made a horrible noise and wouldn't heat. They both thought that it did well to last 19 years, I on the other hand was disappointed as I thought it would have lasted longer LOL. Anyway, we went shopping and picked up a new Sharp as that is what they wanted since the other lasted so long.
Anyway, after we got the new one, I flipped the old one over and discovered that both of the air vents on the bottom were completely blocked with a greasy dust looking stuff. I'm a bit scared to try it, but I really wonder what was wrong with the old one. Do you think it might be ok with the vents cleaned, or that the magnetron is toast.

 

[whirlcool]

I had a Litton do that once. It made a very loud humming noise when turned on. It turned out to be a diode in the power supply. I think it cost something like $15.00 to fix back in 1982 or so. After I fixed it the oven was as good as new to this very date.

 

[fido]

If it is going to be thrown away anyway you could dismantle it and look for visible damage. There is a mica window on the inside surface that allows the microwaves into the oven cavity. If that is blackened on the magnetron side it is likely that part of the magnetron has vapourised. The odd noise could possibly be just a problem with the cooling fan so you could check if that is turning freely.
You need to be aware that the capacitor in the high tension circuit for the magnetron can retain a lethal charge of electricity for some minutes after the oven has been used but if it has not been powered up for several hours it will be safe to touch. If it has a metal turntable or any other metal accessories inside you could try it with those removed before you do any dismantling. For testing you just need a mug half full of water.

 

[rolls_rapide]

No! DO NOT DISMANTLE!

The capacitor could well retain a lethal charge irrespective of whether it has been disconnected for several days.

Dismantling and reassembling can't be condoned either: there could be leakage of radio frequency energy from ill-fitting covers or a misaligned door, should the appliance be switched on again.

Do not fiddle with it!

 

[fido]

The capacitors have an internal bleed resistor which slowly discharges them when not in use. I've worked on hundreds of microwaves and never got a hint of a shock off one.

 

[tolivac]

NEVER trust your life to a bleeder resistor!!!they can open unepectedly at any time-thus the cap stays charged.You will have to discharge it yourself if you have the tools and knoweledge.Bleeder resistors are in the transmitters-and they do fail.and in some circuits the bleeders can't be used.In the transmitters I deal with ALL caps are grounded out with a grounding spider or ground hooks.A screwdriver--with a non broken plastic handle will work.Just be sure you don't touch any part of the oven while grounding the cap.Even with bleeders-ground the cap anyway.the life you save may be your own.