Microwave Oven Repair Questions

[George7941]

I replaced a blown fuse in a Samsung microwave and it is working well now.

1) Before putting the cover back on I tested the oven. Are there any radiation dangers associated with running the microwave without the cover on? Electrical dangers are not an issue for me since I work with electricity frequently and take the necessary precautions.

2) I discharged the high voltage capacitor by using the tips of a needle nose plier. Acceptable? There was no arcing during the couple of times I discharged the capacitor.

3) The 20A fuse had 14 amps running through it when the microwave ran, as measure by a AC clamp meter. So it is either a less than 120V current through the fuse or the voltage and current through the fuse were highly out of sync, for an oven running on a 15A 120V supply.

 

[SZR48207]

You ran the microwave with the shielding off? For how long and how close?

 

[George7941]

30 seconds and I was about four feet away. The metal cover on the top of the microwave was off.

Correction. I was about a foot away for about ten seconds while I checked the amp clamp.

 

[PimTac]

You are cooked.

 

[Donald]

Has a second head grown or a sixth finger? If not you may be OK. Had all the kids you are planning on?

Did the buzzer go off and indicate that you are done?

 

[StevieC]

The the local TV repair shop where my dad's friends work also repaired Microwaves and they would always run them with the cover off. As far as I know (but not sure) it's just the cooking chamber that matters.

 

[Dave Sherman]

If you didn't disturb the waveguide then you're probably OK.

 

[Virtus_Probi]

Originally Posted by StevieC
The the local TV repair shop where my dad's friends work also repaired Microwaves and they would always run them with the cover off. As far as I know (but not sure) it's just the cooking chamber that matters.

My understanding is that the cooking chamber is designed to absorb the excess radiation and the cover of the unit would only provide a secondary shielding effect.
Couldn't hurt to screen your groin with some kind of metal if you do this again and also might have children in the future...

There was an elderly professor at my university who was the nicest guy in the world, but had just crazy looking eyes and something very strange with his nose. The rumor around the engineering building was that he worked on early radar during WWII and it was common to look down the waveguides to check for blockages without shutting the magnetron down when the transmitted power seemed to be lower than expected. He was about the right age for that, don't know if it was true at all but it made me very careful about anything generating high energy EM waves...

 

[PandaBear]

It is not ionizing, so by now if you are ok you are ok. Like Dave Sherman and StevieC said the power should be inside the wave guide and the chamber.

You can damage the cap by shorting it even with a needle nose. Next time find a resistor and let it discharge through a resistor instead (the higher resistance the better), use a volt meter to check the voltage and see when to stop. My coworker once dropped a silicon into a power supply, shorting it, and it blew up and sprayed sharp silicon bits everywhere.

20A fuse for a 14A load make sense, you want some safety margin. You don't want customers complaining fuse blowing left and right because it is too close to the limit.

 

[gathermewool]

Originally Posted by PandaBear
It is not ionizing, so by now if you are ok you are ok. Like Dave Sherman and StevieC said the power should be inside the wave guide and the chamber.

You can damage the cap by shorting it even with a needle nose. Next time find a resistor and let it discharge through a resistor instead (the higher resistance the better), use a volt meter to check the voltage and see when to stop. My coworker once dropped a silicon into a power supply, shorting it, and it blew up and sprayed sharp silicon bits everywhere.

20A fuse for a 14A load make sense, you want some safety margin. You don't want customers complaining fuse blowing left and right because it is too close to the limit.


At work we use very large shorting probes to discharge capacitors. I wouldn't trust your typical home-owner to literally short a cap with a small resistor, for fear of blowing the resistor or overheating it, causing personnel injury or equipment damage.

What voltage are these caps operating at?

Are there options for time-delayed fuses? I guess it doesn't matter, because a fault will likely quickly blow a (slightly) too large fuse (e.g., 20A for 14A circuit, such as in your example) without causing erroneous faults.

 

[George7941]

I understand these capacitors operate at 1000V +.

The fuse I installed is a Type ABE ceramic fast acting fuse
http://www.flying1688.com/download_file.php?id=351&f=1

 

[nomas]

Look at the cap and if it says " Protected " on it , you're going to want to use a 20k resistor to short it out . It has an internal fuse link and a dead short might develop enough current to open it . This procedure is for any cap marked that way .