LG microwave repair

[John Wayne]

Let me start out by saying I am not an electronics tech but do understand
basic electronics and schematics and have read the s.e.r. microwave faq and
understand the precautions about working on high voltage equipment and
discharging same.
Anyway my problem is my LG over the range microhood.
Got is from a liquidator about a year ago so is not under warranty and from
the near thestart there was the occasional arcing sound which recently got
quite frequent and now it does not heat at all.(or arc).
I pulled the covers and made sure the capacitor was discharged and took a
few measurments and the leads to the magnetron read about 0.8 ohms which
seems ok according to the faq but the diode from the capacitor to ground
reads open both directions so I suspect that is the culprit.
The problem is the intermittent arcing from the start which if I replace the
diode will most likely return and in fact the wave tunnel where the
magnatron is attache to has the paint scorched off of it for about 2" area
above where the magnetron attaches below.
I believe it said something in the faq about touching up the paint for
arcing problems but did not say what kind of paint to use.

So my questions are should I get a replacement diode and remove the
magnetron and clean up the wave tunnel and repaint it and if so with what
kind of paint or does this indicate a problem with the magnetron as well?

If not is it worth putting it back together and taking it in for repair? A
new one like this will run about $275 buck here.

 

[David Farber]

Let me start out by saying I am not an electronics tech but do understand
basic electronics and schematics and have read the s.e.r. microwave faq and
understand the precautions about working on high voltage equipment and
discharging same.
Anyway my problem is my LG over the range microhood.
Got is from a liquidator about a year ago so is not under warranty and from
the near thestart there was the occasional arcing sound which recently got
quite frequent and now it does not heat at all.(or arc).
I pulled the covers and made sure the capacitor was discharged and took a
few measurments and the leads to the magnetron read about 0.8 ohms which
seems ok according to the faq but the diode from the capacitor to ground
reads open both directions so I suspect that is the culprit.
The problem is the intermittent arcing from the start which if I replace the
diode will most likely return and in fact the wave tunnel where the
magnatron is attache to has the paint scorched off of it for about 2" area
above where the magnetron attaches below.
I believe it said something in the faq about touching up the paint for
arcing problems but did not say what kind of paint to use.

So my questions are should I get a replacement diode and remove the
magnetron and clean up the wave tunnel and repaint it and if so with what
kind of paint or does this indicate a problem with the magnetron as well?

If not is it worth putting it back together and taking it in for repair? A
new one like this will run about $275 buck here.

From my experience working with microwave ovens, the diode you speak of
needs a much larger forwarding bias voltage before it conducts. Therefore, a
regular multimeter will show it as open. Take a look at this thread from a
few years back:

http://tinyurl.com/2l772e

 

[William Sommerwerck]

Arcing would presumably be caused by exposed sharp edges in the waveguide or
oven cavity.

I'm not sure what the "correct" paint would be, but it would definitely be
something non-conductive. I would start by cleaning up and repainting the
scorched area.

If you disconnect the oven light, you should be able to see where the arcing
is occurring. Remember that excess exposure to microwaves will coagulate the
proteins in your eye, leading to cataracts or blindness. Be careful.

 

[Sam Goldwasser]

Arcing would presumably be caused by exposed sharp edges in the waveguide or
oven cavity.

I'm not sure what the "correct" paint would be, but it would definitely be
something non-conductive. I would start by cleaning up and repainting the
scorched area.

If you disconnect the oven light, you should be able to see where the arcing
is occurring. Remember that excess exposure to microwaves will coagulate the
proteins in your eye, leading to cataracts or blindness. Be careful.

Paint is for cosmetic purposes and to prevent rust. It won't affect the
arcing. Most non-toxic enamels will be fine, but test in an inconspicuous
area first and let it dry overnight at least.

He will need to check the diode with a voltage greater than 6 V to see if
it conducts in one direction only.

0.8 ohms - if accurate - seems way too high for the magnetron filament.
It should read essentially 0 ohms on a common DMM.

It's possible that the arcing has been due to contamination inside the
waveguide all along, and not anything faulty.

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[whit3rd]

...the diode from the capacitor to ground
reads open both directions so I suspect that is the culprit.
The problem is the intermittent arcing

The 'diode' is a highvoltage stack, so it might normally read open
(depends on your meter); it's possible to test it with a couple of
9V batteries in series with a 10k ohm limit resistor, looking at the
voltage drop
on the diode when excited with 18V.

If there was arcing, you might suspect the interlock switches, and
look for signs of loose connections. The most likely cause of
'complete failure'
is still the fuse. Diode failures are usually not accompanied by
any
noises. Interlock switches with a speck of dust in the contacts
ARE noisy.