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Posted by Doug Warner on January 2, 2006, 9:47 pm
It worked OK last night, I popped in a meal tonight, pressed the
button.. Overload hum, blue flash from the back, then no display (10
year old Sharp model.)
Since my background is in electronic repair, I opened it up. put a new
fuse in, tried again and saw the flash location, near the big cap in
the rear.. (Unplugged, checked for charge, then metered it. 2 ohms!)
Just to make sure it was really shorted, I connected it in series with
a 1156 automotive bulb and a 12V source. The bulb lights. It's
really shorted.. =20
It's odd that it went from OK to shorted overnight, but the big
question is: Is there typically any collateral damage when this
happens?
(The diode is OK)=20
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Posted by Edwin Pawlowski on January 2, 2006, 10:07 pm
show/hide quoted text
> Since my background is in electronic repair,
So, shouldn't you be telling us what the problem is?
show/hide quoted text
> It's odd that it went from OK to shorted overnight,
I thought shorted was shorted. Did you expect it to be a little shorted at
first? Sort of like being a little pregnant?
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Posted by Don Klipstein on January 2, 2006, 11:53 pm
show/hide quoted text
>It worked OK last night, I popped in a meal tonight, pressed the
>button.. Overload hum, blue flash from the back, then no display (10
>year old Sharp model.)
>Since my background is in electronic repair, I opened it up. put a new
>fuse in, tried again and saw the flash location, near the big cap in
>the rear.. (Unplugged, checked for charge, then metered it. 2 ohms!)
>Just to make sure it was really shorted, I connected it in series with
>a 1156 automotive bulb and a 12V source. The bulb lights. It's
>really shorted..
>It's odd that it went from OK to shorted overnight, but the big
>question is: Is there typically any collateral damage when this
>happens?
>(The diode is OK)
It is normal for capacitors to work just fine and dandy and then totally
short (or open) suddenly with no warning. Early warning, if any, is
changes in leakage resistance or in dissipation factor or slight change in
capacitance - and you have to take the capacitor out, discharge it, and
measure these characteristics. Occaisionally the capacitor may run warmer
when it is in its final months or days.
But expect no warning.
Electrolytic capacitors (which the high voltage one in a microwave is
not) sometimes give warning signs of deteriorating performance or
overheating that may be noticed without removing and testing the
capacitor. My experience is that electrolytics that obviously start going
downhill fail (or become unusable or, in the case of CRT monitors, cause
something else to fail) in a few months.
If the diode is still good, chances are nothing went bad except the
capacitor.
- Don Klipstein (don@misty.com)
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Posted by FDR on January 2, 2006, 11:54 pm
It worked OK last night, I popped in a meal tonight, pressed the
button.. Overload hum, blue flash from the back, then no display (10
year old Sharp model.)
Since my background is in electronic repair, I opened it up. put a new
fuse in, tried again and saw the flash location, near the big cap in
the rear.. (Unplugged, checked for charge, then metered it. 2 ohms!)
Just to make sure it was really shorted, I connected it in series with
a 1156 automotive bulb and a 12V source. The bulb lights. It's
really shorted..
Nitpicking here, not really shorted, but appears to be acing like a resistor
than a capacitor from what you describe.
It's odd that it went from OK to shorted overnight, but the big
question is: Is there typically any collateral damage when this
happens?
I am not familar with the schematics of microwave circuits, but is the cap
failure the cause, or was it a result of another part failing? Are you sure
the diode isn't trashed? How are you testing it? The breakdown voltage
isn't your typical voltage considering the application. If I were tring to
fix your oven I'd replace the diode too.
(The diode is OK)
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Posted by Joseph Meehan on January 3, 2006, 7:39 am
Doug Warner wrote:
show/hide quoted text
> It worked OK last night, I popped in a meal tonight, pressed the
> button.. Overload hum, blue flash from the back, then no display (10
> year old Sharp model.)
It's ten years old. Just replace it. You will like the newer one.
It has been my experience that if I repair something like that it is
likely to need an even more expensive repair next week.
show/hide quoted text
> Since my background is in electronic repair, I opened it up. put a new
> fuse in, tried again and saw the flash location, near the big cap in
> the rear.. (Unplugged, checked for charge, then metered it. 2 ohms!)
> Just to make sure it was really shorted, I connected it in series with
> a 1156 automotive bulb and a 12V source. The bulb lights. It's
> really shorted..
> It's odd that it went from OK to shorted overnight, but the big
> question is: Is there typically any collateral damage when this
> happens?
> (The diode is OK)
--
Joseph Meehan
Dia duit
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