Author Topic: Old Sharp microwave  (Read 1853 times)

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Offline Norm

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Old Sharp microwave
« on: November 04, 2012, 08:42:16 AM »
Anyone have a Sharp microwave and the display fades away?
I have one that still works after 15? years .....3 or 4 yrs. ago
the display faded away learned how to get by without it mostly
reheat coffee....punch clear, hit beverage, count about 15 seconds
for 3/4 cup of cold coffee.
Baked potato....pretty much automatic.....press clear (beep), and
press baked potato.  Oatmeal  put in and watch till it rises and
almost runs over.

Pretty Basic!

Then along comes this power outage for 3 or 4 days....and when it
finally comes on  ....the Sharp display comes on bright and clear just
like when it was new  and displays....Sharp     still  the greatest
and gives me instructions on how to set the clock.....

nice ....works for a couple of days  but then I forget to press clear when I'm
thru using it a couple of times and I noticed it was fading again.....
tried unplugging it for a few hours.....but that didn't work......it's gone again

I can shine a flashlight on the display window at an angle and make out what
it's trying to display ......

any suggestions  or ideas how to bring the display back?   

if I get it back I could unplug it when not in use....but I'd probably get the
 nagging about resetting the clock.....
Norm :)


Offline Wolvenar

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Re: Old Sharp microwave
« Reply #1 on: November 04, 2012, 09:22:28 PM »
LCD? or other kind of display?

Tell you right now its not a repair for someone that doesn't like diving into electronics any which way.

Take a pic of the front I just *might* have a source for a working control / lcd
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Offline Norm

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Re: Old Sharp microwave
« Reply #2 on: November 04, 2012, 09:52:07 PM »
Wolv....
  You mean the whole front of the Sharp?
ila_rendered
[ Specified attachment is not available ]

its like bright LEDs when it was working yet even without them lit I can shine a
flashlight at an angle and see partly the numbers that it should be displaying
but even that not as good as it used to do.....
don't know if the pic will do any good ...but....
Norm

Offline Norm

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Re: Old Sharp microwave
« Reply #3 on: November 04, 2012, 09:55:00 PM »
that's the best I can do with this camera could do better with the other camera but needs a battery
Norm

Offline ghurd

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Re: Old Sharp microwave
« Reply #4 on: November 04, 2012, 10:43:08 PM »
LCD is black numbers, like a new calculator.
They can show up sometimes with light at an angle.

Like Wolv said, not something for normal humans to tinker with.

At the most, I'd take it appart, remove and reconnect the
connectors to the back of the display and the other cable ends too.
If that doesn't fix it... I'd give up right then.

Your microwave situation is better than mine right now.
Push "power time 1 2 5 start" (thats 1 minute 25 seconds for a big mug).
About 75% of the time the display goes to '88:88',
and nothing happens.
Push 'stop / reset',
Push "power time 1 2 5 start",
repeat repeat repeat

I should not complain.  It worked perfect until about 3 months ago.
I think it is 24 years old.  Panasonic.
G-

Offline Wolvenar

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Re: Old Sharp microwave
« Reply #5 on: November 05, 2012, 03:50:40 AM »
I'll take a look, f I can scroung a working one of that model up.
If possible a better image would be nice.

Careful with the connectors, if you do try.

If its not very visibly a connector, don't try pulling it, or you may lose whats left of the display, particularly of its an LCD.
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Offline bj

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Re: Old Sharp microwave
« Reply #6 on: November 05, 2012, 07:50:17 AM »
  Hard to tell for sure Norm, but case trim, keypad etc look the same as a Kenmore we have.
  And Kenmore's could be built by anyone.  Anyway, ours has a florescent display.  (Bright blue)
  And yes, it's not as bright as it used to be either, but still usable.  And it is always better after a rest.
  Maybe useless info, in which case, totally disregard.
"Even a blind squirrel will find an acorn once in a while"
bj

Offline MadScientist267

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Re: Old Sharp microwave
« Reply #7 on: November 05, 2012, 12:41:37 PM »
There is actually a flavor of LCD that is made to look exactly like LED.

The polarizers are flipped so as to provide a black background with "lit up" numbers. Rather than a reflector at the back of the display, there is a backlight in the color the manufacturer desired.

If the numbers were colored, I suspect this is exactly the design, as holding a flashlight up to a dim LED or fluorescent display would make it HARDER to read, not easier. If its an average everyday LCD, the flashlight thing applies as well.

LCD is biased to control contrast, and likely what has happened is the bias supply has drifted, and is probably temperature sensitive now for whatever reason. This would explain it showing up after an extended power failure, but then fading out again a short time later. Trying to reproduce the results didn't work because it probably was not unplugged long enough for whatever is in there that is causing it to cool down sufficiently for the contrast to return to original spec. LCD is very sensitive to this bias; a relatively weak HV static field within several inches of a removed LCD element is enough to change the polarity of the crystals, causing darkening/lightening of the display. As little as 0.3V across any cell in the display can make it completely flip states.

Steve
Wanted: Schrödinger's cat, dead and alive.

Offline bj

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Re: Old Sharp microwave
« Reply #8 on: November 05, 2012, 09:23:49 PM »
  Learned something new again.  That's why I love this place.
  thanks Steve.
"Even a blind squirrel will find an acorn once in a while"
bj

Offline Norm

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Re: Old Sharp microwave
« Reply #9 on: November 05, 2012, 11:16:46 PM »
Yeah Me too....thanks Steve.....
and as long as it works, better than my daughters where the
display works....but the microwave doesn't !
Eh?
Norm.

Offline Norm

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Re: Old Sharp microwave
« Reply #10 on: November 05, 2012, 11:19:40 PM »
BTW bj ours is/was bright green instead  of blue....
which probably means nothing....hmm?
Norm :)

Offline Wolvenar

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Re: Old Sharp microwave
« Reply #11 on: November 06, 2012, 02:40:34 AM »
Believe it or not, her microwave is likely SIGNIFICANTLY easier to fix.

In the microwave circuit ( non inverter style) There are very few components..
Leaving out the control circuits, ( switches, timers, relays etc..)
The components are basically:
A step up coil, a capacitor, a rectifying diode, and a magnetron.

There is a chance of residual high voltages, but most microwave capacitors today have been built with internal resistors/resistance to bleed power off to make the device safer for dum dums like me that love tearing things apart.

I have fixed a LOT of microwaves over the years.
Ironically I started this by scrapping a lot to get the ceramic magnets in the magnetrons for a wind gen.

click on thumbnail for larger image


I have never yet seen a bad coil. A rough guesstimate, and this is counting only totally non-working unit.
I'm not counting display troubled ones (which are a LOT).
About 60% of he microwaves I have messed with are nothing more than a blown fuse, or heat fuse and/or thermostat.
The rest, in order of most common failures:  rectifier, capacitor, magnetron, timer.
There was only one where it was any of the switches or relays ( only 1 of near 200 or so).

If anyone is interested, I suppose I can get into the theory of operation, and how the circuit works.
A microwave is amazingly simple, if you don't count digital controls and timers.


 
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Offline Wolvenar

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Re: Old Sharp microwave
« Reply #12 on: November 06, 2012, 02:51:43 AM »
Norm yours sounds like a LED lit unit. And from the sounds of it you have a failed capacitor.

Capacitors, particularity of that machines era, fail and leak well before they should.
This is generally because these were made in china with an incomplete stolen electrolyte recipe.
More on that here http://en.wikipedia.org/wiki/Capacitor_plague
The result is the electrolyte breaks down earlier than it should and becomes acidic, pretty much ruining the capacitors value.
Sometimes leaking caps leak enough to get on things around it and cause corrosive damage or shorting.

I collect/repair game consoles, and one of the most common problems of these from the 90s is failed capacitors.
I'll add a pic here for an example if I can dig one up.

--Edit --

Here is a couple from a LCD tv I repaired
Don't mistake what you see on these for glue, it DOES look a little like it.

Click image for (much) larger view
Trying to make power from alternative energy any which way I can.
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Offline bj

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Re: Old Sharp microwave
« Reply #13 on: November 06, 2012, 05:41:24 AM »
   Good read Wolv.  Once again, Thanks.
"Even a blind squirrel will find an acorn once in a while"
bj