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Microwave Backlighting - General Information

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The subject of microwave repair is a big one, and being Mr. Responsible I will say that you better keep your fingers out of a microwave unless you are plenty familiar with electronics.  Having said that I provide the following information about display backlighting for your viewing enjoyment.  You will probably need a set of security bits to get the main cabinet off.  Don't waste your time with a cold chisel trying to break apart a security screw.


The majority of microwaves have an LCD display.  It may happen that the display fades to zero after some time but the microwave functions normally otherwise.  It is then worth your time to investigate the source of backlighting, which the LCD needs in order to be seen from the front.  Backlighting is most often provided by several surface mounted LED's which are hooked in series to a current controller transistor.  Most often, one or more of these tiny LED's will be smoked and unrecognizable.  However, they will be in the obvious position, just behind the LCD panel.


You now understand that this type of repair requires some electronics background, but it isn't too difficult if you take your time.  The  microwave control module/display module usually snaps out or is held in by a couple of plenty obvious phillips screws.  Plastic snaps are the state of the art - could be interpreted either way.  A multimeter will instantly confirm that one or more (usually 3 in a string) LED's will be faulty.  Note the polarity before going any further and write yourself a note.  Desolder all 3 (if it has 3) LED's carefully using some desoldering braid and a low watt soldering iron.


Measure the physical size of the LED's with a digital vernier set to mm. This is the size of LED you will be ordering from a supplier like DigiKey, Mouser, Newark or similar.  You can pick your color, even, just so the size will fit the little pads on the circuit board. Yes, they are tiny and you will need tweezers to get them in and out.  One trick is to "glue" the new part to the board using liquid flux just before you touch the solder to the ends.  Tiny amounts of solder only!


If you are successful, your display will be back in operation.  If you would rather have someone else do it, there are a couple of good display repair people on the internet.  Remember to keep your fingers away from the high voltage section, and discharge the HV capacitor first, because it is deadly.  Do not short the capacitor's terminals with a screwdriver.  Use the recommended insulated probes and a 1 Meg resistor - the procedure is described in microwave repair manuals.  Don't take my word for it.


Obviously there are other reasons for microwaves to fail -  but a dark display is pretty common and fixing it beats getting a new unit if you have the skills.



Edited by Ghost

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