Sharp Microwave LCD Backlight problem

[mikeu]

Hi,

A friend has a Sharp Microwave Model R-314FS, manufactured in July 2002. The led backlight is out for the LCD display. All three surface mount leds are good - no power to them. The controller board has a limited number of parts (other than the processor board) for the power supply. We have no schematic and all I have is the board to troubleshoot - He has the rest of the oven.
Does anyone know if there is a common fix for this issue? There are two digital transistors on the board an A123JSC and a D143ESA. I can't really tell if these are bad or not since they test leaky on my transistor tester due to the internal resistors. The other caps and diodes on the board seem ok!
Any ideas?
If the transistors are the culprit - anyone know a source?

Thanks,

Mike

[Bigglez]

The led backlight is out for the LCD display. All three surface mount leds are good - no power to them.

Expect the LEDs to be series connected with a resistor. In a series
circuit any failure will stop the entire chain, even poor or broken
contacts and connectors.

There are two digital transistors on the board an A123JSC and a D143ESA. I can't really tell if these are bad or not since they test leaky on my transistor tester due to the internal resistors. The other caps and diodes on the board seem ok!

Before it broke did the oven turn the backlight on and off
at different times during the cooking cycle? Did the oven
have a standby mode with the internal power on and the
LEDs off?

If so the LED circuit might have a switch driven by the uC.
You should be able to follow the signal from the uC to the
LEDs with a VOM or DMM.

Here's the datasheet for the PNP version
Here's the datasheet for the NPN version

If these are indeed damaged you can deduce that from in circuit
resistance measurements (power off and between the part's pins).
Confirm it again out of the circuit.

[dacflyer]

finding schematics for microwave boards are next to impossible.. if push comes to shove, i'd be willing to look at it, if you wanted to send it to me.. i have worked on microwaves for many years..

[JerryR]

Few years back I was able to get a copy of the service manual for a SHARP microwave oven from Tritronics. http://www.encompassparts.com/tritronics//
Their phone # 1-800-638 3328.
Worth a shot.
HTH
JerryR