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Sharp Microwave - no backlight

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  • gurj1979
    Senior Member
    • Dec 2014
    • 129
    • UK

    Sharp Microwave - no backlight

    Need help fixing mums Sharp microwave oven combi.
    R-595 (sl)a
    Backlight has gone. Can still see digits buy super dim.
    Anyone with microwave experience help me out here ?
  • R_J
    R_J
    Badcaps Veteran
    • Jun 2012
    • 9184
    • Canada

    #2
    Re: Sharp Microwave - no backlight

    Are you sure it uses a backlight or is it a VF Display? post pictures of the control board

    Comment

    • stj
      stj
      Great Sage 齊天大聖
      • Dec 2009
      • 29505
      • some shithole run by Israeli agents

      #3
      Re: Sharp Microwave - no backlight

      is that really the part number? or is it R959?

      Comment

      • R_J
        R_J
        Badcaps Veteran
        • Jun 2012
        • 9184
        • Canada

        #4
        Re: Sharp Microwave - no backlight

        If it is a R-959, the display is an LCD with 10 led backlights (D10~D19) in series with a driver transistor Q2
        Last edited by R_J; 08-21-2023, 09:53 PM.

        Comment

        • gurj1979
          Senior Member
          • Dec 2014
          • 129
          • UK

          #5
          Re: Sharp Microwave - no backlight

          Originally posted by stj View Post
          is that really the part number? or is it R959?
          You're correct. it's R959. I must have gotten mixed up with numbers.
          Thanks

          Comment

          • gurj1979
            Senior Member
            • Dec 2014
            • 129
            • UK

            #6
            Re: Sharp Microwave - no backlight

            Originally posted by R_J View Post
            If it is a R-959, the display is an LCD with 10 led backlights (D10~D19) in series with a driver transistor Q2

            Thanks RJ. Sounds right about the number of LED's. There's a good few of them in series. So if I replace that tranny, then all should be good ? Do I need to replace and SMD caps too ?

            Comment

            • stj
              stj
              Great Sage 齊天大聖
              • Dec 2009
              • 29505
              • some shithole run by Israeli agents

              #7
              Re: Sharp Microwave - no backlight

              if the leds are in series a bad one will stop them all
              having said that - it doesnt look like they are driven hard

              Comment

              • gurj1979
                Senior Member
                • Dec 2014
                • 129
                • UK

                #8
                Re: Sharp Microwave - no backlight

                Originally posted by stj View Post
                if the leds are in series a bad one will stop them all
                having said that - it doesnt look like they are driven hard
                It's gradually dimmed over a period of 1 year. So LED's are probably good, but the Driver has failed.
                Any idea what the tranny part number is, or equivalent?

                Comment

                • stj
                  stj
                  Great Sage 齊天大聖
                  • Dec 2009
                  • 29505
                  • some shithole run by Israeli agents

                  #9
                  Re: Sharp Microwave - no backlight

                  no, but try reading the voltage across each led instead of just blindly changing stuff.
                  did you meter the transistor?

                  Comment

                  • gurj1979
                    Senior Member
                    • Dec 2014
                    • 129
                    • UK

                    #10
                    Re: Sharp Microwave - no backlight

                    Originally posted by stj View Post
                    no, but try reading the voltage across each led instead of just blindly changing stuff.
                    did you meter the transistor?
                    I'd have to desolder the whole LCD panel to gain access to the LED's behind it. Thanks Sharp. Lol.

                    Comment

                    • stj
                      stj
                      Great Sage 齊天大聖
                      • Dec 2009
                      • 29505
                      • some shithole run by Israeli agents

                      #11
                      Re: Sharp Microwave - no backlight

                      well if you can get to the transistor you can test that with a meter
                      10 leds in series is gonna need 20-30v so thats what needs to be seen

                      Comment

                      • gurj1979
                        Senior Member
                        • Dec 2014
                        • 129
                        • UK

                        #12
                        Re: Sharp Microwave - no backlight

                        Originally posted by stj View Post
                        well if you can get to the transistor you can test that with a meter
                        10 leds in series is gonna need 20-30v so thats what needs to be seen
                        Ahhh right. I can measure that. I'll try tomorrow. After that I'm on holiday for a week.
                        Will update this post after some results.

                        Thank you guys.

                        Comment

                        • R_J
                          R_J
                          Badcaps Veteran
                          • Jun 2012
                          • 9184
                          • Canada

                          #13
                          Re: Sharp Microwave - no backlight

                          Looks like the supply for the led circuit is around 18 volts, Q1 is the regulator transistor, C4 is the reg. output cap, R4 seems to be 51Ω1W then there is another C10? 47µf/16v so the actual voltage for the leds is likely around 10~12v, the schematic gets blurry when enlarged.
                          Attached Files

                          Comment

                          • gurj1979
                            Senior Member
                            • Dec 2014
                            • 129
                            • UK

                            #14
                            Re: Sharp Microwave - no backlight

                            Originally posted by R_J View Post
                            Looks like the supply for the led circuit is around 18 volts, Q1 is the regulator transistor, C4 is the reg. output cap, R4 seems to be 51Ω1W then there is another C10? 47µf/16v so the actual voltage for the leds is likely around 10~12v, the schematic gets blurry when enlarged.
                            You're a superstar. Thanks for that info.
                            Yes I had that issue with blurriness too.

                            Comment

                            • gurj1979
                              Senior Member
                              • Dec 2014
                              • 129
                              • UK

                              #15
                              Re: Sharp Microwave - no backlight

                              Originally posted by R_J View Post
                              Looks like the supply for the led circuit is around 18 volts, Q1 is the regulator transistor, C4 is the reg. output cap, R4 seems to be 51Ω1W then there is another C10? 47µf/16v so the actual voltage for the leds is likely around 10~12v, the schematic gets blurry when enlarged.

                              What about Q2 ? It's directly connected to the LED.

                              Comment

                              • petehall347
                                Badcaps Veteran
                                • Jan 2015
                                • 3993
                                • United Kingdom

                                #16
                                Re: Sharp Microwave - no backlight

                                Q2 is the driver .

                                Comment

                                • R_J
                                  R_J
                                  Badcaps Veteran
                                  • Jun 2012
                                  • 9184
                                  • Canada

                                  #17
                                  Re: Sharp Microwave - no backlight

                                  Originally posted by gurj1979 View Post
                                  What about Q2 ? It's directly connected to the LED.
                                  Yes Q2 collector connects to the led string, the emitter connects to a 27Ω resistor which connects to the +18 supply. The transistor base gets biased on by D5,D6 and R5

                                  Comment

                                  • gurj1979
                                    Senior Member
                                    • Dec 2014
                                    • 129
                                    • UK

                                    #18
                                    Re: Sharp Microwave - no backlight

                                    Originally posted by R_J View Post
                                    Yes Q2 collector connects to the led string, the emitter connects to a 27Ω resistor which connects to the +18 supply. The transistor base gets biased on by D5,D6 and R5
                                    Thank you

                                    Comment

                                    • stormanimal83
                                      Member
                                      • May 2014
                                      • 48
                                      • Germany

                                      #19
                                      Re: Sharp Microwave - no backlight

                                      ... sorry folks... never mind... but in my oppinion a microwave oven is dangereous to fix and not worth to fix... take care of what u doin and think about what i said... i would never ever open such a thing... not worth riskin´yours and others health...

                                      Comment

                                      • stj
                                        stj
                                        Great Sage 齊天大聖
                                        • Dec 2009
                                        • 29505
                                        • some shithole run by Israeli agents

                                        #20
                                        Re: Sharp Microwave - no backlight

                                        buy the guy a new oven then.

                                        there are lots of things that fail in microwaves that arent related to the high voltage capacitor.
                                        newer machines may not even have one if they are invertor-driven.

                                        Comment

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