Sharp Microwave - no backlight

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  • stj
    replied
    Re: Sharp Microwave - no backlight

    replacing all 10 was a wise move,
    i found that if you replace an led in anything the brightness/colour usually doesnt match the old ones

    Leave a comment:


  • gurj1979
    replied
    Re: Sharp Microwave - no backlight

    So I found out what the problem was. 1 LED was blown, creating high resistance. Took a long time to desolder the LCD Screen. Got there in the end.
    I ended up replacing ALL 10 Green LED's with Bright White LED's. LOL.
    Works sweet.
    Thanks for all who chipped in to help.

    Leave a comment:


  • gurj1979
    replied
    Re: Sharp Microwave - no backlight

    Kool. Sorry I didn't read properly.

    Leave a comment:


  • stj
    replied
    Re: Sharp Microwave - no backlight

    i was replying to stormanimal

    Leave a comment:


  • gurj1979
    replied
    Re: Sharp Microwave - no backlight

    Originally posted by stj
    the radiation is in the oven cavity, the only times you need to worry is if you mess with the magnetron or the door seal.

    the back of microwaves is not sealed/screened
    Im aware of the dangers, but I wont be touching the megnetron. I only need the keypad/lcd pcb. I've opened it before, 2 years ago, but I didnt have time to fully examine it.

    Leave a comment:


  • stj
    replied
    Re: Sharp Microwave - no backlight

    the radiation is in the oven cavity, the only times you need to worry is if you mess with the magnetron or the door seal.

    the back of microwaves is not sealed/screened

    Leave a comment:


  • stormanimal83
    replied
    Re: Sharp Microwave - no backlight

    Originally posted by stj
    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.
    I don't mean the voltage.... i mean the housing... u'll never now if this thing is closed as it was before.... there is radiation inside... thats what i meant to say... take car...

    Leave a comment:


  • stj
    replied
    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.

    Leave a comment:


  • stormanimal83
    replied
    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...

    Leave a comment:


  • gurj1979
    replied
    Re: Sharp Microwave - no backlight

    Originally posted by R_J
    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

    Leave a comment:


  • R_J
    replied
    Re: Sharp Microwave - no backlight

    Originally posted by gurj1979
    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

    Leave a comment:


  • petehall347
    replied
    Re: Sharp Microwave - no backlight

    Q2 is the driver .

    Leave a comment:


  • gurj1979
    replied
    Re: Sharp Microwave - no backlight

    Originally posted by R_J
    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.

    Leave a comment:


  • gurj1979
    replied
    Re: Sharp Microwave - no backlight

    Originally posted by R_J
    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.

    Leave a comment:


  • R_J
    replied
    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

    Leave a comment:


  • gurj1979
    replied
    Re: Sharp Microwave - no backlight

    Originally posted by stj
    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.

    Leave a comment:


  • stj
    replied
    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

    Leave a comment:


  • gurj1979
    replied
    Re: Sharp Microwave - no backlight

    Originally posted by stj
    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.

    Leave a comment:


  • stj
    replied
    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?

    Leave a comment:


  • gurj1979
    replied
    Re: Sharp Microwave - no backlight

    Originally posted by stj
    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?

    Leave a comment:

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