Sharp Microwave - no backlight

[stj]

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

[gurj1979]

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.

[gurj1979]

Re: Sharp Microwave - no backlight

Kool. Sorry I didn't read properly.

[stj]

Re: Sharp Microwave - no backlight

i was replying to stormanimal

[gurj1979]

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

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.

[stj]

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

[stormanimal83]

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.

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...

[stj]

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.

[stormanimal83]

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...

[gurj1979]

Re: Sharp Microwave - no backlight

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

[R_J]

Re: Sharp Microwave - no backlight

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

[petehall347]

Re: Sharp Microwave - no backlight

Q2 is the driver .

[gurj1979]

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.

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

[gurj1979]

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.

You're a superstar. Thanks for that info.
Yes I had that issue with blurriness too.

[R_J]

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.

[gurj1979]

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

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.

[stj]

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

[gurj1979]

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?

I'd have to desolder the whole LCD panel to gain access to the LED's behind it. Thanks Sharp. Lol.

[stj]

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?

[gurj1979]

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

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?