Sharp Microwave - no backlight

[gurj1979]

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]

Re: Sharp Microwave - no backlight

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

[stj]

Re: Sharp Microwave - no backlight

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

[R_J]

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

[gurj1979]

Re: Sharp Microwave - no backlight

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

[gurj1979]

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

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 ?

[stj]

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

[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?

[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

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

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

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.

[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

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.

[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.

[petehall347]

Re: Sharp Microwave - no backlight

Q2 is the driver .

[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

[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

[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...

[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.