Sound and picture but no backlight

[JCdes]

Model tv is RCA LED46C45RQ, mainboard is T.RSC8.78, power supply number is RE46HQ1004, also has RS126S-3T01 on it. I tested the led strips with the led tester and all of the leds light up.

With the tv on stby I get 58v on all led+ connections, with the tv powered on I get 61v. I can't find a service manual so could it be the power supply led driver?

[dick_barton]

Re: Sound and picture but no backlight

Can you post well focused pictures of your power supply. What is the power supply part number?
You have two mosfets and two diodes close to the led connector socket. Have you checked them?

[JCdes]

Re: Sound and picture but no backlight

Here you go...

[dick_barton]

Re: Sound and picture but no backlight

What is the voltage at BL_ON (CON4) and also between the two legs of EC101 (68uF capacitor)when in and then out of standby. What is the voltage printed on that capacitor.

Can you post a photo of the underside of the power supply.

[JCdes]

Re: Sound and picture but no backlight

Stepped out of the house, I'll be back in about 2 hours with the info. I did measure all that but can't remember if bl on was 3.3 or 5 and ec101 was 375 but cant remember in which state I measured. It is rated at 450v.

[JCdes]

Re: Sound and picture but no backlight

I did notice ec101 discharging in about 2 seconds after power off.

[dick_barton]

Re: Sound and picture but no backlight

Also what is the part number written on U200 on the underside of the board.
When you tested the leds what voltage were they operating at.

If you disconnect the leds can you check what Led+ and Led- voltages peaks at when you power on

[JCdes]

Re: Sound and picture but no backlight

I'm on my way back home, I'll check the part number as soon as I get there. Which leads are you referring to? If you mean the led leads they go up to 83v fully lit with the tester give or take from what I remember.

[dick_barton]

Re: Sound and picture but no backlight

With the led lead connector disconnected I'm interested in if the voltage peaks and then drops. You say 61V peak and then drops to 58V. Was that with the leds connected.

[JCdes]

Re: Sound and picture but no backlight

Yes connected and disconnected... Measured both header without leads and leads connected made no diff.

[JCdes]

Re: Sound and picture but no backlight

Trying to read that chip...

[JCdes]

Re: Sound and picture but no backlight

Ok LD7750RGR

[JCdes]

Re: Sound and picture but no backlight

Better look, got the pic from the web... High voltage pwm controller...

[JCdes]

Re: Sound and picture but no backlight

Traced pin1 on the pwm to pc2

[dick_barton]

Re: Sound and picture but no backlight

I was looking to identify any Led Driver IC. The LD7750 is a PWM controller but it appears to be on the COLD side of the power supply which leaves me puzzled.

[JCdes]

Re: Sound and picture but no backlight

Its on the hot side, I traced it to the octocoupler "pc2" which is an EL817

[JCdes]

Re: Sound and picture but no backlight

Sorry I messed up!!! I was looking at u102

[JCdes]

Re: Sound and picture but no backlight

U200 is marked e19359 0B3350CP

[JCdes]

Re: Sound and picture but no backlight

That's the led driver...

[JCdes]

Re: Sound and picture but no backlight

Here's what I found...