LC-42LB261U No Picture

[jason123]

a newer TV, Sharp LC-42LB261U shows 7 red flashes then blue on the power LED (I think this is normal), No backlight.

1. I tested the backlight with a tester, and both string turn on. Voltages on the VLED+ (1 and 2) is 41.5 V, VLED- (1 and 2) about 0.115 V)
2. Checked the connector from power to Main board. 12V is showing 19.46V (I thought defective, till I looked at the service manual page 21 - Seems 19.5 nominal is ok?)
3. Buttons are responsive. PS_ON, O/F seem to do what they're supposed to (toggle from 0 to 3.3 V)
4. Disconnected LVDS - No effect
5. Disconnected ribbon cables to panel - No effect - Backlight is still not coming on.

If I'm understanding the service manual correctly (Page 21) it's suggesting replacing the panel? Does not seem right to me unless by Panel they mean "Backlight"?

Thoughts anyone?
Thank you

[budm]

Re: LC-42LB261U No Picture

1) You need to report all the Voltages of the connector of the power supply that goes to the main board.
2) What does the Meter of the LED tester show when you test the LED strings?

[jason123]

Re: LC-42LB261U No Picture

Only one voltage on the connector from PS to Main. That has 19.46V
My tester is a home made (multiple power supplies in series with current limiting resistor) and doesn't have a built-in meter. I'll have to test that again.

I opened the panel and sure enough 3 of the 5 strips have one open LED each - replaced those and it's back to life. Thank you

[budm]

Re: LC-42LB261U No Picture

Only one voltage on the connector from PS to Main. That has 19.46V
My tester is a home made (multiple power supplies in series with current limiting resistor) and doesn't have a built-in meter. I'll have to test that again.

I opened the panel and sure enough 3 of the 5 strips have one open LED each - replaced those and it's back to life. Thank you

The LED's are connected in series so if one goes open circuit then the string will not light up.
You can put the Volt meter on the Anode and the Cathode of the LED string to read the total Vf (Forward Voltage) of the string.

[neilc6]

Re: LC-42LB261U No Picture

You should invest in a LED tester. Failed LEDs are the most common failure in TVs nowadays. The latest models can pump out 300mA and can automatically reverse polarity.

https://ebay.us/ZBB7QQ

[jason123]

Re: LC-42LB261U No Picture

Thank you.. I just ordered one. I've had several 24V power supplies with floating output, so I just put them in series.. I get close to 200V and current limit with an external resistor. Not elegant, but it does the job.. half-ass I guess Thanks

[neilc6]

Re: LC-42LB261U No Picture

I looked it up recently because I thought my tester wasn't working and it ended up being one of the probes. Ended up repairing the banana jack but I ordered a new jack for $1 and new sharp probes would have been $3.

My LED tester gets more use on tvs than my multimeter.

[Tjp444]

Re: LC-42LB261U No Picture

Jason, if you're still following this I'm working on the same model. Got it with no backlights but had sound. Opened it up, 5 failed LED's, fixed those, buttoned it back up, TV responds to the buttons and remote but no video. Did you have to do anything to reset the mainboard? I read somewhere, I think the service manual, that after so many attempts to start up with an error (backlight) it will go into a permanent state of no-start, even if it's fixed. Thanks for your thoughts.

[neilc6]

Re: LC-42LB261U No Picture

You need to confirm your backlights are all working before buttoning it all up. Turn on the tv without the panel connected (it should turn on) and repeat after putting the diffuser panel on. Make sure your tcon ribbons are pushed all the way in and in straight and not crooked.