Sharp LC-42SB45U No Picture, Sound or Response to Button Presses

[Syryll]

Yet another dead TV I picked up to play with. As soon as I apply power to the set, I get a green light with a single flash, and then solid. I can't power the set off or anything.

As far as the connector from PS to the mainboard, these are the readings I get:

CN902
5v: 5.11v
PS_ON: 1.77v
12v: 12.11v
24v: 24.21v
BL_ON: 0.06v

As per other posts, I've tested F1, F2 and F3 on the inverter board. All tested fine.

[budm]

Re: Sharp LC-42SB45U No Picture, Sound or Response to Button Presses

You all the correct Voltages except you do not have BL-0N signal from the main board to turn on the backlights circuit. So you have main baord problem.

[Syryll]

Re: Sharp LC-42SB45U No Picture, Sound or Response to Button Presses

That's what I figured. Thanks!

[Syryll]

Re: Sharp LC-42SB45U No Picture, Sound or Response to Button Presses

I decided to check the panel for cracks and backlight prior to ordering a mainboard. I've got 5v jumped to PS_ON and BL_ON with separate 1k resistors, and I just get backlight for about a quarter of a second when I plug the set in. Do I have to have something on the brightness pin as well, or is something else afoot?

[budm]

Re: Sharp LC-42SB45U No Picture, Sound or Response to Button Presses

When you do the force on using resistors, you MUST remove the cable going back to the main board first, we do not want to back feed the force signal back to the main board.
There should be another pin for dimming control that may need to have the resistor connected as well.

[Syryll]

Re: Sharp LC-42SB45U No Picture, Sound or Response to Button Presses

Yup, it's disconnected from the mainboard. It does have a brightness control pin. It's pin 2 on CN902. How would I go about adding that pin to the jumper? Just add another 1k or so resistor from 5v to that pin?

[budm]

Re: Sharp LC-42SB45U No Picture, Sound or Response to Button Presses

Yup, it's disconnected from the mainboard. It does have a brightness control pin. It's pin 2 on CN902. How would I go about adding that pin to the jumper? Just add another 1k or so resistor from 5v to that pin?

Yes.

[Syryll]

Re: Sharp LC-42SB45U No Picture, Sound or Response to Button Presses

Same results. 1/4 of a second flash then off the backlight goes. I checked 5v, 12v, and 24v to make sure they weren't falling out. They're all steady at their respective voltages.