Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

[neilc6]

This TV is model LC-50LB481C. Think C suffix is for Canadian version. U suffix for US so LC-50LB481U.

It is branded Best Buy Recycles (Best Buy repaired and resold??). It is missing 2 ground screws on the PS board, 1 ground screw on the main board and both the tcon shield and screws. I borrowed some screws from the cable clips to ensure it was grounded.

When first plugged in, backlights come on for a few seconds, a quick bright backlight flash and then goes out. No picture.

When power button is pressed, TV attempts to boot, front led slow blinks, millisecond quick backlight flash and front led goes out.

When power button pressed second time, hear a click and front led has fast 2 blink code.

PS connector
ON/OFF 3.9V
+12-A 0V
+12V 12.1V
+5V 0V (problem? or unused)
DIM 3.0V when backlights are on, 3.6V/3.9V when not on
PS_ON 3.4V

main filter caps = 159V

LED strips test good with tester - voltage 62V, 63V
3 red/black pairs going to LED strips, 2 of the pairs are wired in parallel
Backlights off 48.7V, 48.8V
Backlights on 56V, 56V

Anyone have service manual for 2 blink code? Power supply??

[mmartell]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

No Picture meaning you've done the Flashlight Test ?

[dick_barton]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

So you have no +12-A or +5V when you power up the set?

[Andrew F. Ali]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

There are two sets of wires on the connector that goes to the Main Bd. from the PSU. What are the pin Nos. and labels for this connector and what are the voltages you get on each of the pins at plug-in to ac and when the Pwr button is pressed??

[neilc6]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

There is no picture when the backlights are on. TV attempts to turn on but fails, backlight is on for a few seconds before turning off. Measure 12V on both sides of tcon main fuse.

ON/OFF - 3.5V after plug in, drops to 2.9V after power is pressed and settles to 3.9V
+12V - always at 12.1V
+5V - always 0
+12-A - always 0
DIM - 3.4V after plug in, 2.4V when backlight is on, 3.7V after
PSON - 0V after plugin, 3.3V after power pressed

Front LED is on after plugging in. Slow blinks after power is pressed. Backlights come on for a few seconds. A few more seconds and backlight has short bright flash. Slow blink stops after a few more seconds.

You would think +5V would supply main board but I am getting PS_ON signal and standby LED.

[neilc6]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

Ordered a used power supply board. I would assume more voltages would come up with the PSON signal.

[Andrew F. Ali]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

I am thinking you may have an LED Driver or LED Backlight issue.

[budwich]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

while you are waiting for your board, you might try disconnecting the tcon to panel cables (two?) with power off and see what happens there after to see if sets comes up with lights.

[neilc6]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

I did try disconnecting the tcon ribbon cables one at a time and both and still no picture and no power up. The bright blink is a bit suspicious though.

[budwich]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

both disconnected at the same time?

[nomoresonys]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

Little more focused pic. of ps here: seems strange there's no 5v, maybe test powerboard by itself, see if your voltages are there. http://www.shopjimmy.com/sharp-pltvf...c-50lb481u.htm

[neilc6]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

Disconnected both tcon ribbons and exact same behaviour. Unplugged main connector completely and have 12V but no 5V and no +12-A.

It is a Roku TV and missing the remote. I will need a remote in order to set it up if I can fix it since it can be controlled by a Roku app. Looks like it is missing 2 stand screws as well going through the instruction manual (only 1 per side).

[budm]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

+12V and +12VA are fed by the same 12V synchronous rectification supply, if you look at the bottom side of the board you will see that L9101 and L9102 are tied together on on end, so it is probaly measurement error.
The +5V pins are connected to the empty pad that is why there is no 5V. This TV uses 12V STBY.
http://assets.shopjimmy.com/media/ca...au4-bottom.jpg

[neilc6]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

The top silkscreen doesn't match the bottom silkscreen. The bottom one is correct since I measure 12V on 12-A.

http://assets.shopjimmy.com/media/ca...51aau4-top.jpg

Top silkscreen
On/Off DIM
NC PS_ON
+12-A +12-A
GND GND
GND GND
+12V +12V
+12V +12V
+5V +5V

Bottom Silkscreen
On/Off DIM
NC PS_ON
GND GND
GND GND
+12-A +12-A
+12V +12V
+12V +12V
+5V +5V

Main board and tcon are now suspect as well. Disconnected LVDS and still same behaviour.

[nomoresonys]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

Maybe try unplug connector from ps to mainboard and use resistor as jumper to self test the power supply, see if your backlights come on and you get the proper voltages.

[budm]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

The top silkscreen doesn't match the bottom silkscreen. The bottom one is correct since I measure 12V on 12-A.

http://assets.shopjimmy.com/media/ca...51aau4-top.jpg

Top silkscreen
On/Off DIM
NC PS_ON
+12-A +12-A
GND GND
GND GND
+12V +12V
+12V +12V
+5V +5V

Bottom Silkscreen
On/Off DIM
NC PS_ON
GND GND
GND GND
+12-A +12-A
+12V +12V
+12V +12V
+5V +5V

Main board and tcon are now suspect as well. Disconnected LVDS and still same behaviour.

At this point the 12A should be present as you can see how the 12V A is connected to the source, the 5V is not connected to anything so there will be now Voltage there.

[budwich]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

the other problem is that IF the error count for backlights and other errors has been set, you might have to do the "forced power sequence" (ie. channel and vol and cord plug in type thing) other wise, the set may not come on.

[neilc6]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

This model only has one button. Dual function on/off and for input switching. Checking the part number for the main board, 756TXGCC0QK001, it came from a 39" Insignia Roku TV. Shopjimmy indicates two different main boards - 756TXGCC0QK026 and 756TXGCC0QK0040

[nomoresonys]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

At this point the 12A should be present as you can see how the 12V A is connected to the source, the 5V is not connected to anything so there will be now Voltage there.

Right, one of the 12 v is there and one is not, if I read it right.

[Andrew F. Ali]

Re: Sharp LC-50LB481 Two fast blinks Backlight Turns Off No Picture

The StdBy voltage is 12V. DO NOT try to self-test the PSU by using 'a resistor'. You WILL damage your PSU altogether. If you want to self-test your PSU you can take two 1.5V batteries in series connected to the PS-ON and GND.