Sharp LC-47SB57UT will not power on

[johnboy1313]

I just picked this unit up. It will not power up at all. The fuses are not blown on the power supply.



At the connector above, from top to bottom,
0V
0V
0V
0V
0V
GND
GND
GND
GND
GND
N/A
3.3V
3.3V



At the connector above, from top to bottom,
3.3V
3.3V
0.79V
0.79V
GND
GND
GND
0V
0V
1.4V
4.97V
4.97V




The two pics above are of the same connector with wires and without, it is the other end of the previous connector. From top to bottom
4.97V
4.97V
1.4V
0V
0V
GND
GND
GND
0.79V
0.79V
3.3V
3.3V



The connector above from left to right
GND
1.49V
1.49V
0.15V
1.49V
N/A
GND
1.49V
1.49V
N/A

[tom66]

Re: Sharp LC-47SB57UT will not power on

This is not a Sharp TV. This is a UniHan TV, with the Sharp logo stuck on it. Sharp are selling their name... and it doesn't even use a Sharp panel.

The problem is most likely the main board, this seems to be the most common issue with this chassis (which is more and more prominent.) If you have standby power but no main power, that's where I'd look. And I'd think it's firmware/eeprom, so pretty hard to fix.

[johnboy1313]

Re: Sharp LC-47SB57UT will not power on

Do you know how I could get the power supply to come on all the way to see what happens?

[selldoor]

Re: Sharp LC-47SB57UT will not power on

You might get more members helping you if you posted your pictures using
manage attachments.

[tom66]

Re: Sharp LC-47SB57UT will not power on

The PS pin looks to be the one you need to look at.
Try forcing that to 5V using 5VSB with a 1k resistor.

[randtek]

Re: Sharp LC-47SB57UT will not power on

To force the power supply on, you will need a couple of resistors. I usually use 100 Ohm resistors for this, but it is not critical, anything between about 47 Ohms and 1K Ohms is probably fine. Unplug the TV from the wall. Disconnect the cable that goes from CN903 on the power board by unplugging it from the main board. On this cable you have just disconnected, run one resistor from 5V (yellow wires) to On/Off (Blue wire), and another from 5V to PS On (white wire). Make sure this cable/resistors cannot accidentally short against anything, Plug the TV in to the wall power outlet. You should be able to read all of the power supply voltages with the unit connected in this manner. You will probably see the backlights lit too.

[johnboy1313]

Re: Sharp LC-47SB57UT will not power on

You might get more members helping you if you posted your pictures using
manage attachments.

I wasn't aware of that. Out of curiosity, can I ask why it matters?

[johnboy1313]

Re: Sharp LC-47SB57UT will not power on

The PS pin looks to be the one you need to look at.
Try forcing that to 5V using 5VSB with a 1k resistor.

To force the power supply on, you will need a couple of resistors. I usually use 100 Ohm resistors for this, but it is not critical, anything between about 47 Ohms and 1K Ohms is probably fine. Unplug the TV from the wall. Disconnect the cable that goes from CN903 on the power board by unplugging it from the main board. On this cable you have just disconnected, run one resistor from 5V (yellow wires) to On/Off (Blue wire), and another from 5V to PS On (white wire). Make sure this cable/resistors cannot accidentally short against anything, Plug the TV in to the wall power outlet. You should be able to read all of the power supply voltages with the unit connected in this manner. You will probably see the backlights lit too.

Thanks guys.

[ben7]

Re: Sharp LC-47SB57UT will not power on

The 0.79v on the 12v rail is odd. It could be a short on the mainoard.

If it is still like that when the PSU is powered on, while disconnected from the chassis, then there is an issue with the PSU.

[johnboy1313]

Re: Sharp LC-47SB57UT will not power on

To force the power supply on, you will need a couple of resistors. I usually use 100 Ohm resistors for this, but it is not critical, anything between about 47 Ohms and 1K Ohms is probably fine. Unplug the TV from the wall. Disconnect the cable that goes from CN903 on the power board by unplugging it from the main board. On this cable you have just disconnected, run one resistor from 5V (yellow wires) to On/Off (Blue wire), and another from 5V to PS On (white wire). Make sure this cable/resistors cannot accidentally short against anything, Plug the TV in to the wall power outlet. You should be able to read all of the power supply voltages with the unit connected in this manner. You will probably see the backlights lit too.

I'm pretty sure I followed the instructions. I used 2, 220 ohm resistors because those were the first ones I positively ID'd in the bin. Red, red, brown, gold. I confirmed it with my meter. I installed them per your directions and got a steady fluctuation from ~2.0V - ~3.5V at all four pins involved.

Long story short, when plugged back in, I still see no power at ON/OFF, either of the 12V red wires, or either of the 24V orange wires.

EDIT- in the pic it looks like the resistors may have been touching. They were not.

[johnboy1313]

Re: Sharp LC-47SB57UT will not power on

Here's another shot

[tom66]

Re: Sharp LC-47SB57UT will not power on

On some TVs, PSON needs to be brought low; try connecting through 220 ohm to ground.

[johnboy1313]

Re: Sharp LC-47SB57UT will not power on

On some TVs, PSON needs to be brought low; try connecting through 220 ohm to ground.

With the resistors in the pins below, I now have 0V at PS_ON, white, and 5V at DIM, blue but still nothing at either 24V or 12V.

EDIT- Ok, I see what I'm doing wrong. Green is ON/OFF not blue. I'll try again and post back in a second. My bad.

[johnboy1313]

Re: Sharp LC-47SB57UT will not power on

I tried 5V to ON/OFF with PS_ON to ground and again with PS_ON to 5V same results as above.

[tom66]

Re: Sharp LC-47SB57UT will not power on

OK, can you check what the voltage at PSON is each time, just to be sure the resistor is the right value. It might actually be a PSU problem -- that's something that can be diagnosed...

[johnboy1313]

Re: Sharp LC-47SB57UT will not power on

OK, can you check what the voltage at PSON is each time, just to be sure the resistor is the right value. It might actually be a PSU problem -- that's something that can be diagnosed...

With ps_on to 5v both ps_on and on/off fluctuate back and forth from 2.5v to 3.5v. With ps_on to ground, ps_on is at 0.0v and on/off is at 5v. There is no click that I've become accustomed to hearing at power on. The LED on the front never lights up.

[johnboy1313]

Re: Sharp LC-47SB57UT will not power on

Resistor 1

[johnboy1313]

Re: Sharp LC-47SB57UT will not power on

Resistor 2

[tom66]

Re: Sharp LC-47SB57UT will not power on

So, if PSON is varying, check if 5VSB is too.

[johnboy1313]

Re: Sharp LC-47SB57UT will not power on

So, if PSON is varying, check if 5VSB is too.

Yes it is.