SHARP LC-40LE814E turns off after 20min

[Fritz23]

Hey guys,

I've got a SHARP LC-40LE814E with a DPS-126CP power supply.
The problem is, that the TV turns on, shuts off after 20 min and after ~3min turns on again.

The only fault I could imagine is a bad solder joint or an overheating problem, so I resoldered pretty much every big through hole part on the PSU. I still need to check if it solved the problem but since I suspect it didn't solve the problem I wanted to ask here what to check next/first.

The voltages should be all okay, since it works the first 20 min. I can't see any obvious faulty capacitors. Could the mosfets be overheating?

Regards

[rievax_60]

Re: SHARP LC-40LE814E turns off after 20min

I had that symptom with a similar sounding model. I found it to be caused by deteriorating
opto-couplers in the power supply. I could cause the TV to shut down sooner by warming the optos with hot air.
Can you post some photos? I might recognise the board. It has been over a year ago.

[Fritz23]

Re: SHARP LC-40LE814E turns off after 20min

Thanks for your answer.

Here you have the front and the back of the PSU. Sorry for the bad lighting

Heating the four optos seems to be a good idea and I'm gonna try it as soon as possible.

[rievax_60]

Re: SHARP LC-40LE814E turns off after 20min

For more detail, see these threads, https://www.badcaps.net/forum/showth...ght=68k&page=2
Be wary, I made a reference to a wrong resistor somewhere in there which is corrected later.

[Fritz23]

Re: SHARP LC-40LE814E turns off after 20min

I soldered in the temporary 68k resistor. It seems that it solved the problem.

Tomorrow the new optocouplers will arrive and I think that'll be it. Should I remove the resistor afterwards or leave it there?

Thanks rievax_60!

[rievax_60]

Re: SHARP LC-40LE814E turns off after 20min

The resistor can stay. I hope there was a mention about how to pick replacement optos in those threads. There is a wide range in the CTR spec, and usually grouped with a suffix on the part numbers. Like A, B or C. Most applications don't care about this.
The CTR of the opto in the backlight circuit can cause problems like backlight flickering. It is the opto that is on its own. Make certain that the backlight adjusts smoothly over its whole range without any flickering.

[Fritz23]

Re: SHARP LC-40LE814E turns off after 20min

I think they picked a SHARP PC817. That are the ones I have ordered.
If I get any flickering should I go for an original Cosmo K0101 opto or just solder in the old one? The old backlight opto should be okay right?

I see right now the Cosmo optos have CTR-rank H and the Sharp optos have CTR-rank C. I'm excited how it will work out.

[rievax_60]

Re: SHARP LC-40LE814E turns off after 20min

The original optos fail by gradually decreasing CTR. Adding that resistor compensates for the decrease of the CTR of the opto in the AC_DET circuit.
My TV started flickering about a month after fixing the first problem. The flickering is caused by the opto in the backlight circuit decreasing its CTR. There is a trimpot on the LED side of this opto to compensate for a wide range of CTR.
Afaik, there is no documented procedure for adjusting this trimpot and the other one near it. I left the other one near it alone.
The flickering is most likely to occur at low BL setting and when the opto is warm.

[Fritz23]

Re: SHARP LC-40LE814E turns off after 20min

Okay, thanks.

Until now it works like a charm. I'll keep this in mind.

[Fritz23]

Re: SHARP LC-40LE814E turns off after 20min

Hi again!

I'm back with the same TV. This time it doesn't turn on at all and is just blinking two times.
I checked the voltages on the PD connector in the first seconds after hitting the power switch:
(PD-1-2)UR13.2V(SIGNAL): 12.9V
(PD-3-4)S13V.2(AUDIO): 12.9V
(PD-5-6)SGND(AUDIO): 0V
(PD-7-8)SGND(SIGNAL): 0V
(PD-9)AC-DET: 3V
(PD-10)PS-ON: 3V
(PD-11)BU5V: 5V
(PD-12)PNL-POW: 0.1V

After a few seconds the board goes into standby.
I also checked the pnl12v rail. With the TCON connected the voltage is around 7V. Disconnecting the two cables at the bottom didn't change anything. If I disconnect the TCON the voltage is around 12-13V.
I managed to turn the backlight on by pressing V-, CH+ and Power. It stayed on and interestingly the Led on the mainboard flashed some kind of an error code. 20 times slow and 16 times fast.
But since the two flashes indicate a 13V error I guess it's the first thing to check, but where do I start? In another thread I found a faulty Q7909 voltage regulator. Could that be the case here?

Btw: the resistor fix is still installed and the optocouplers have been changed again.

Regards

[dskall]

Re: SHARP LC-40LE814E turns off after 20min

Probably short on t-con

[attainteddragon]

Re: SHARP LC-40LE814E turns off after 20min

disconnect the panel from the t-con and check the 12v. just to make sure that it is the t-con and not the panel.

[budm]

Re: SHARP LC-40LE814E turns off after 20min

'(PD-12)PNL-POW: 0.1V' The main board is not sending the command signal to turn the switch that supplies the 12V (PNL-12V) to run the T-CON board.
Now are you sure that there is no PNL-POW because you indicated you do have 7V at the PNL-12V pin? For the 7V to be there the PNL-POW must be present, and the common failure for getting only 7V instead of 12V is due to bad LDO switched 12V regulator. Please verify your Voltage readings.

https://www.badcaps.net/forum/showth...602#post592602

[Fritz23]

Re: SHARP LC-40LE814E turns off after 20min

The detailed error code is a 2-5.

'(PD-12)PNL-POW: 0.1V' The main board is not sending the command signal to turn the switch that supplies the 12V (PNL-12V) to run the T-CON board.
Now are you sure that there is no PNL-POW because you indicated you do have 7V at the PNL-12V pin? For the 7V to be there the PNL-POW must be present, and the common failure for getting only 7V instead of 12V is due to bad LDO switched 12V regulator. Please verify your Voltage readings.

https://www.badcaps.net/forum/showth...602#post592602

Directly after switching the power switch on:
PNL12V: 12. 93V
PNL-POW: 0.12V

After around 8 seconds (assuming the TV is trying to start):
PNL12V: 7V
PNL-POW: 3.23V

Then it starts displaying the error code :
PNL12V: 4.28V
PNL-POW: 0.1V

disconnect the panel from the t-con and check the 12v. just to make sure that it is the t-con and not the panel.

Tried that already. It's still 4-7V

Is there a way to check if it's the PSU or the TCON? Apply external 12V?

[attainteddragon]

Re: SHARP LC-40LE814E turns off after 20min

'(PD-12)PNL-POW: 0.1V' For the 7V to be there the PNL-POW must be present, and the common failure for getting only 7V instead of 12V is due to bad LDO switched 12V regulator.

https://www.badcaps.net/forum/showth...602#post592602

sounds like bud knows what to look for.

i believe that a pic of the main board is now needed to continue.

[dskall]

Re: SHARP LC-40LE814E turns off after 20min

You say you have 12v if you disconnect t-con. So you either have a short on t-con or 12v output cannot maintain load