Sharp LC-80LE757U - Click - shuts off

[jason123]

Hi there,

Hopefully someone has some experience with this TV - yes, it's a mammoth 80" in decent shape other than the plastic falling apart where the screws attach the back cover to TV.

So, when I got it, the TV simply clicks almost every few seconds, small click then another (relay actuating and disarming)

I disconnected LEDs to power supply, and the same clicking. Clicking goes away when i disconnect the mainboard (as nothing is turning the TV on)

I started disconnecting the IR, Wifi,.. to the Main board, and voila.. the TV starts up, I can see beautiful screen with menu and backlight, then it dies (clicks) again, and the cycle continues. I can connect all cable to main board again and it does the same cycle. Seems like it just needed a little push to get in the starting up mode.

I'm guessing there is a deterioration to the power supply board, causing it thermal / over-current shut down. All rails seem to come on on the power supply with the "On" click happens for few seconds. PNL12 V is running at 11.74 V. UR13.2 is running at 13.03 V. 5 is running at 4.92 V.

Thoughts?

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

Weak capacitor? maybe try hitting the caps with some heat, see if anything changes.

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

Weak capacitor? maybe try hitting the caps with some heat, see if anything changes.

Thanks nomoresonys .. would that show up as a cap with high ESR? should I start there maybe?

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

Yes, if the heat decreases the esr and tv starts working, you found a bad cap, can add a little heat to the little blue ceramic caps too, looks like a reddish colored ceramic cap there by the sticker, a hair dryer works pretty good for testing. Might be a different problem but that test is easy and don't require a lot of labor.

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

You're right on my friend.. TV works beautifully with blow drier aimed at the area. Now pinpointing that cap is a challenge. I can find all the caps in the region on Digikey, but that red one, how would you test that?? it's a poly film of some sort.

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

Hmm, you said big tv with crumbling plastic, might be best to replace all the electrolytic caps in that area so you don't have to go back in there, the ceramics are more robust, they might be ok, those polyfilms do go bad, might be a good idea to replace or test on a esr meter.

[budm]

Re: Sharp LC-80LE757U - Click - shuts off

Verify that the AC_DET signal is OK or not when it acts up,

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

Verify that the AC_DET signal is OK or not when it acts up,

AC_DET does not seem to be holding at 3.3 V.. it's running at 0.5 V, then spike up then down..

[budm]

Re: Sharp LC-80LE757U - Click - shuts off

That is the problem, more likely the Opto couple problem in the AC_DET circuit.
When you heat up the power supply board you need to do localize heating, may be you ending up heating the opto.
The standby Voltage, PS-ON, ect. are stable for sure, correct?

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

The BU5 is the one I looked at and it's solid at 4.92 V. The PS_ON coming form the Main board is stable, but it goes away as soon as STB shuts off.. so it follows it. Any idea which is the OPTO for the AC_DET? or do I need to follow the trace from the connector? Thanks

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

Any guidance on resolving this issue, budm, or anyone who's experience with the AC_DET troubleshooting, would be greatly appreciated! thank you

[budm]

Re: Sharp LC-80LE757U - Click - shuts off

Since you are able to heat up the power supply board and able to get the TV to work, so just try heating up just the Opto's only and see which one will make the TV working again.

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

Thanks.. I used a blow drier and the optos are so close together that focusing on just one at a time may not be possible. I may have to trace the connection to a specific opto. I tried continuity test (since I don't have access to traces (single layer board) with board installed), but wasn't able to find the direct connection (from AC_DET to any of the opto pins in the COLD side)

The question is.. is the Opto circuit a simple current path from AC (or rectified) that pumps into the LED part of the opto and AC_DET is just the other side of the opto or is there more to the circuit? Could it be something else in the path? Because if not, then I can go ahead and replace all the opto couplers on the board for ease of fix implementation.

[jetadm123]

Re: Sharp LC-80LE757U - Click - shuts off

With the power supply unplugged, you can try to isolate the offending opto by cutting out a small piece of metal from an aluminum soda can. Place the metal over an opto and hold one end with your pliers and the and place your soldering iron tip over the aluminum piece. Once the opto is warm enough you can plug in the supply and give it a go. There are also several YouTube vids on how to check opto's. And of course there's the shotgun approach, which is replacing all 3 opto's. They are readily available and cheap.

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

Thanks jetadm123... all very helpful and I can try the aluminum piece trick.

I guess I wanted to be sure it's the Opto failing and not another peripheral that's in the AC_DET circuit.. I'm not sure what the circuit looks like as I haven't been able to find a schematic. I could reverse engineer it I guess too.

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

replaced all 3 Optos, and no change. I tracked the AC_DET to the first opto on the right, but that didn't do it, so I replaced all 3, and no luck. Thoughts?? I can't seem to heat up one component and get it to behave, but if I heat up the whole area, it seems ok.

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

I would like to work on this power supply board out of the TV, as I received a replacement power supply board and the TV is working fine. I tied PS_ON, and PNL_POW to STB, but the relay is not clicking (turning on). Do I need to connect anything else to get the board to turn on so I can troubleshoot this? Thanks

[budwich]

Re: Sharp LC-80LE757U - Click - shuts off

ok... so you now have a working board and tv. maybe not "zipped up"? with the power off / disconnected, take some "strategic resistance" measurements of the two power cards to see if you can spot anything (ie. capacitor, resistor, switching ic /fet) to narrow down your effort.... and then go watch the big tv ... :-)

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

Thanks budwich :-)
I couldn't really spot any differences worth nothing. resistors are off, some higher, some lower by 1% or so. TV is awesome!

[jetadm123]

Re: Sharp LC-80LE757U - Click - shuts off

Possibly a bad solder joint?