Sharp lc-55le643u Dead

[Jsikora]

Hi all!
Working on this Sharp lc-55le643u that is dead. I've already used the backlight tester to verify they are all good. When testing the PS the voltage on the main caps fluctuate between 173v and 230ish. After disconecting the PS from main board however the votage stays at a constant 173v. So I am assuming problem has to be coming fromthe main board. I have heard that the lc-xxle643u main boards have had issues, not the exact model but am trying to see where to begin testing as I do not want to pay what they are wanting for these boards. Ready to start troubleshooting this one. I will get pictures as soon as I can. Just trying to see if anyone else has solved this and make it easier to begin. Thanks everyone and have a great day.

[nomoresonys]

Re: Sharp lc-55le643u Dead

Test connector from mainboard to powerboard on powerboard side with all boards hooked up, test with tv plugged in but off then hit power, report both conditions here, give pin number, pin description/name and condition both off and when you hit power on. Procedure in second link below in signature if needed. meter set at 20 vdc.

[Jsikora]

Re: Sharp lc-55le643u Dead

Connector going to main

[Jsikora]

Re: Sharp lc-55le643u Dead

The only place I get any voltage is the 3 19v pins. It does the same thing as the main caps on the PS. When main board is not connected I get steady 19V on each but with cable to main board connected it fluctuates between 17V and 19V. Makes me almost positive the problem is due to main board, but I am not sure where to begin testing on the main.

[nomoresonys]

Re: Sharp lc-55le643u Dead

Shine a flashlight on the screen hit menu see if you can see any text or anything, is there a standyby light on the front or no light at all? check tcon fuse too.

[Jsikora]

Re: Sharp lc-55le643u Dead

Shine a flashlight on the screen hit menu see if you can see any text or anything, is there a standyby light on the front or no light at all? check tcon fuse too.

No standby light, I already checked backlights with LED tester and they are all good. No change even if the T-Con is disconnected.

[nomoresonys]

Re: Sharp lc-55le643u Dead

All the tests are for a reason, so far you haven't done any of them as instructed, I don't mind helping BUT not going to have a battle over getting simple tests done, I'm out.

[Jsikora]

Re: Sharp lc-55le643u Dead

I have tested them and gave the results in the previous post. I get 19V on all 3 of the 19V outputs to the main board when it not connected to the main board and also the voltage on the caps are steady, but when connected to the main board the voltages on both fluctuate. There is no standby light and nothing on the screen with flashlight test. T-Con fuse tests good.

[nomoresonys]

Re: Sharp lc-55le643u Dead

One way to confirm powerboard and backlights is to UNPLUG cable from powerboard to mainboard, and jumpstart powerboard by itself, unless it has pullup resistors, if it has pullup resistors then as soon as you plugged in the ac the backlights should come on. I wouldn't buy a new mainboard til powerboard and backlights are proven. then if backlights come on and stay on it's likely the mainboard at fault, I'm not sure how it's done with this model tho, maybe another member has the 411.

[Jsikora]

Re: Sharp lc-55le643u Dead

OK, thanks for the info. I assume this would be done with a 1KOhm resistor??
I'll see if I can find the info on how to do this, hopefully someone else will jump in and have the answer.

[R_J]

Re: Sharp lc-55le643u Dead

You can use a 1K ~ 5K resistor. You must disconnect the main board for this test. You will connect it between +19v and PS_ON, at this point I would check the voltage on the main filter and see if it goes from 160vdc to around 300vdc. If this works I would suspect the main board is not giving the PS_ON signal.
The reason the 19v fluctuates in standby is the power supply is running in a low power state (burst mode). The main board will operate in standby with a voltage likely between 12~19 volts. Once the power supply gets the PS_ON command the PFC circuit will be turned on and supply a higher B+. The main power supply ic will operate at full and supply a more constant 19v