LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

So transfered the good zener from good board to bad. Now bad board reads 23k across hot opto side. TV powered up for 3 seconds then off. Something else is a problem.

Disconnected LED Connector (to exclude these caps) and no change. I don't think these caps are to blame. Took them off voard, and did ESR and C measurements. No significant difference

so it powered off in 3 seconds, was that with the cable from powerboard to mainboard unhooked?

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

so you tested the pins of those 2 ic's to make sure both boards give the same readings? and tested all the transistors including the little ones standing by themselves?

tested is "loosely used".. yes, I spot checked continuity and impedance checks on the ICs. Small BJTs are fairly similar.. some read 50M, others read Open.. yet, test again and you get open on both.. so very subtle differences. The only smoking gun thus far is the zener diode and I have one on order.

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

so it powered off in 3 seconds, was that with the cable from powerboard to mainboard unhooked?

No, that's with all the cables connected.

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

does the tv work ok with the new powerboard?

[R_J]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

So transfered the good zener from good board to bad. Now bad board reads 23k across hot opto side. TV powered up for 3 seconds then off. Something else is a problem.

Disconnected LED Connector (to exclude these caps) and no change. I don't think these caps are to blame. Took them off voard, and did ESR and C measurements. No significant difference

If the zener diode on the bad board was bad, transferring a good diode from the good board may not fix the problem because the opto or something else may have been damaged. Did you measure the voltage across the zener diode?
What was the number on U1?

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

does the tv work ok with the new powerboard?

seems to work fine. Yes

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

If the zener diode on the bad board was bad, transferring a good diode from the good board may not fix the problem because the opto or something else may have been damaged. Did you measure the voltage across the zener diode?
What was the number on U1?

No, I didn't measure the voltage. But the impedance of the node with the Zener in place is 2.3k, while the good board has 23k roughly. When I remove the zener on the bad board, the impedance measures closer to 23k.

One IC was the OZ9906GN, and the PFC is TEA1716T

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

ok, maybe replace that opto if you have one handy.

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

ok, maybe replace that opto if you have one handy.

Ordered both the zener and the Opto.. replaced the zener first and that did the trick. TV is up and running. I don't think I need to replace the opto if it's working.

Theory here is maybe I had zener and one/both of the ICs bad.. replacing them all took care of the issue.
Or just "Zener" decided to go bad??
Hope this helps someone fix these expensive boards.

Thanks for the help

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

Glad to hear it.

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

so to be clear, it DID NOT work when you transferred the zener to the old board BUT the new zener you ordered did work?

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

so to be clear, it DID NOT work when you transferred the zener to the old board BUT the new zener you ordered did work?

I did 2 things.. replace the zener with a new one and touched up all the IC pins. I did see under a microscope that some pins, one in particular, didn't seem to be soldered all that well.

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

ok thanks for clarification, another nice save.

[jason123]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

ok thanks for clarification, another nice save.

Thank you for the help

[AFVet]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

Jason
I am having some issues with my power board also. The information you posted and so diligently troubleshot definitely was beneficial to me. I haven't quite figured it out, but after the last test with the TV is miraculously started working when power on through the remote. So I am going to leave it alone now. I went through with my magnifying glass on solder joints, removed CAPs for value, tested the transistors, checked backlights. All seemed to be working and put it all back together and the TV came up, so I am not sure what fixed it.

Thanks for the information you posted here.

[nomoresonys]

Re: LG 50UH5530 Turns Off And Wont Turn On: diagnoses included

AFVet, I think it must have been a bad solder joint.