RCA LED60B55R120Q Shuts Down

[ljintexas]

This set shuts down on it's own after 10-15 min with rear cover on. Will run for days with rear cover off. If I cycle power, it will fire back up for another 10-15 min.

[ljintexas]

Re: RCA LED60B55R120Q Shuts Down

Upon further investigation, through using a heat gun and two different power supplies, I have localized the issue to the power supply. Sometimes only backlight driver section dies even though BL_ON is still getting signal from main board..audio continues, still have 12 volts..other times 12 volts drops out and kills everything. I still have 5 volts stdby when 12 volts dies.
Both LED driver circuits read the same voltage to the tenth of a volt(157.1). Main Cap reads 306 volts when set is running.

[nomoresonys]

Re: RCA LED60B55R120Q Shuts Down

Main cap is 306v and you have a good picture display or do you mean when it acts up?

[R_J]

Re: RCA LED60B55R120Q Shuts Down

Check the power supply ON/OFF pin, The standby +5vsb, +5v, +12v come from the same power supply section, but the +5v & +12v are switched, so it seems they are being turned off when the fault happens. If the ON/OFF signal is lost this also turns off the pfc circuit dropping the main cap voltage from 305vdc to 160vdc
I would also check the solder connections on the transformers and any of the transistors mounted on heatsinks.

[ljintexas]

Re: RCA LED60B55R120Q Shuts Down

Main Cap is 306 when working properly. I re soldered every power passing device and contact on the power supply, including all three transformers..Been running out in the shop for an hour with the back panel on and it's 75F here today..Before within 15 min it would turn off with back panel in place and it was 50F.

[ljintexas]

Re: RCA LED60B55R120Q Shuts Down

Well I just lost back light driver section still have 2.5volt ON/OFF and 5 volt BL_ON signal as well as audio. All 5 volt and 12 volt voltage is still intact. I can even turn it off, then back on and regain audio. I have read these sets are bad about LEDs failing. Could bad LEDs be overloading the driver circuit causing the overheat condition?Is there a way to test them without exposing them? I can access them from the rear of this set without having to remove the LCD panel.

[R_J]

Re: RCA LED60B55R120Q Shuts Down

You can have one or more led's shorted, this keeps the string intact but draws more current and the led driver goes into over current protection. or sometimes the led's go intermitint and open, they do get quite hot, and the driver goes into over voltage protection.
There is no real way to check them without exposing them, even a led tester might show them as good as they are intermitint.

[ljintexas]

Re: RCA LED60B55R120Q Shuts Down

It must be going into over current protection as you say. I left it with 120 volts applied and let it get stone cold. Turned back on and still no back light driver. If I remove 120 volts for 15 sec and restart, back light comes back. Cycling power is resetting protection circuit.
I will be exposing LEDs next. Thanks RJ!

[neilc6]

Re: RCA LED60B55R120Q Shuts Down

RCAs have high rates of backlight failures because the default setting in Standard picture mode sets them to 100%. The backlight level can only be changed in the service menu under Panel Settings. menu-1-1-4-7 or source-2-5-8-0. Depending on the model, the backlight level will apply only to the currently selected input or be saved under User picture mode.

[ljintexas]

Re: RCA LED60B55R120Q Shuts Down

I will change the setting once I replace the arrays.
Thank You for the tip!!

[ljintexas]

Re: RCA LED60B55R120Q Shuts Down

Replaced LED arrays. Entered the Service menu via menu1147. Backlight was set to a default of 0. I adjusted it to a level of 4. I read in another bulletin that lower number = brighter setting. Could not find a setting that says "backlight level normal" in the service menu. Set worked for 4 hrs without losing backlight.