LG 65UH5500-UA Backlight flash on first power up only

[nomoresonys]

Re: LG 65UH5500-UA Backlight flash on first power up only

That symptom described in first post seems like a faulty cap or a iffy solder joint, maybe try hitting your boards with a hairdryer when it's acting up, see if it changes any, heat any caps that could be the culprit, could be you have one that's just a little weak.

[jason123]

Re: LG 65UH5500-UA Backlight flash on first power up only

Would that cause the PFC circuit to stay on?

[nomoresonys]

Re: LG 65UH5500-UA Backlight flash on first power up only

with tv unplugged from outlet, unhook all connectors from powerboard, plug power cord back into outlet, see if you still have 385 with powerboard by itself.

[jason123]

Re: LG 65UH5500-UA Backlight flash on first power up only

Confirmed.. 385v is present with nothing but AC cable connected. The PFC is the TEA1716T from NXP

[budm]

Re: LG 65UH5500-UA Backlight flash on first power up only

The PFC boosted Voltage will be present when PS-ON is present, so check and see if the PS-ON is >2V when running the power supply board by itself, if it dies then it may have pull-up resistor for self test function on the PS-ON pin.

[jason123]

Re: LG 65UH5500-UA Backlight flash on first power up only

The STB (PS-ON) has 0.017 V and the large caps have 384 V today

[nomoresonys]

Re: LG 65UH5500-UA Backlight flash on first power up only

The STB (PS-ON) has 0.017 V and the large caps have 384 V today

Is that reading with all boards hooked up?

[jason123]

Re: LG 65UH5500-UA Backlight flash on first power up only

No, just the power supply board connected to AC.. no other cables connected to the power board

[budm]

Re: LG 65UH5500-UA Backlight flash on first power up only

So if you have all the board connected, does STB pin of the power supply change state and TV is toggle on and OFF?

[budm]

Re: LG 65UH5500-UA Backlight flash on first power up only

I look at your post #20:
I took the measurements on CN2. The issue i see is the larger cap has 385V all the time, even when cable CN402 Is not connected... PFC circuit or what is suggested?
STB is 3.4V,
13.2v are 13.15 (when backlight is on), 12.6v when it doesn't turn on
FAIL is 0.057
80v are 77.8V

But now you are saying that the STB is <1V when not connected.

[jason123]

Re: LG 65UH5500-UA Backlight flash on first power up only

Stb is < 1 v when the connector is not plugged in. I believe the voltage is driven from main board on Stb. Post #20 is with everything connected. I just noted the large cap voltage when connected or not connected

[budm]

Re: LG 65UH5500-UA Backlight flash on first power up only

So does the STB change state when TV is turned on and off with everything connected?
Yes the main board control the STB signal.
The STB control is being routed through the LED driver board.

[jason123]

Re: LG 65UH5500-UA Backlight flash on first power up only

With everything connected.. StB is 3.4 v when tv is on and 0.057 when tv turns off

[budm]

Re: LG 65UH5500-UA Backlight flash on first power up only

So to be clear, when the TV is OFF, the Voltage on the main cap stay at 385V?

[budm]

Re: LG 65UH5500-UA Backlight flash on first power up only

At this point , the FAIL pin is the issue since you have to GND it to get the TV to come on, need to trace out the FAIL pin to see where it leads to as RJ suggested.
https://www.shopjimmy.com/lg-cov3369...er-supply.htm#
https://assets.shopjimmy.com/media/c...401-bottom.jpg

[jason123]

Re: LG 65UH5500-UA Backlight flash on first power up only

Not anymore. Recall i replaced the full LED Set and fail signal is 0 v

[jason123]

Re: LG 65UH5500-UA Backlight flash on first power up only

So to be clear, when the TV is OFF, the Voltage on the main cap stay at 385V?

Correct...

[jason123]

Re: LG 65UH5500-UA Backlight flash on first power up only

Is it the NXP Pfc IC, or...

[jason123]

Re: LG 65UH5500-UA Backlight flash on first power up only

So I replaced the IC.. same issue - with only AC connected to the power supply, I see 385 V across large caps, and 0 V on STB pin

Bought another power supply board - it's acting exactly the same 382 V across large caps with only AC connected. Could it be that both boards are bad? or are they supposed to work this way??

[budm]

Re: LG 65UH5500-UA Backlight flash on first power up only

Edit: Looking at the spec sheet of the SMPS/PFC IC combo, the PFC has enable pin 22 (see page 34).
OPTO IC 1 looks to be for the PS-ON controller OPTO.
BYW, are the 80V and 13V present when running the power supply board by itself?
The key point right now is that if you do have the 80V output of the power supply board to feed the LED driver board with Error pin is LOW, and the LED driver board has all the control signals then the back lights should be on.