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

[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

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.

[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?

[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

[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

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

[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

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

[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

Would that cause the PFC circuit to stay on?

[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

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

[jason123]

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

Thanks.. ALL LED strips have been replaced with a brand new set - not used set. I used the upgraded set with adhesive tape - Identical to ShopJimmy

[nomoresonys]

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

Was just looking at jjanssen7's one here: https://www.badcaps.net/forum/showth...00+current+mod

[jjanssen7]

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

That red note is interesting. $98 USD plus shipping and tax and the significant amount of labour to replace all the strips with upgraded ones means that lowering the current and replacing one or two strips is the only cost effective route for our purposes.

[nomoresonys]

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

Also talks here of a superior led: https://www.shopjimmy.com/lg-5835-w6...-strips-24.htm

[nomoresonys]

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

Check the note in red here: https://www.shopjimmy.com/lg-cov3369...wer-supply.htm

[nomoresonys]

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

I have worked on 6-7 of this model and each time replaced an LED strip that was bad. TV repaired, and then within days another strip failed and back to the blinking light on startup. After replacing a second strip, (with help from badcaps.net) I started to modify that LED driver board to send less current to the LED array, hoping to extend the life of the remaining backlights before they fail. Still testing at this point in the field, but none have come back.

What I'm saying in your context is that the next LED strip may be on its way out. Will follow this thread!

I think this is a good idea too.

[jjanssen7]

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

I have worked on 6-7 of this model and each time replaced an LED strip that was bad. TV repaired, and then within days another strip failed and back to the blinking light on startup. After replacing a second strip, (with help from badcaps.net) I started to modify that LED driver board to send less current to the LED array, hoping to extend the life of the remaining backlights before they fail. Still testing at this point in the field, but none have come back.

What I'm saying in your context is that the next LED strip may be on its way out. Will follow this thread!

[nomoresonys]

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

Test CN402 also.