Philips 50PUT6400/12 no backlight

[notallbad]

Mains power on the front panel red LED comes on solid then slowly 'flashes' about 80 times, (more like it slowly dims out and brightens back up), then goes back to solid red.
Bring out of stby the red led flashes 3 times quickly then goes out, the 'Philips' front panel display sign lights up.

Get sound and can change source etc... there is a picture visible with a flashlight.

The backlight does NOT light up nor does it briefly light up before going out. This is when viewing from the front and from the rear with the back cover removed.

Voltage readings as follows with reference to chassis gnd: (<<in stby>>, <<On>>)

BL_Off/On (0v , 3.1v)
3D_On (0v , 0v)
gnd
gnd
+12_A (0v, 11.7v)
+12 (0v , 11.7v)
+12 (0v , 11.7v)
+5/+3.5v (3.5v , 3.5v)

DIM (0v , 1.4v)
PS-ON (0v , 3.3v)
gnd
gnd
+12v_A (0v , 11.7v)
+12v (0v , 11.7v)
+12v (0v, 11.7v)
+5v/+3.5v (3.5v, 3.5v)

With LED's connected or disconnected both +VLED pins rise to 75v, settle down to 72v, 5-10secs later ramps up to 102v then gradually drops out to zero.

Both -VLED1 and -VLED2 read 0v when LED's connected or disconnected.

I think its looking like open circuit LED's but just wanted to be sure I am not missing anything before proceeding with the onerous task of disassembling the display panel.

Photos of Panel details and LED driver/PS board.

[notallbad]

Re: Philips 50PUT6400/12 no backlight

PS Board connector close ups.

[budm]

Re: Philips 50PUT6400/12 no backlight

The -VLED's are measured against circuit GND?
What are the Voltage rating of those 3 lytics caps in that LED driver section?
BTW, your pictures are way out of focus.

[notallbad]

Re: Philips 50PUT6400/12 no backlight

The pair of caps are 120uF 160v and the single cap 39uF 160v.

What point should I use for circuit gnd? On the COLD - Secondary side, of course.

[budm]

Re: Philips 50PUT6400/12 no backlight

Chassis GND.

[notallbad]

Re: Philips 50PUT6400/12 no backlight

Yes, using chassis gnd.

[notallbad]

Re: Philips 50PUT6400/12 no backlight

Photos

[notallbad]

Re: Philips 50PUT6400/12 no backlight

So is this an LED replacement job?

[vinceroger69]

Re: Philips 50PUT6400/12 no backlight

have you got a led tester if so do the leds light up?

[notallbad]

Re: Philips 50PUT6400/12 no backlight

Don't have an led tester though gonna get one!

[vinceroger69]

Re: Philips 50PUT6400/12 no backlight

i would wait and see what budm thoughts are regarding the led voltages before you strip the lcd panel down.
It looks like this tv uses 64 leds roughly 192 volts in total or if 72 led version 216 volts
https://www.ebay.com/itm/Vizio-TPT50...-/252451628853

[notallbad]

Re: Philips 50PUT6400/12 no backlight

I think it may be the 72 led version, not sure.

But yes, hopefully budm will come back and advise further.

Thanks.

[budm]

Re: Philips 50PUT6400/12 no backlight

OK, the LED power supply does not use Boost converter circuit, so 102V reading is about right with 160VDC rating caps.
The panel has 3 LED strings, two of them are connected in parallel as you can see that it has two read wires go to one terminal, and then two black wires go the another one terminal.
It is also more like likely to be 72 LED's, so 72 /3 strings = 24 LED per string, so the Vf at 3V for 24LED = 72V total Vf for the LED string + Vrops on that PWM control (you can see two small heatsinks).
So What you can do is to use 180 ~ 220 Ohms 5W resistor between V- and chassis GND one V- at at time to see if the Backlights will flash on for seconds or not. If you do not have resistor you can use 10W or 25W (not more) in place of the resistor to test.

[notallbad]

Re: Philips 50PUT6400/12 no backlight

Quote "If you do not have resistor you can use 10W or 25W (not more) in place of the resistor to test."

Is this meant to have said 10w or 25w lamp/bulb (not more) in place of the resistor to test?

Thanks budm

[budm]

Re: Philips 50PUT6400/12 no backlight

Sorry, 230V 10W or 25W incandescent lamp.

[notallbad]

Re: Philips 50PUT6400/12 no backlight

Decided to buy a GJ3C Led tester.
Found that led's were not lighting so stripped it down. Tested led's individually to find about 5 open circuit.

Now to find suitable replacements.

The meter reads 2.4/2.5v so clearly need 3v leds.

Dimensions are approx. 3mm x 3mm x 0.5mm (l, w, h). With a 2mm diameter lens.

Where I do have difficulty is knowing the lux range, do they need to be in the 5000 range soft white/neutral, presumably warm or cool white will give a spot effect on the screen.

[notallbad]

Re: Philips 50PUT6400/12 no backlight

Removed led from panel.

[vinceroger69]

Re: Philips 50PUT6400/12 no backlight

if you send this ebay seller a message im sure he will help you hes very helpful and a lot of us on here use his shop https://www.ebay.co.uk/usr/microtech...88.m1543.l2754

[budm]

Re: Philips 50PUT6400/12 no backlight

Do you have picture of the bacside of the LED showing the solder pad pattern? You also need to find out if the big pad is Anode or Cathode.

[vinceroger69]

Re: Philips 50PUT6400/12 no backlight

sorry please ignore i thought i had some 3030 led but didnt there are larger sorry