Philips 47PFH4109 blinking 2 times when powering

[Protker]

Hello!
So i have a Philips 47PFH4109, and when i powering on the tv just blinks once, then after a 2 seconds blinks again, and does not turning on.
I mean i measuring voltages such like 30V on the leds and the 12 volts on the other panels, which seems to be okay.
I checked the backlight no issues with the leds.
I checked every component such as all the mosfets, all the diodes, i dont see any bad capacitors (unfortunatelly i only can measure up to 200uF).
I even took out the LD7591 chip and without it doing the same as before.
Im just seeking for advice, or even someone enountered a similar problem?

Im attaching some pictures if thats help.

Thanks in advance!

[dskall]

Re: Philips 47PFH4109 blinking 2 times when powering

You are getting voltages on your mainboard?

[Protker]

Re: Philips 47PFH4109 blinking 2 times when powering

Yes i get voltages on the mainboard. Well on the power supply board is written that there should be 12V, i get 11,3 11,7V, so i assume that is ok. After powering on i measuring voltages up to 50V on the led connector, then it falls back to steady 30V. After that no nothing stays in standby mode.
I should check if i get picture when its in standy mode no?
Thanks

[Protker]

Re: Philips 47PFH4109 blinking 2 times when powering

So there is screen, only the backlight is missing.
I have to say i tried to light up the backlight applying dc on the led connectors and around 50V it lights up both led strip nicely. This is the reason im assuming the strips are good.
Maybe the supply board sensing that too much current was drawn by the strips and shuts off the backlight?

[dskall]

Re: Philips 47PFH4109 blinking 2 times when powering

So you have image. On power board do you have a BL_on? Should have voltage on that terminal. Probably bad LED.

[R_J]

Re: Philips 47PFH4109 blinking 2 times when powering

You likely have a bad led in one of the strings, if the current draw for the string is wrong, the tv power supply will detect that and shut down. I suspect one led is shorted and supplying a voltage from a bench supply will not detect the bad led but light the others in the string.

The LD7591 is for the pfc circuit not for the led's

[Protker]

Re: Philips 47PFH4109 blinking 2 times when powering

Thank you for all the comments and suggestions, i will tear down the tv as soon as i will have time for that, and will give you a feedback. Thanks!

[Protker]

Re: Philips 47PFH4109 blinking 2 times when powering

So im back, i tested the leds, every led strip is lights up nicely. I assembled the tv back again. Im starting to suspect maybe a capacitor lost its capacitance, and causing the trouble here? Primarily the ones in nearest to the led connector?

[dskall]

Re: Philips 47PFH4109 blinking 2 times when powering

How did you test led's?

[Protker]

Re: Philips 47PFH4109 blinking 2 times when powering

I disassemled the whole tv took out the screen and applied dc to the strips.
I will try tomorrow to test the capacitors.

[Protker]

Re: Philips 47PFH4109 blinking 2 times when powering

So i tested out the capacitors, all showing the right parameters(what is written on the caps). I found the exact schematics on the net, and according to the schematics everythings is fine.
The problem is whenever i turn on the tv, it flashes 2 times(trying to light up the backlight), but unfortunatelly gives up and after these 2 try remains unlighted (i have screen logo etc btw).

[vinceroger69]

Re: Philips 47PFH4109 blinking 2 times when powering

I disassemled the whole tv took out the screen and applied dc to the strips.
I will try tomorrow to test the capacitors.

just a thought, although the led strips light up using dc volts one strip maybe using more amps which maybe putting the set into protection mode
the latest led testers show voltage and amps
https://www.ebay.co.uk/itm/273214652...3ABFBMxK_Yo8Bf

[dskall]

Re: Philips 47PFH4109 blinking 2 times when powering

Will led's come on with t-con disconnected?

[Protker]

Re: Philips 47PFH4109 blinking 2 times when powering

Nope, with disconnected tcon remains the same.. I measuring the +30VDC before the step up converter, seems that maybe the converter chip doesnt doing its job properly (PF7903BS) Sadly i cannot find any kind of data of this chip, so i can temper maybe with the feedback leg or ovp leg, to make it work...

[Protker]

Re: Philips 47PFH4109 blinking 2 times when powering

Hello guys again. I managed to solve the backlight issue with this tv.
So i managed to take out the mosfet (in the datasheet is Q8104) and i figured out even though it was not shorted, but i couldnt open the fet with multimeter.
So I searched for a replacement and i found a random fet which had the same pinout. And it worked, lighted up the strip nicely. After i made sure that the mosfet is the problem i searched for a better replacement bc the random i found had 5ohm rds on resistance.
So i placed an IRF 540 and stopped working..
Hm.. then i found out if i decrease the resistance of the R8117 resistor from 7,5k to lets say 5,6k, then i can trick the ovp/dim pin of the PF7903BS chip. And thats that.
Thanks for the help and the suggestions!

[dskall]

Re: Philips 47PFH4109 blinking 2 times when powering

Nice job.