Phillips TV no backlight

[DjKrish]

I have a 55 inch Phillips TV thats powering up just fine but no voltage on the socket thats connecting to the LEDs. I have used a torchlight to the screen and theres image on the screen. So its clearly the LED voltages missing. When i use a multimeter to measure the voltage, the voltage starts high and then fades to zero voltage. Weird. A sign driver IC failing? I have tried high and low to find the service manual but failed. Anyone happens to have a service manual for this?

PS : Ive tried another power supply borrowed from a friend and the panel works fine.

Model Phillips 50PFA4500S

[Andrew F. Ali]

Re: Phillips TV no backlight

If the LED backlights have failed, it is normal for the Driver to send 'high' voltage to the connector pin/s at start-up and if it does not detect a load fade to 'zero'. So this is an indication the Driver is good. It seems far-fetched that 'another power supply borrowed from a friend' makes the panel work fine.

[steviewonder]

Re: Phillips TV no backlight

+1
I agree with Andrew.that is a classic sign of a L.E.D failure.,at least with every other set i have repaired...(thousands)...

[DjKrish]

Re: Phillips TV no backlight

Ok, you claim that way. I unplugged the back light cable from the SMPS, the voltage still dropping and fading to zero when plug in power. Why is that? Why when i try another similar power supply, the LED is fine? Ive even opened up the panel to see if any LED failed, all seems working fine.

[Andrew F. Ali]

Re: Phillips TV no backlight

The driver is not detecting a load and therefore will go into protect mode as it would do if the led strings are open circuit.

[dick_barton]

Re: Phillips TV no backlight

Ok, you claim that way. I unplugged the back light cable from the SMPS, the voltage still dropping and fading to zero when plug in power. Why is that? Why when i try another similar power supply, the LED is fine? Ive even opened up the panel to see if any LED failed, all seems working fine.

So you are saying that with the original power supply, the backlights do not come on but when you try another power supply the backlights work.
Are the two power supplies identical. If not, what is the part number of the power supply.
Do you have pictures of the original power supply
What is the part number written on the original power supply.

[DjKrish]

Re: Phillips TV no backlight

So you are saying that with the original power supply, the backlights do not come on but when you try another power supply the backlights work.
Are the two power supplies identical. If not, what is the part number of the power supply.
Do you have pictures of the original power supply
What is the part number written on the original power supply.

YES. Its from the same model TV.

[dick_barton]

Re: Phillips TV no backlight

If your power supply is model 715G6338 then schematic found on page 33 of the attached manual.

What are the voltages on the 3 pins of DP8101

[DjKrish]

Re: Phillips TV no backlight

If your power supply is model 715G6338 then schematic found on page 33 of the attached manual.

What are the voltages on the 3 pins of DP8101

I dont see DP but i see D8101. Is that it?

[dick_barton]

Re: Phillips TV no backlight

I dont see DP but i see D8101. Is that it?

Mistyped, yes D8101

[nomoresonys]

Re: Phillips TV no backlight

Did you check the voltages of the 2 filter capacitors, in standby and tv powered on? in the HIGH VOLTAGE/HOT SIDE.

[DjKrish]

Re: Phillips TV no backlight

I managed to replace the led driver IC, it worked, there was picture light and everything. for 1 minute. Then the IC died and back to no light and no voltage

[dick_barton]

Re: Phillips TV no backlight

What were the results of:-

What are the voltages on the 3 pins of D8101

Did you check the voltages of the 2 filter capacitors, in standby and tv powered on? in the HIGH VOLTAGE/HOT SIDE.

[DjKrish]

Re: Phillips TV no backlight

What were the results of:-

I was just about to check the voltages, the D8108 diode left and right leg had 35V and middle voltage was dropping. The i switched off the power supply and switched on again, the light is back. I was like what?

The led backlight legs (Red Pin) has 70V each on both red cables.

Update, after a few switch off and on, now the voltage disappeared. The D8108 has no voltage. 0 Voltage. Looks like something is not right. I have already resoldered all the smd and thru hole components. No cold joints.

[DjKrish]

Re: Phillips TV no backlight

After soldering a few smd components. The backlight is stable at every on and off. Led output Voltage is stable at 70.1V. When i put to standby, voltage goes to zero. When i turn on again, backlight comes on, voltage steady at 70.1V

If i keep it on standby like 10 or 20 mins and then turn on again, the backlight fails again to turn on as theres no voltage. So this time i tried probing where the voltage stops, i use my digital multimeter on AC mode and stick the black to ground and the red to one of the resistor thats R9103 leg as in the picture, suddenly the backlight comes back. Now isn't thats weird?

If i kept it turned on with the backlight, it works for hours without any problem. Sounds like it needs a kickstart.

[dick_barton]

Re: Phillips TV no backlight

Check the values of the following components are within specification
R9101 1M +/- 1%
R9102 1M +/- 5%
R9103 1M +/- 5%
R9104 22K +/- 1%
C9101 10nF
C9102 100nF

and also the solder connections of IC9101

[DjKrish]

Re: Phillips TV no backlight

Check the values of the following components are within specification
R9101 1M +/- 1%
R9102 1M +/- 5%
R9103 1M +/- 5%
R9104 22K +/- 1%
C9101 10nF
C9102 100nF

and also the solder connections of IC9101

R9101 1M +/- 1% - 984M
R9102 1M +/- 5% - 984M
R9103 1M +/- 5% - 943M
R9104 22K +/- 1% - 19.9K
C9101 10nF - 8.86NF
C9102 100nF - 105NF going down really slow 1 by 1 digit

IC9109 has been replaced with new IC.

When turn on for the very first time for the day, it works. Standby and turn on again backlight gone. While in ON mode, touch the resistor leg of R9103 with multimeter on AC mode, the backlight comes back

[nomoresonys]

Re: Phillips TV no backlight

So did you test R9103 with your meter?

[DjKrish]

Re: Phillips TV no backlight

So did you test R9103 with your meter?

Yes, the reading is as above.

[nomoresonys]

Re: Phillips TV no backlight

Ok, my bad, I read it but it didn't register lol, must be something weak on that circuit maybe? what does it trace out to?