Phihips 47pfl5704d / f7 Back light not working

[cwolford]

Phihips 47pfl5704d / f7 Back light not working

When it turns on it has a low glow on right and left side of the screen. Like the lights are trying to come on. Then it goes black.

With a flash light I can see menu, av, etc.

With the back off, you press power button a green led come on near the cpu.

It stays on if I leave tv on.

No signs of bad caps, busted / cracked IC, or missing IC legs

There is one resistor that looks suspect , although I cannot read its value as it 5th band is black.

I think the psu has the backlight inverter built in.

The photos posted are top and bottom of the PSU.

This old post I found https://www.badcaps.net/forum/showth...=47pfl5704d+f7

About me:
Have Computer repair knowledge, car repair knowledge, some electrical engineering knowledge not a lot not in school atm. Only have access to my tools.

Please assume I don't know how to test a part, it has been a while since a played with IC.

I know resistors have to be out of circuit to test.
I know ac / dc
I know ohms / amps / volts / ground / continuity
I have replaced SMD by hand it's a pain.coun
I have replaced through the hole components
Don't remember how to test diodes / caps / relays.
Don't remember what how to test or how they function MOV/mosfet
Forgot stuff about using dmm oL vs o.oo ect. I will need a quick brush up, if i cant remember i will ask.

Tools:
All kinds of hand tools
Hakko soldering station fx-888 + other soldering tools
DMM : uni-t UT61E
analogue multimeter
Sparkfun arduino invetor kit
Old PC PSU willing to use for benchtop psu

[cwolford]

Re: Phihips 47pfl5704d / f7 Back light not working

Bottom photos and one more of the top.


I can take more photos of what ever area if they are not clear enough. Will work on getting better photos anyway.

I can put back in to do volt test too. Looking for what to do now, also maybe guide me through why you think i need to test xyz. I want to learn as i go thanks.

[dskall]

Re: Phihips 47pfl5704d / f7 Back light not working

You might want to look at this post https://www.badcaps.net/forum/showth...er+testing+cfl

[cwolford]

Re: Phihips 47pfl5704d / f7 Back light not working

This would tell me if it was bad psu or back light right? I assume that the back lights connectors are the 2 (2 wire ) connectors that run to the LCD pannle from the PSU.

The connector on the PSU have 3 pin But the Connectors only use 2. See photo.


EDIT
TO any one: The resistor with the spot on it, that might be bad, that i dont know how to read. Its is located between heat sink 2 and 3. I labeled them at some point.

[dick_barton]

Re: Phihips 47pfl5704d / f7 Back light not working

The resistor with the spot on it, that might be bad, that i dont know how to read. Its is located between heat sink 2 and 3. I labeled them at some point.

Try and take a clear photo of it showing its colours and also what you meter reads when you measure it.

[dick_barton]

Re: Phihips 47pfl5704d / f7 Back light not working

What DC voltages do you have on DIM & BL_ON/OFF (pic5, Post #2) when you power up out of standby.

[cwolford]

Re: Phihips 47pfl5704d / f7 Back light not working

Try and take a clear photo of it showing its colours and also what you meter reads when you measure it.

5 band resistor brown blue blue gold black

I will remove it after i use the dmm on the psu to get the volts you want. Then I will use the DMM on it.

I posted a better photo of it in the first post, i Added the one on the 2nd as it shows the spot better.

https://www.badcaps.net/forum/attach...9&d=1488508394

[cwolford]

Re: Phihips 47pfl5704d / f7 Back light not working

What DC voltages do you have on DIM & BL_ON/OFF (pic5, Post #2) when you power up out of standby.

Dim volt readings:
power on ~3.3v then jumps to ~14v Then settles at ~1.68v

BL_ON/OFF power on:
it spikes some times But always settles at ~3.17v
Power on 3 times. The spike is like less than second.
1st time ~5v
2nd time no spike just ~3v
3rd time ~10v

So if i ground Bl_ON/Off The side of the tv light up but dont kick on. IT was an accident

[CapLeaker]

Re: Phihips 47pfl5704d / f7 Back light not working

If you get BLon at 10V DC, there is something totally wrong, because you only have 5V STBY. So either there is a measurement error or your batteries in your DMM are low.

The BLon comes from the main board. Shorting that to ground is not good at all. That's another way of kissing the main board good bye.

[cwolford]

Re: Phihips 47pfl5704d / f7 Back light not working

If you get BLon at 10V DC, there is something totally wrong, because you only have 5V STBY. So either there is a measurement error or your batteries in your DMM are low.

The BLon comes from the main board. Shorting that to ground is not good at all. That's another way of kissing the main board good bye.

If you look at the board, my probe slipped off and hit the ground right next to it.

I tested it like 5 or 6 times and It only hit that high number once.

it was for a split sec as soon as it powered on, I wish i could log it with a better dmm, but it may be just my dmm not able to take reading fast enough.

[cwolford]

Re: Phihips 47pfl5704d / f7 Back light not working

the resistor i don't know the value of measured 0.29 ohms
5 band resistor brown blue blue gold black
or red grey grey gold black

The two in the middle look shine not sure if blue are grey. Too the eye they look the same color. In photo they look different.

the first one could be red or brown not sure.

I dont know what to do about the black at the end tho.

[budm]

Re: Phihips 47pfl5704d / f7 Back light not working

You reading the resistance of the meter leads + the resistance of the resistor, it looks like 0.18 Ohms resistor, so it is OK.

[budm]

Re: Phihips 47pfl5704d / f7 Back light not working

the resistor i don't know the value of measured 0.29 ohms
5 band resistor brown blue blue gold black
or red grey grey gold black

The two in the middle look shine not sure if blue are grey. Too the eye they look the same color. In photo they look different.

the first one could be red or brown not sure.

I dont know what to do about the black at the end tho.

That R517 is the Source resistor for the power MOSFET Q501 which drives the power transformer T501 for the 12V and +VAMP power supply. So if you do have +12VDC at the connector then that power supply section is working.

This looks like your power supply:
Philips 272217100692 Power Supply / Backlight Inverter
http://www.shopjimmy.com/catalogsear.../?q=47pfl5704d

Pictures provided by shopjimmy.
So if you look at the TV in the dark, do you see the backlights even flash on for seconds?

[cwolford]

Re: Phihips 47pfl5704d / f7 Back light not working

Yes there is an 4 inch glow up and down the left and right side.

[budm]

Re: Phihips 47pfl5704d / f7 Back light not working

Are you getting about 380~400 VDC between the two legs of either one of the two 450vdc main filter caps laying on its side when TV is turned on?
It sounds like the inverter is running but not putting out enough high Voltage to light up the whole length of the lamps., it may be inverter transformer too.
Is there any sign of over heated inverter transformer T701? Look real close on top and bottom side of the board where the inverter transformer is.

[cwolford]

Re: Phihips 47pfl5704d / f7 Back light not working

I want to make damn sure I do this right. That's high voltage. Am I probing ground and a leg of the cap or using both legs. And ground as in metal frame.

[cwolford]

Re: Phihips 47pfl5704d / f7 Back light not working

Between the legs of each cap its 398 to 400v

I don't know what to look for in the transformer but it does not look melted or discolored.

[cwolford]

Re: Phihips 47pfl5704d / f7 Back light not working

"it does use CCFL and it has circuit board inside the panel with Balancer cap for each tube," should I tear it down and look a the balancer caps?

[cwolford]

Re: Phihips 47pfl5704d / f7 Back light not working

I would like to check the inverter transformer, but not sure I can if these are the right specs it is to give out:
Min. Type. Max
VBL 1150 1350 1550 VRMS

I don't think my dmm can read that it's to high. Any input?

[CapLeaker]

Re: Phihips 47pfl5704d / f7 Back light not working

You could measure that with a high voltage probe no problem. But not everyone has this. Could be a bad transformer, bad caps, cold solder joint etc.