Telefunken TLEDD-32HDR no back light

[Grunder]

Hi Guys,

Just when I thought I was on top of this issue, I get pitched a curved ball!

Telefunken TLEDD-32HDR with no back lights.

Photo1
The set has three led strips connected in parallel with a supply of 25 volts.

Photo2
I have measured the 25 volts at the beginning of each strip. I double checked using my 'scope and the 25 volts is ripple free. No voltage present on ANY of the leds on ANY of the strips.

Photo3
There are test points between each individual led, but strangely don't measure continuity, and the leds wont illuminate using the meters diode setting as it did on a similar set.

The 25 volts is supplied by diode DB801 & smoothed by caps EB801 & EB802 47uf/100v in parallel.

please help.

[dick_barton]

Re: Telefunken TLEDD-32HDR no back light

You should be able to find where the open circuit is using your meter on continuity.
There have been mention of the led strip connectors being of poor quality so you may have a problem at the connection to the strip.

[Grunder]

Re: Telefunken TLEDD-32HDR no back light

You should be able to find where the open circuit is using your meter on continuity.
There have been mention of the led strip connectors being of poor quality so you may have a problem at the connection to the strip.

Thanks man will double check, even though the leds are mounted on quite a thick aluminium looking Strip. (photo)

After another think about it, maybe the supply voltage could be too low. The set comes on with a dull red standby led then goes brighter. I assumed (yes, I know) that the brighter led indicted that the set is switched on, however now I see that the STANDBY led has three legs, indicating that there must be a green ON led.

This makes me think that the set isn't coming out of standby, and that the 24volts to the leds is insufficient. My initial thoughts.There is a regulator on the main board with 3v3 on one of the legs, so guessing the processor has stopped working. Have priced a main board in S.A. but not available new, only second hand with no guarantee. Dont think I will buy off the net, to dicey. Will have a last poke at it, and post if I find a solution. Zero Bravo, right out.

[ReeceyBurger123]

Re: Telefunken TLEDD-32HDR no back light

Have you tested all the Leds ?

[dick_barton]

Re: Telefunken TLEDD-32HDR no back light

I would agree that 24V does not seem right. I suspect you may well have a power supply fault. Can you measure all the voltages alongside the connector with the legends alongside. EG 12V, 3.3V, P_On, 5V etc. and tell us what you find.

[ReeceyBurger123]

Re: Telefunken TLEDD-32HDR no back light

Sorry your post above mine didn't come though, yes 24v is not correct. The leds in series meaning they need about 70v to drive them all. The 24v means the booster is not being turned on. Being on of them cheap boards I would say you have corrupt firmware the voltage reg is probably ok but not receiving the proper drive voltage for it.

[ReeceyBurger123]

Re: Telefunken TLEDD-32HDR no back light

Now if you got 70v at start up then it went down to 24v that means you have a bad Led shutting down the driver.

[Grunder]

Re: Telefunken TLEDD-32HDR no back light

Now if you got 70v at start up then it went down to 24v that means you have a bad Led shutting down the driver.

Thanks, been busy rechecking in the mean time, I must check that voltage on switch on to see if it drops.

on re-checking what i thought were test points weren't at all. So I popped off all the "lenses" on one strip and prepared three leds for some tests Photo's 1&2

This included my old faithful 12 volt supply, jumper leads, dmm, & a 2.2 kilo ohm & a 1.8 meg ohm resistor photo3

With my meter connected in series with one led, and using the 2k2 as a limiter resistor the led illuminated quite brightly, showing a draw of 3.4 milli amps photo 4

substituting the 2k2 limiter resistor with 1.8 meg resistor the led illuminated very dimly with a current draw of 3.8 micro amps (if my meter is to be believed, its a cheapie) photo 5

2 leds in series with the 2k2 resistor showed a draw of 1.1 milliamps with fair illumination photo 6

2 leds in series with no limiter resistor shows very bright illumination photo 7
(no amps were measured as my meters 10amp facility is bust, sorry)

3 leds in series with no limiter resistor shows no illumination. photo 8

Sorry if this seems tedious, but i was trying to determine the voltage & amperage necessary to illuminate one Strip of leds versus one led.

I'm still at a bit of a loss as to the minimum and maximum voltages required for a full strip illuminated, but will try to get the voltage up to +/- 70 volts as you suggest. Thanks all, like Arnie said " I will be back".

[dick_barton]

Re: Telefunken TLEDD-32HDR no back light

With my meter connected in series with one led, and using the 2k2 as a limiter resistor the led illuminated quite brightly, showing a draw of 3.4 milli amps photo 4

12V supply, 2K2 ohms and 3.4mA
Volts drop across resistor = 7.48V so leds have appox 4.5V drop.
The 1M8 Ohm is far to high a resistor for the leds to draw any current as you noticed.

So you can now calculate approximately what voltage is required to drive the string of leds.

[budm]

Re: Telefunken TLEDD-32HDR no back light

Vf of the ONE White LED should not be that high.
Are you sure your regulate power supply is putting out 12V?
You should Check the Vdrops on the LED.

[budm]

Re: Telefunken TLEDD-32HDR no back light

How many LED per strip?
Can we see the pictures of the bottom side of the board where the LED connector is?
Pictures of the WHOLE backside of the TV?
I doubt that the LEDs strips are connected in parallel.

[dick_barton]

Re: Telefunken TLEDD-32HDR no back light

The led looked very bright for 3.4mA. Would that be right?

[budm]

Re: Telefunken TLEDD-32HDR no back light

The led looked very bright for 3.4mA. Would that be right?

No, unless the camera is being fooled.

[dick_barton]

Re: Telefunken TLEDD-32HDR no back light

My thoughts also.

[Grunder]

Re: Telefunken TLEDD-32HDR no back light

12V supply, 2K2 ohms and 3.4mA
Volts drop across resistor = 7.48V so leds have appox 4.5V drop.
The 1M8 Ohm is far to high a resistor for the leds to draw any current as you noticed.

So you can now calculate approximately what voltage is required to drive the string of leds.

Thanks Dick, yes 6x4.5 = 27volts, and then they would just be illuminated. I erred in saying "quite bright". they were just "turned on". With the 1.8 meg the led turned light grey from the dark grey (threshold?)

[ReeceyBurger123]

Re: Telefunken TLEDD-32HDR no back light

Your making this way too complicated than it needs to be. Each led needs about 3v, so count how many are on the strip then figure out what is needed for one strip. Normally about 27v for one so that's 3 9v batteries to test one strip.

[Grunder]

Re: Telefunken TLEDD-32HDR no back light

Vf of the ONE White LED should not be that high.
Are you sure your regulate power supply is putting out 12V?
You should Check the Vdrops on the LED.

Thanks budm, not familiar with term Vf. The output of the dc supply was 12.5 volts. The way i saw it was +/- 2volts across the 2k2, and 10v/2 making 5v across either led. Making them turn on?

Three leds & no limiter 12v/3 = 4v per led, not enough to turn the leds on?

[ReeceyBurger123]

Re: Telefunken TLEDD-32HDR no back light

Thanks budm, not familiar with term Vf. The output of the dc supply was 12.5 volts. The way i saw it was +/- 2volts across the 2k2, and 10v/2 making 5v across either led. Making them turn on?

Three leds & no limiter 12v/3 = 4v per led, not enough to turn the leds on?

If the Leds don't turn on if you apply that voltage one is O/C and failed normally unless they are all like that ? If so you have not wired them properly.

[Grunder]

Re: Telefunken TLEDD-32HDR no back light

Your making this way too complicated than it needs to be. Each led needs about 3v, so count how many are on the strip then figure out what is needed for one strip. Normally about 27v for one so that's 3 9v batteries to test one strip.

I agree, I had to satisfy my curiousity, my mistake was not to pull the plug on the leds and see the 24 volts didnt change. the problem lies with the main board, its not available new, the customer is not interested in a second hand pcb so the set is returned unrepaired.

Will try a less complicated angle of attack on the next one. Most appreciated for your guys responses.

[ReeceyBurger123]

Re: Telefunken TLEDD-32HDR no back light

Ok no worries worth a shot ehy