Grundig 48 VLE 5429 BP TV no backlight

[Kassu]

Hi,

Got an old TV from a friend. Works fine otherwise, turns on and the picture is there, except that the backlight doesn't turn on, not even for a second. Checked the output for the LEDs and got zero volts, so I would think the lights are fine but just not getting power. So, any idea where the problem might be?

The power board is Delta DPS-120AP-2 and main board TC-4 GDTC E131175 if that helps. Pics included.

There's an FQPF16N25C MOSFET there besides the LED connector. Is it used to dim the backlight and could it be the problem? Or that the mainboard doesn't tell the power supply to turn the lights on? There's a BL_ON/OFF pin which seems to be for that.

Also, I found this video where this guy wires the output straight to the transformer. Not the exact same model as mine but seems to be close. Doesn't seem like a very good idea to me. What do you think? Even if it works wouldn't it disable any backlight brightness adjustment?
https://www.youtube.com/watch?v=_J9wRNtYuq0

Thank you!

[budm]

Re: Grundig 48 VLE 5429 BP TV no backlight

https://www.badcaps.net/forum/attach...0&d=1513877909
What do you get on the BL-ON pin when the TV is OFF and when the TV is ON?
What DC Voltages do you get between the two legs of C700, C720 when the TV is first turn on? You will have p leave the probes in place when you turn on the TV.
We also need the straight shot pictures of the whole top and bottom side of this Power supply/LED driver board.

[Kassu]

Re: Grundig 48 VLE 5429 BP TV no backlight

https://www.badcaps.net/forum/attach...0&d=1513877909
What do you get on the BL-ON pin when the TV is OFF and when the TV is ON?
What DC Voltages do you get between the two legs of C700, C720 when the TV is first turn on? You will have p leave the probes in place when you turn on the TV.
We also need the straight shot pictures of the whole top and bottom side of this Power supply/LED driver board.

BL_ON - tv off 0v
BL_ON - tv on 2.56v Should be 3.3v?

Do you mean I would have to instantly measure the caps after I turn on the TV because these are taken about a minute later?
C700 155v
C720 154.6v
Markings on the PCB say LED driver output for the 48" model is 186V. 155V seems quite a bit lower than that.

Included more pics with and without flash from both sides.

[William1967]

Re: Grundig 48 VLE 5429 BP TV no backlight

The solution is simple, these displays are known for the defective led stips. Check the display inside and you find in most cases more than one led / led strip defective.

[budm]

Re: Grundig 48 VLE 5429 BP TV no backlight

"Do you mean I would have to instantly measure the caps after I turn on the TV because these are taken about a minute later?
C700 155v
C720 154.6v"

You will have to leave the meter probes on the two legs of the cap, using clips or what you have, then turn the TV on to see how high the Voltage goes up to before it setlles down to 155V.

[thoma]

Re: Grundig 48 VLE 5429 BP TV no backlight

http://forum.iwenzo.de/grundig-servi...e--t61847.html

http://forum.iwenzo.de/grundig-tv-so...leme--f45.html

[Kassu]

Re: Grundig 48 VLE 5429 BP TV no backlight

The solution is simple, these displays are known for the defective led stips. Check the display inside and you find in most cases more than one led / led strip defective.

You might be right. I'll check them next. I measured the LED output again when turning the TV on and it jumps to about 100v for a split second. If there's a broken LED will the power supply turn the LED output off because of not being able to supply current?

"Do you mean I would have to instantly measure the caps after I turn on the TV because these are taken about a minute later?
C700 155v
C720 154.6v"

You will have to leave the meter probes on the two legs of the cap, using clips or what you have, then turn the TV on to see how high the Voltage goes up to before it setlles down to 155V.

Alright. Got the same 155v on C700, but about 234v on C720 for a second.

[budm]

Re: Grundig 48 VLE 5429 BP TV no backlight

You might be right. I'll check them next. I measured the LED output again when turning the TV on and it jumps to about 100v for a split second. If there's a broken LED will the power supply turn the LED output off because of not being able to supply current?



Alright. Got the same 155v on C700, but about 234v on C720 for a second.

That is the key! you open circuit in the LED connection some where, more likely open LED/s, that is why the Voltage jumps up that high due to no load so the protection circuit kicks in and drops the Voltage back down.

[Kassu]

Re: Grundig 48 VLE 5429 BP TV no backlight

Great! Found the broken LEDs. I'll order new ones. Thank you all for the help!

[jornet2001]

Re: Grundig 48 VLE 5429 BP TV no backlight

Great! Found the broken LEDs. I'll order new ones. Thank you all for the help!

Hi, I have a Grundig tv 48 VLE 6420 with the same problems as yours. I wanted to know if changing the LED strips fixed everything. Thank you.