sound, no picture after varying periods, Vestel 17IPS20, 17MB100

[anyboby]

Hello Everyone!
First off, I am new in this forum and was very impressed, by how much information I was already able to draw from it, so a big thank you already!

I am currently trying to figure out a solution to a "sound, no picture" problem I am having with my Telefunken L48U300M4CW tv (48inch edge-lit LED TV) and I haven't been able to certainly determine the fault in the set based on my observations. Shortly after purchasing this tv it began turning off the screen after random, varying periods of times, while continuing the sound. A restart would always fix the problem, but I do feel like the periods of time, before the screen turns off are getting shorter. Movements of the LCD screen are still visible under Flashlight.

So I wen't ahead and did various measurements (based on the information I drew from this forum) in the set with my meter, so here are the main findings:
-all boards and hardware did look intact from a visual standpoint
-the out-voltage to the LED Panel of the PSU rises to 106Volts upon turning on the TV and rests on levels between 101 and 105 Volts. When the backlights of the tv are turned off randomly, the Voltage rises to about 117Volts instantly and drops down to 80, where it remains, while the LED background lighting remains turned off. (interestingly the LED-out-voltage is on a lower level around 97Volts when watching via netflix)
-I did measure the backlight on/off voltage on the PSU over the whole event and it remained on a constant 3.3 volts even when the backlights turned off
-I disassembled the TV to get to the LEDs of the edge-lit panel and checked every single one, they all worked when testing them in diode-mode

Now my current guess is, that it might be a main board problem, this is mainly based on MrReeceyburger123s comments (on this youtube video: https://www.youtube.com/watch?v=uPI1QBE0CxI&t=454s) where he says "Replace the mainboard if its turning off randomly".
Now I also have seen a video where the uploader found capacitors to be responsible for similar symptoms.

I'd be really thankful for any advice on how I should continue the troubleshooting to hopefully fixing this issue at some point!
anybobya

[vinceroger69]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

maybe try what reece suggests at 8.30 mins in this video measuring the vcc voltage and see if it drops out when back light fails

[dick_barton]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

While watching Netflix where you say the backlight voltage is set at a lower voltage 97V, does the backlight remain on longer?

[anyboby]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

Thanks for the quick responses!

While watching Netflix where you say the backlight voltage is set at a lower voltage 97V, does the backlight remain on longer?

In fact, my impression was, that when watching on Netflix, the periods where the backlight remains on are even shorter. The same goes for watching via HDMI. Also once the backlight has been shut down, the issue seems to accumulate and reoccurs in much higher frequency, making the set shut off the backlight shortly after restarting the tv.

maybe try what reece suggests at 8.30 mins in this video measuring the vcc voltage and see if it drops out when back light fails

I will definitely give this a try, just to make sure I got this right: If the mosfet vcc drops out when backlights are turned off, it is likely, that the LED-Controller-Chip is the culprit ?

[vinceroger69]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

yes thats how i understand it from the video solder a wire on too the vcc pin on the mosfet (google part number for vcc pinout) reconnect all boards turn on tv look at voltage when backlights on and when failed.just dont let that wire you soldered touch anything as you dont want too short psu out and cause more damage.

[CapLeaker]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

Turn the back lights waaaay down and see if they stay on longer. If that is the case there may be a failing LED.

[anyboby]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

Turn the back lights waaaay down and see if they stay on longer. If that is the case there may be a failing LED.

Hey, so I tested out this before getting to serious action on the psu and found this to be really working, the backlights stayed on cosiderably longer after turning down brightness and backlight from 50 to 0. That being said, is this already a clear indicator for the failure to be located along the LED strip?

I made a quick internet search for the model number of the display (VES480QNES-3D-U02) and discovered a replacement part on here: https://www.vareza-elektronik.de/pro...oducts_id=4829

I am not sure whether the stack repair as shown by MrReeceyBurger would work with an edge lit LED panel, especially when I haven't done anything like that before. Do you guys think the symptoms are decisive enough to purchase a replacement LED panel?

Edit: If it is the LED Panel, I assume it is a heat- or general overpowering-issue (since they work for a while before shutting down), so would there be any possibility to test the LEDs for this specific failure with a multimeter ?

[vinceroger69]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

did you try the test in post 2 i guess the driver ic could be failing under load?

[CapLeaker]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

Hey, so I tested out this before getting to serious action on the psu and found this to be really working, the backlights stayed on cosiderably longer after turning down brightness and backlight from 50 to 0. That being said, is this already a clear indicator for the failure to be located along the LED strip?

I made a quick internet search for the model number of the display (VES480QNES-3D-U02) and discovered a replacement part on here: https://www.vareza-elektronik.de/pro...oducts_id=4829

I am not sure whether the stack repair as shown by MrReeceyBurger would work with an edge lit LED panel, especially when I haven't done anything like that before. Do you guys think the symptoms are decisive enough to purchase a replacement LED panel?

Edit: If it is the LED Panel, I assume it is a heat- or general overpowering-issue (since they work for a while before shutting down), so would there be any possibility to test the LEDs for this specific failure with a multimeter ?

Well, I figured that is the case. LED's can fail like that and this turning down the back lights trick is a clear indicator to me that one or more back light LED's failing. Yes, best way is to replace the whole LED strip if you can. Reecey's trick works good too, but a new strip is the best. I've done all methods of repairing failed LED strips.
To answer your last question: No you can't do that with a DMM to find a failing LED like that. You have to power each LED or each LED strip up (I use a CV/CC variable lab power supply) and see which ones are failing.

Viel Spass bei der reperatur!

[vinceroger69]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

As these are edge strip leds you cant use the stacking method as far as i know? you maybe able to replace them though using a hot plate etc.

[anyboby]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

did you try the test in post 2 i guess the driver ic could be failing under load?

I didn't do that test, as I preferred trying the "non-invasive" test with turning down the backlights first. I think I will give replacing the LED-Panel a try, since the seller seems to offer return service and guarantees for functioning LEDs. If that won't solve it, I guess I will have to do further measurements involving some soldering!

Dankeschoen

[Andrew F. Ali]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

You got your answers.
1. Edge lit backlight LEDS cannot be repaired by the Stacking Method and cannot be properly tested with a DMM in Diode mode.
2. Though the individual beads can be replaced wit the Hot Plate procedure, replacing the entire strip is the BEST option, if you don't want to go in and repair them again.
3. Controller chip is a possible defect but I would rule that out for now as the voltages a good.
4. Finally. it is a LED Strip and NOT LED Panel as the Panel is the LCD screen glass and assembly.

[anyboby]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

4. Finally. it is a LED Strip and NOT LED Panel as the Panel is the LCD screen glass and assembly.

Ah, I got that mixed up, thanks for the hint

You got your answers.

yup, and I'm very happy with the support on this board!

[brianbelfast]

Re: sound, no picture after varying periods, Vestel 17IPS20, 17MB100

Hi. Seven months later I know, but just wanted to add a note. I just had a Panasonic TX55CX400B with the same symptoms. It would run happily for hours on Standard definition channels from it's own tuner. As soon as you try to display HD or 4K the backlight would go out. Restarting the set would bring it back on. Processor trouble I guess. BL on signal was disappearing. I tried a quick reflow just for fun but to no avail. Replacement 17MB100 did the trick.