Vestel 17ips11

[CroTech]

So as the title says... I have got the most F-ed up power supply that I need to somehow repair since it is either impossible to get it in Croatia or too expensive.

First things first, it is a 32" Quadro LED LCD TV which all of a sudden did not wont to turn on, no backlight but there was some picture that could be seen in a dark room and the sound was OK.

Opened it up, tested the LED strips and there were 6 dead LEDs, replaced them put everything back up, nothing changed. Measured the output on the power supply and it gives 42 V on DC range and 96,4 V on AC that goes straight to zero after a few seconds.

I replaced the caps but that didn't fix the problem, and I dont know where to look since this the first LED that I am trying to repair.

Any suggestions?

The pics are here.

[Agent24]

Re: Vestel 17ips11

I recall there is a trick to bypassing LED strings with a zener diode of same voltage, to test if it's LEDs or PSU. Maybe some LEDs are still bad?

[dick_barton]

Re: Vestel 17ips11

With the leds disconnected what DC voltage do you have at the led output before it falls.
How many leds were in series?

[dick_barton]

Re: Vestel 17ips11

Looking at the capacitor close to connector CN101 rated at 100V I would expect the Led voltage to be somewhere near that voltage 70 - 80 V but this is just guess work.

[CroTech]

Re: Vestel 17ips11

The stripes are fine. I replaced the bad LEDs with new ones and tested it with 9v battery and 2 needles and every one of those shines bright light... The voltage without LEDs connected are the same and drop to zero. So it seems that fail protection turns on even though LEDs are not connected.

[dick_barton]

Re: Vestel 17ips11

Have you checked the Backlight On signal remains high at CN100 Pin 5

[Diah]

Re: Vestel 17ips11

The stripes are fine. I replaced the bad LEDs with new ones and tested it with 9v battery and 2 needles and every one of those shines bright light... The voltage without LEDs connected are the same and drop to zero. So it seems that fail protection turns on even though LEDs are not connected.

i dont know from where you got this way to test TV LED strips. this 2 needles you used reverse them with yours DMM and test the LED as diode way.. the one beep are bad. then one had Vf less than as usual are bad too. check and you will find you have one had diode shorted

[Agent24]

Re: Vestel 17ips11

i dont know from where you got this way to test TV LED strips. this 2 needles you used reverse them with yours DMM and test the LED as diode way.. the one beep are bad. then one had Vf less than as usual are bad too. check and you will find you have one had diode shorted

That's a good idea.

[CroTech]

Re: Vestel 17ips11

Have you checked the Backlight On signal remains high at CN100 Pin 5

Sorry I did not check but I will as soon as I get some free time...

Let me explain my "checking LED method" since it is simple, fast and bulletproof.

I take a 9V battery and solder a wire to a + and a wire to -
Now I solder + wire to a sewing needle, and - wire to a another sewing needle. Why sewing needle? Cause they are conductors and they can easily punctre the LED strip isolator. Now when the "TESTING DEVICE" is ready I take one end and try to pin the LED, once I see bright light from it I know that LED is good and if it is not shining any light I try to switch polarity and if that does not work, I take my hot air gun and solder a new one and then test it again, I can also test up to 3 LEDs in series but then they shine a little dimmer.

[dick_barton]

Re: Vestel 17ips11

But if you put 9V across a 3V led you have a very high chance of burning it out almost immediately, or if not you put the led under stress so that it fails sooner rather than later. Even if you do the same across a single 6V led.

Testing across 3 leds in series (3 x 3V = 9V) is the safer method.

[CroTech]

Re: Vestel 17ips11

I know, but having it stressed for half a second I dont think it damages it cause I have seen them shine even brighter through original power supply, that is actually how TV manufacturers make sure it fails after the warranty is out plus it is a old battery that is half way drained, that is why when you connect it to 3 LEDs in series they shine poorly.

As soon as I get my hands on TV again I will measure CN100 pin5

[Agent24]

Re: Vestel 17ips11

It's still bad practice. It's not terribly difficult to add even just one resistor.

[CroTech]

Re: Vestel 17ips11

Got the PCB to a frend of mine who repairs TVs and he told me that both of the SMD ICs on the back of the PCB (green side) seem to have wrong readings and that they should be replaced, so I am gone order new ones and ones I replace them I am going to make a new post.

Thanks guys

[ReeceyBurger123]

Re: Vestel 17ips11

Led driver Ic.

[CroTech]

Re: Vestel 17ips11

Led driver Ic.

ReeceyBurger, I presume you had the same problem? Cause I was reading about how dead LEDs and blinking LEDs can kill the power supply board.