JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

[tn245]

Got this TV. Owner said the screen went dim so he turned the backlight up to counteract which worked for a while but eventually it went almost black.

The LEDs are lighting up only just, three of them not at all on one strip. Have tested all the LEDs following ReeceyBurger's excellent video instructions and they all light up nicely. Voltage to the LED string from the PSU is only ~105V. I think this should be closer to 150V for 45 LEDs am I right? So I think this is a problem with the PSU. Just wondering if any of you have come across this before and can save me some time chasing down the problem.

Thanks!

[ReeceyBurger123]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

Hi mate, thanks for the feedback on the vid Your on the right path, the drive voltage is way too low. Possibly a shorted Led dragging down everything or maybe the drive amplifier is not turning on the mosfet enough. Silly question but what is the backlight setting at ?

[tn245]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

Hi ReeceyBurger. You're welcome. The videos are really helpful. As I said I tested all the LEDs and they all light up when tested in groups using the ATX psu method, which leads me to suspect the PSU. I did wonder what the backlight is set at but I'm not getting enough light output to see the screen at all so I haven't managed to check it. He said he'd turned it way up.

[ReeceyBurger123]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

Hmm yeah deffo something wrong with Psu then, normally if the Led booster mosfet or diode shorts then the Tv wont turn on at all. Sounds like the controll Ic for the mosfet has failed. It seems to be quite common on these Vestel Psu/Led drivers. I will put an ebay link to the Ic.

[ReeceyBurger123]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

Think this is the kit you will need:

http://www.ebay.co.uk/itm/VESTEL-17I...8AAOSwHPlWesfB

[ReeceyBurger123]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

I would say replacing the controller will likely fix the issue but you can replace the fet too if you want.

[budm]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

I see three of the LEDs are not on, are you sure they are not shorted out? If they are shorted out then the boost circuit will not be on, the 105V is the feeding Voltage to the booster circuit to raise it up higher by the booster. If those 3 LEDs are shorted out it will trip the over current protection circuit.
BTW, please also up load the pictures of the bottom side of the power supply-LED driver board.

[tn245]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

Budm, you're right those three don't light up under the TVs own power, but they do light up when powered up separately.

ReeceyBurger I will check out that controller thank you.

[budm]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

So if you leave the meter probes between the two legs of the booster output filter cap (47uF200V) laying on its side next to the LED connector then turn on the TV, do you see it jumps much higher than 105 VDC and then drops down to 105Vdc later on?

[tn245]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

So if you leave the meter probes between the two legs of the booster output filter cap (47uF200V) laying on its side next to the LED connector then turn on the TV, do you see it jumps much higher than 105 VDC and then drops down to 105Vdc later on?

123V and it stays there.

[vinceroger69]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

i would change the three leds which budm has pointed out maybe there on the verge of failing, in not sure if its worth changing that led strip for a diffrent location and see if the fault moves if it does it has to be that strip i guess.

[budm]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

123V and it stays there.

Please try it again but without the LED connector in place.
Also can we get the good clear pictures of the bottom side of the board?

The Diode (boosted Diode) on the top right of the board next to that small boost inductor L5201 tested OK?
https://www.badcaps.net/forum/attach...4&d=1458058395

[ReeceyBurger123]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

Well if he said they light with the meter probably means they are ok.... If one was shorted the meter will beep or show 0 ohms.

[ReeceyBurger123]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

Im currently doing the same panel now, I actually have 2 failed O/C Leds causing no Bl though. Will let you know what the drive voltage is when I fix mine.

[budm]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

I expect it to be around 150~160 range.

[Diah]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

123V and it stays there.

you need to test the Diode of the LEDS especially the off on, if the Diodes should read 785-750 any less than this average Bad Diode it lights but it limited the passing currents to the next one.

[ReeceyBurger123]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

Led drive voltage on 17ips20 for Ves400:

Backlight on Low: 162v Dc

Backlight on Med: 165v Dc

Backlight on High 169v Dc

[budm]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

I wonder if he is getting the BL-ON to start the booster circuit or not.

[ReeceyBurger123]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

Im quite sure he would be, these mainboards if the Blon was at fault im sure lock out and fail to give standby Led. Common fault is the Ic that drives the fet fails absolute crap Tv's Budm.

[tn245]

Re: JVC LT-40DJ51J - Vestel 17IPS20 - LEDs very dim

Thanks for all the suggestions guys. I'm going to have to wait until tomorrow to do the tests suggested. Will report back.