Vistel 17IPS19-4 V1 Backlight Flashing On & Off

[dididave]

Hi There,
Looking for a bit of help with a Polaroid 32" LCD TV which uses the Vistel 17IPS19-4 PSU Board.

Fault :- Tv switches on out of standby and the lcd backlights power up and then power down and keep doing this untilll i switch the set back to stand by.
You can hear the PSU under pressure while its doing this.

I bought two of these sets from the same person who had bought them at the same time and both failed 14 months later two weeks apart.

The first of them i have repaired using some of the parts from this set.
I have now replaced these parts with new.

D320,D319,D318
D206,D207
D506
Mosfet and LCD Driver chip on the under side were also replaced as used on the other set.

Having replaced these I now have the set back to what it was doing first off

The set just keeps powering up the back light and off again - In the end i left it doing this in the hope something would show up.

After about 20mins C514 gave a puff of smoke and failed.

This however is not the faulty part as i replaced it and still have the same problem.



Any suggestions would be great.

Thanks

[ReeceyBurger123]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

Have you checked the Smd diodes in the Led drive circuit ? They also can fail. Also is there a short across that cap that keeps blowing ?

[dididave]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

PSU Board and Main Board swapped out with other working unit and still same issue .
Pulsing whistling sound and screen back lights light up and off thrn on again ?

[ReeceyBurger123]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

Hmm maybe there is a lose connection between the Led strings and the branch Pcb, I can link my video on how to test this if you want ?

[CoolJc]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

Hi DidiDave - Did you resolve the blinking LED backlight problem? I have a JVC LT-40DG52J with same PS doing exactly as you described

[CoolJc]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

Any info from anyone grateful received -
JVC LT-40DG52J with a PS 17IPS19-4 - LED driver IC TPS61199 - backlights rapid 'blinking'

I understand a HITACHI 40HXC06U has same arrangement

Imagined it must be a PS fault - bought S/H replacement from Ebay but no cure, chances of finding a panel with exact same fault seems low?

Removed screen to check LED bar - LG INNOTEK 40INCH 7020PKG 54EA edge illuminated arrangement - 2x strips of 54 leds across the bottom edge, each strip has 2x sets of 27 leds, all 4 sets test identical with LED tester, all leds light up,

By chance I had 4x set side edge from a Toshiba, shorter run but same connector, thought it worth a try - blinks just the same

Can't see the fault is coming from the main board?

Going round in a circle with this one

Seems LED voltage keeps stepping up till OVP kicks in - but that would mean the replacement PS has same fault or instruction from main board ???

[nomoresonys]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

Can you post some good focused straight on pictures? one of the whole back and of each board.

[CoolJc]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off



Have now replaced control chip but no cure - all 4x led strings test the same voltage and current draw on LED tester - Seems a common problem with this PS across a range of models - strange can't find answer

[nomoresonys]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

didnt understand, what is the "control chip"?

[dskall]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

What is your led voltage going up to?

[CoolJc]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

Control chip - LED driver IC TPS61199

Yes, I'm wondering if the 'blinking' is being caused by 'over volt protection', that would fit with the 'blinking' only happening on low led setting, and stops on 'dynamic' picture setting

LED supply voltage reads around 77v with multimeter - which ties in with the reading from the LED meter, and each string is 27 leds @ ~3v = ~81v

But I replaced the PS, so - both PS's faulty?
Or
All 4x LED strip faulty? - consisting of 27 led's each string - ware & tear - each not drawing sufficient current - allowing supply voltage to climb too high?

Anyone know how the LED voltage is controlled - can it be adjusted down or limited?

[vinceroger69]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

does your led tester show how many mah are being used on each strip

[CoolJc]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

There are 2x leds strips each with 54 leds - each strip has 2x separate strings of 27 leds

Today's update -
I now firmly believe it's a fault with LED's - yet I can see what
Why? I was using the scope to compare each of the 4x strings returning to the driver IC TPS61199, on connecting to one of the 4x strings the blinking stopped! didn't stop if I used the multimeter, seems the scope presented a different load? so I swapped that return with one of the others, sure enough the effect moved, the blinking also stops if I connect a 100k resistor to 0v, but not if I connect 1m ohm

So, I can stop the blinking with a 100k resistor from one of the 4x string to ground - next to no load, but it works - but here's the weird thing - the PS is noisy, it's not happy (as described in an earlier post)

Now, the circuit diagram I have for a 17IPS19-4 shows a 33v zener connected to 0v on to each of the 4x string returns - but there are none no my board - I will try tomorrow - but I'm now convinced it must be a fault with that 1x string

[nomoresonys]

Re: Vistel 17IPS19-4 V1 Backlight Flashing On & Off

I think so too, can you check each led on that one individually? a faulty one might be dimmer than the others or something.