Hitachi 48HBT62U K -Backlight problem

[Phil289]

Hi
Would be greatful for some help regarding this problem.

Tv turns on , Hitachi logo appears with no problems , then depending on how lucky i am i either get a fully working tv for around 5/10 seconds and then the left side of the screen dims down (not dark just dimmer than the right) or sometimes it will just go past the boot logo and go straight to the dimmed left hand side straight away.
Sometimes turning the tv off and then on again will make it fully bright again but it will then dim on the left shortly after.
It is a vestel setup with a 17ips71 (190814R4) psu board.

When the tv starts and the lights are fully working i get a low buzz from the psu board and when the lights dim down on the left the buzz goes,i'm not sure if this is relevant, the only other visable thing i can see is on the back of the psu board at Q17 is a component that has made a brown mark on the plastic backing sheet (maybe got hot?)

Any suggestions would be most welcomed
Thank you

[dskall]

Re: Hitachi 48HBT62U K -Backlight problem

What are your led voltages?

[Phil289]

Re: Hitachi 48HBT62U K -Backlight problem

If I measure at cn6 which is the led outlet at the 17ips71 i get the following -

When the backlight dims i get 186v on the black and 118v on the red
When the backlight is fully bright i get 186v on the black and 13v on the red

Thanks

[yokoono]

Re: Hitachi 48HBT62U K -Backlight problem

Backlight problems. Replace the LED strips.

[Phil289]

Re: Hitachi 48HBT62U K -Backlight problem

Sorry but couldn't see how to edit my previous post-

When the backlight dims(so only half the screen is bright) i get 86v on the black and 58v on the red
When the backlight is fully bright i get 86v on the black and 7v on the red (this will last for 5-10 seconds)

Also i'd like to ask-
If i remove the led connector from the psu board (cn6) should there not be a full amount of voltage at where the red wire connects as it only reads 4v?
On the cn6 connection i have a red wire,a black wire and a brown wire - what does the brown wire do ? - all 3 go inside the frame i presume to the led strips

thanks

[R_J]

Re: Hitachi 48HBT62U K -Backlight problem

On the cn6 connection i have a red wire,a black wire and a brown wire - what does the brown wire do ? - all 3 go inside the frame i presume to the led strips

thanks

Post pictures, How can we tell which pin the brown wire connects to? I suspect it is the return line for the second led string.
The power supply seems to be working ok, you have bad led's in the panel.

[Phil289]

Re: Hitachi 48HBT62U K -Backlight problem

Picture 1 is showing cn6 - the brown is the third pin from the left
picture 2 shows where it runs

Thanks

[R_J]

Re: Hitachi 48HBT62U K -Backlight problem

The black wire (pin1) is the led supply voltage to both strings (V_led+), the brown (pin3) is the return for one string (LED2_S), the red (pin7) is the return for the other string (LED4_S).
Check the voltage on the brown wire.

[Phil289]

Re: Hitachi 48HBT62U K -Backlight problem

The brown wire reads zero - dim or bright

Have attached some pics of how dim/bright it goes
Stayed bright for alot longer tonight - maybe because it was from cold ?

Thanks