Sansui 55" LCD TV Model STY955 Backlight or PSU???

[angelos]

Hi Guys,
This tv came in with a back light that used to switch off intermittently. After measuring around the PWM IC and i can confirm that i made NO SHORT CIRCUIT the LED's went quite dark and stayed like that. They barely shine!!!
This is the readings i have,
LED+ = 38.6V
LED+ = 38.6V
LED+= 38.6V
LED+= 38.6V
LED+= 38.6V
LED+= 38.6V
LED6- = 1.62V
LED5- = 1.60V
LED4- = 1.61V
LED3- = 1.62V
LED2- = 1.62V
LED1- = 1.63V

also the Adjust pin is 5.1V
and BL-ON = 1.6V

If i use a backlight tester and they all come on, not to say that they are not intermittent but the LED tester indicates a voltage of 41V on all six circuits and there is a blueish light emanating from the rear stand offs. I guess being biased slightly.
Previously before these back lights went from intermittent off to permanently dim i did take off the LCD display and put power to see that all LED's came on nice n bright and then after a few minutes they just faded off. I then started fault finding around the PWM and that's what caused the failure of output voltage.
Just to give you an idea i disconnected one of the LED- leads and put my Fluke meter in series to monitor the current and when i powered up the TV the backlights flashed and went off immediately. As if it did not like the fluke in series and i cant understand why.

My question is, is it the back lights or the power supply?

[budm]

Re: Sansui 55" LCD TV Model STY955 Backlight or PSU???

1) TV OFF, put meter probe on the the two legs of capxon cap C13 (100uf 100V).
2) Set meter to 200V scale then turn on the TV while watching the meter to see how high it goes up to then wait 10 seconds to see how low it goes down to.
3) Report the reading.