Working on a neighbor's LCD TV with LED back lighting. I don't have a service manual but have watched a lot of videos and read posts here. Looking for suggestions on how to proceed.
Back light (BL) may or may not turn on when TV is powered on. BL will sometimes remain on anywhere from a few minutes to up to 20 mins. BL may or may not return.
All testing is with BL set at mid level illumination
BL voltage is specified at 331V (per PCB silkscreen)
BL voltage with LEDs disconnected 395V
BL voltage with LEDs connected 260V
When BL goes off, BL voltage at Power Supply (PS) connector is 0V
BLU on/off = goes to 5V when TV is powered on and remains at 5V even when BL is off
PS on/off = 3.3V when TV is powered and is always present
PWM from main board is stable and always present even when BL turns off
To me it seems like the main board is fine. But why is the BL turning off? I suspect the PS but I'm wondering if the LED strings have an issue like drawing too much power causing the PS to shut them down? 260V loaded seems like quite a drop from the 331V spec but I'm not sure.
TV consumes about 20W when on with no BL
TV consumes about 25W with BL at min and 47W with BL at max
The PS says it can supply 289mA at 331V...which is 95W so that make me think that there's no issue with the LED string
I re-flowed many solder joints on the PS, measured some resistors values that I could get to and no bulging caps, nothing obviously wrong with it.
PS is a PD55AV1-CHS / BN44-00499A
Any test to further solidify where the issue lies? Thoughts?
Thanks!
Back light (BL) may or may not turn on when TV is powered on. BL will sometimes remain on anywhere from a few minutes to up to 20 mins. BL may or may not return.
All testing is with BL set at mid level illumination
BL voltage is specified at 331V (per PCB silkscreen)
BL voltage with LEDs disconnected 395V
BL voltage with LEDs connected 260V
When BL goes off, BL voltage at Power Supply (PS) connector is 0V
BLU on/off = goes to 5V when TV is powered on and remains at 5V even when BL is off
PS on/off = 3.3V when TV is powered and is always present
PWM from main board is stable and always present even when BL turns off
To me it seems like the main board is fine. But why is the BL turning off? I suspect the PS but I'm wondering if the LED strings have an issue like drawing too much power causing the PS to shut them down? 260V loaded seems like quite a drop from the 331V spec but I'm not sure.
TV consumes about 20W when on with no BL
TV consumes about 25W with BL at min and 47W with BL at max
The PS says it can supply 289mA at 331V...which is 95W so that make me think that there's no issue with the LED string
I re-flowed many solder joints on the PS, measured some resistors values that I could get to and no bulging caps, nothing obviously wrong with it.
PS is a PD55AV1-CHS / BN44-00499A
Any test to further solidify where the issue lies? Thoughts?
Thanks!
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