Dear everyone,
I am asking for help to repair this board, as I were not able to solve it on my own.
Symptom: it has 5V standby, but if I connect the PS-ON pin to high level, the PFC tries to start for a brief moment, but the highest it goes is around 360VDC. If I put it back into the TV and start it with the mainboard, this brief moment extends to about 0.7 second. But it makes the same issue. In the past, the tv was working, altough the voltage on the main filter cap seemed low (around 380V, datasheet suggests 395V)
So far I have done this:
Check all diodes
Check all resistors
Recap the whole board with quality caps
Changed the 3 smps ICs: IC901, IC902, IC905
IC905 makes the 5V standby, as I said, it worked before, but I decided to change it also.
Changed Q902 PFC FET to a new one
Nothing helped from the above list. What I noticed, the VDD-S line is 5.8VDC in standby, and it goes higher to about 12-13VDC when I try to start the board, but only for a fraction of a second, then it falls back to 5.8V. I was only able to see it via scope. This 5.8V on the hot side is produced by PIN2 of IC905. From here on, I am clueless. Please see the attached SM, it is on page 44 (power 42" & 47"). There are components marked _NC, they are for the 47" version, are left out on my board.
Thank you
I am asking for help to repair this board, as I were not able to solve it on my own.
Symptom: it has 5V standby, but if I connect the PS-ON pin to high level, the PFC tries to start for a brief moment, but the highest it goes is around 360VDC. If I put it back into the TV and start it with the mainboard, this brief moment extends to about 0.7 second. But it makes the same issue. In the past, the tv was working, altough the voltage on the main filter cap seemed low (around 380V, datasheet suggests 395V)
So far I have done this:
Check all diodes
Check all resistors
Recap the whole board with quality caps
Changed the 3 smps ICs: IC901, IC902, IC905
IC905 makes the 5V standby, as I said, it worked before, but I decided to change it also.
Changed Q902 PFC FET to a new one
Nothing helped from the above list. What I noticed, the VDD-S line is 5.8VDC in standby, and it goes higher to about 12-13VDC when I try to start the board, but only for a fraction of a second, then it falls back to 5.8V. I was only able to see it via scope. This 5.8V on the hot side is produced by PIN2 of IC905. From here on, I am clueless. Please see the attached SM, it is on page 44 (power 42" & 47"). There are components marked _NC, they are for the 47" version, are left out on my board.
Thank you
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