Thomson 40M71NH20 Power issues

sa78fake on Sat May 21, 2011 4:30 am

Hi folks,

I've got an LCD TV which seems to have a power supply unit issue.

What happens is, that after I turn it on the standby LED goes on for a second and then turns off, if I unplug the TV the LED goes on for a sec again.
When I checked the secondary output voltages I had zero across the board (except the standalone 5V circuit which is independent of the main transformer).

I suspected the opto-isolators but they seem to be fine (and exchanging them didn't help either), also I checked the MOSFETs which power up the transformer but they have no voltage if I test them with the TV plugged in. So I suspected it's the PWM --> but FCC has voltage around 14 Volts, hence should be OK.

As you can see, I'm not getting anywhere - could anyone help with the symptomatic of the LED going on for a second after turning on the TV (and after turning off as well).

Many thanks!!