Just had one of these pop up - paid a bit more than I should but could see picture working as it was intermittent, so think it's lower risk.
Fault description: in use, after around 30 sec - 1 hour (essentially random) the backlight will switch off. Sound works ok during this. Nothing gets backlight to turn on again aside from a power cycle.
Power board & combined inverter part BN44-00264C (schematic here)
Found PFC cap voltage to be only 341V, which is too low. It is not boosting to the nom ~390V. I suspect that the set will intermittently cut out if the bus voltage sags below some limit (set by ICP802, KA431 zener-like device.) This might be latching or maybe the backlight does not restart after a UVLO event?
Anyway, I checked the Vcc voltage for the FAN7530 and it's ok, 14.8V. All PFC diodes ok. Source resistor ok. Haven't checked gate drive because I haven't got my isolation transformer set up. I suspect FAN7530 to be bad. Interestingly, I noticed the PFC voltage does rise slightly when the TV turns on - in standby it's 333V (~237Vac); when it fires up, it spikes to 343V (equiv ~244Vac) - I wonder if the inductor in the PFC circuit provides a little boost - or if the PFC circuit does actually work slightly but its regulation setpoint is too low...
Fault description: in use, after around 30 sec - 1 hour (essentially random) the backlight will switch off. Sound works ok during this. Nothing gets backlight to turn on again aside from a power cycle.
Power board & combined inverter part BN44-00264C (schematic here)
Found PFC cap voltage to be only 341V, which is too low. It is not boosting to the nom ~390V. I suspect that the set will intermittently cut out if the bus voltage sags below some limit (set by ICP802, KA431 zener-like device.) This might be latching or maybe the backlight does not restart after a UVLO event?
Anyway, I checked the Vcc voltage for the FAN7530 and it's ok, 14.8V. All PFC diodes ok. Source resistor ok. Haven't checked gate drive because I haven't got my isolation transformer set up. I suspect FAN7530 to be bad. Interestingly, I noticed the PFC voltage does rise slightly when the TV turns on - in standby it's 333V (~237Vac); when it fires up, it spikes to 343V (equiv ~244Vac) - I wonder if the inductor in the PFC circuit provides a little boost - or if the PFC circuit does actually work slightly but its regulation setpoint is too low...
Comment