Ok, had this one on the bench for a while. Toshiba 42" LCD, but that's not really important. Got it as a freebie, it's been on the back-burner for a bit.
Has the common LG-Philips 6632L-0450A/6632L-0451A inverter set on the LC420WX7 panel (720p 42")
Originally, slave had blown BD9897FS chip (a very common fault). Replaced chip & set fired up with backlight... but it had 2 secs to black fault. I checked the bulbs with the help of a friend, taking the whole panel apart. All bulbs lit up perfectly for those 2 seconds, and there weren't any signs of shorts/arcing on the bulbs or bulb ends.
Out of curiosity I bridged the timer capacitor on the master - no difference. I then did the same on the slave - the backlight stayed on. So, for some reason the slave is shutting down the backlight.
Using my scope I checked the master and slave waveforms, and there is a difference. The master has a duty cycle which ranges from about 0% to 20%. Whereas the slave varies from about 20% to 40%. It's almost as if the slave has a kind of DC-bias to it. So I decided to measure the 24V current. At 100% brightness, the current is more or less identical - 3.24A vs 3.85A - within margins of error for transformers, bulbs and PWM settings. However with the backlight brightness set to 0/100 (effectively 50%, the lower 50% being inaccessible to the user) the 24V currrents are 1.78A and 3.91A - the slave current does not reduce!
The other odd thing: The inverter seems to occasionally get stuck in a kind of "soft-start" mode, where it'll buzz slightly louder than normal although the backlight brightness is ok - it's something that happens when it first turns on normally, but it seems to also happen occasionally when it's running.
Has anyone seen anything like this? The slave board is cheap - but it feels like giving in to just replace it!
Has the common LG-Philips 6632L-0450A/6632L-0451A inverter set on the LC420WX7 panel (720p 42")
Originally, slave had blown BD9897FS chip (a very common fault). Replaced chip & set fired up with backlight... but it had 2 secs to black fault. I checked the bulbs with the help of a friend, taking the whole panel apart. All bulbs lit up perfectly for those 2 seconds, and there weren't any signs of shorts/arcing on the bulbs or bulb ends.
Out of curiosity I bridged the timer capacitor on the master - no difference. I then did the same on the slave - the backlight stayed on. So, for some reason the slave is shutting down the backlight.
Using my scope I checked the master and slave waveforms, and there is a difference. The master has a duty cycle which ranges from about 0% to 20%. Whereas the slave varies from about 20% to 40%. It's almost as if the slave has a kind of DC-bias to it. So I decided to measure the 24V current. At 100% brightness, the current is more or less identical - 3.24A vs 3.85A - within margins of error for transformers, bulbs and PWM settings. However with the backlight brightness set to 0/100 (effectively 50%, the lower 50% being inaccessible to the user) the 24V currrents are 1.78A and 3.91A - the slave current does not reduce!
The other odd thing: The inverter seems to occasionally get stuck in a kind of "soft-start" mode, where it'll buzz slightly louder than normal although the backlight brightness is ok - it's something that happens when it first turns on normally, but it seems to also happen occasionally when it's running.
Has anyone seen anything like this? The slave board is cheap - but it feels like giving in to just replace it!
