Changhong TV backlight turns off (bad lamp or bad inverter ?)

[Dannyx]

Good evening to all of the wonderful folks here. Time for another entry into the "chinese stuff that refuses to be fixed" category. This TV has a faulty backlight, similar to the "2 seconds to off" business, except it's even shorter than that: around 200ms or so after the inverter tries to turn on. When facing CCFL backlight issues I usually address them in two ways: check the inverter, then check the lamps. If one fails, the cause is obviously the other one. In this case, (aside from a bulging cap that I replaced) I removed the HV transformer and measured the resistance of the primary and secondaries respectively: they all had nearly identical values, that is, almost short circuit for the primaries and around 500 ohms for the secondaries. Although it is still theoretically possible for those secondaries to have failed, I find it highly unlikely they broke down at the same time and reached the exact same resistance. Then I soldered the transformer back in place, I took two CCFLs I had laying around and soldered them to the two HV terminals: same issue - the TV tries to turn on, but turns off very shortly after. Again, it could be that these lamps are on their way out too, since I don't know their history, but there's no way I can check them, is it ? The biggest issue is that apparently the whole goddamn internet never heard of this power supply (no joke: google told me no results were found when I searched the exact model). It's a Megmeet MP236CMC....I gotta admit, that name itself makes me wanna punch something :| I then though I'd pull of the trick of disabling the controller ICs timeout circuit to force the lamps on regardless of their condition. I flipped the board over and located the control IC, however, same issue as before: could not find any helpful info on this sucker. Apparently someone decided to design a TV with the most obscure parts on the planet.....and succeeded. It's an OB3306QP and THIS is all I could find on it.....end of story. With all my (basic ?) knowledge of monitors and displays, I was able to follow that example application in the "datasheet" and compare it to my board, as well as with ANOTHER similar IC, the OB3309 and I kinda figured out what those pins do to a degree, however the 09 model has an actual PROT pin, which is exactly what I was looking for in order to disable the protection, except my IC doesn't have that, so what the hell do I do here ? :| It seems to me that those CS pins are the ones triggering the shutdown - I tried grounding them via a 1 ohm resistor, but that only caused the backlight to stay on for slightly longer before going out again... What it seems to me is that the voltage on those CS pins can't be neither too high (which would be a shorted lamp), neither too low (would be an open lamp) - it has to be in a "ballpark" with respect to a reference which I can't figure out how is set Perhaps those more professional than me could have a look and give me a clue. Cheers.

[Dannyx]

Re: Changhong TV backlight turns off (bad lamp or bad inverter ?)

UPDATE: I decided to carefully read the information given in the datasheet for the 09 model which is actually complete and I might actually have to pull the CS pin HIGH to VDD instead of LOW to GND like I initially though, because it says there the IC shuts off if the CS voltage is less than 0.8v, so by pulling it to ground we're doing just that...