LN55C650L1FXZA Backlight Woes

[toddw65]

Hi All,

I have a Samsung LN55C650L1FXZA with the BN44-00342B PS/Inverter with backlight troubles. It was working intermittently and once on, would stay on, but then once it was warm and was shut off the backlights wouldn't come back on when the set was restarted.
Now all it will do is flash for a couple of seconds and then there's a picture/sound but no backlights. Every so often I can power it up with the main board disconnected from the power board and the back lights will stay on, but not every time.

With the set powered up I get:

18.8v on all of the 13/18 pins
12.9v on all 13v pins
5.6v on all the 5v pins
Lamp_Det is zero volts
Sw_Inv: 5.09v
Pow_Sw: less than 1v
And on the large caps I'm only getting 162v

I didn't see any obviously bad parts and I pulled and checked ci818 because I've seen that mentioned as a common failure and it tested fine. I also pulled and checked several electrolytic caps even though they looked fine, but all tested ok.

Thanks in advance for any assistance.

[nomoresonys]

I think this is the is the issue, "Pow_Sw: less than 1v" maybe try hitting power on while monitoring this pin, see if it changes in voltage at all, so power on and power off, see if voltage changes.

[toddw65]

Well, now I can't get the thing to fail. It's firing up properly every time I've tried it over the last couple of days. I did try to monitor that pin and there is a spike but my meter doesn't have the option to capture a peak value and it's too fast for me to tell what it is. Once it settles, it's at ~.88 vdc.

It's a tv I'd picked up and given my daughter months ago so most likely the problem will reoccur as soon as I get it back together and take it to her. 😆

If/when the problem surfaces again, I'll come back to this thread.

Thanks.

[nomoresonys]

Well that's good karma, have you guys helped any old ladies across the street lately, lol.

[toddw65]

Only my wife. Just kidding honey! I meant to say your mom! 🤣🤣

[nomoresonys]

LOL, that cracked me up.