LG 42LE5400 Backlighting & power supply

[budm]

Re: LG 42LE5400 Backlighting & power supply

I just read the service manual of the 5500, the board is not quite the same as yours, does your board have any label indicating 120V for the LED drive circuit? I wonder if the PFC Boost voltage is not at 390VDC on the two legs of the main filter caps. I would think 109V will not be enough to bias on the LED sting at all.
One statement on page 46 does not make sense, it indicates 6.32V Drop per LED, 19 LEDs per block = 19 x 6.32 = 120V, the calculation is correct but the Vf of the White LED is 6.32V? not typical 3.3~3.6V?

[dkneyle]

Re: LG 42LE5400 Backlighting & power supply

G'Day Bud, By now you'll probably have seen that I have sorted it out (refer to forum post). Yes, that manual I located for the 5500 is significantly different when it comes to the SMPS and the sub-driver board. I had assumed 120 volts because that's what was in that 5500 manual. I've just had a close look at the board and I can't see 120 volts stamped anywhere. I measured the voltage though and it is 116 volts, so perhaps 120 volts (aapprox) is right? Amyway, I'm very happy with the outcome, and in future, before I discard a defective component I'll make sure I really do know what it is!

[budm]

Re: LG 42LE5400 Backlighting & power supply

Oh, so it is working? I thought you still have the backlights problem. I thought the Hot MOSFET is solved only.

[dkneyle]

Re: LG 42LE5400 Backlighting & power supply

I actually had got it to the point where it was operational, backlights were on, it was just that the MOSFET was overheating and was about to destroy itself. If I'd gone to the trouble of actually reading the number on the defective diode I would have saved myself a lot of grief. Hopefully there's lessons here for someone else.

[budm]

Re: LG 42LE5400 Backlighting & power supply

OK, glad to hear that.

[bkamali]

Re: LG 42LE5400 Backlighting & power supply

Does anybody have diagram of YP47LPBD LCD TV Power Supply.
My 47" LED TV powers up with no picture or sound and I need to diagnose the PS.
Thanks in advance

[Alastair E]

Re: LG 42LE5400 Backlighting & power supply

Does anybody have diagram of YP47LPBD LCD TV Power Supply.
My 47" LED TV powers up with no picture or sound and I need to diagnose the PS.
Thanks in advance

Unfortunately, LG do not issue any service info for the PSU's of Any of their sets.

--Best you'll get in their so-called, Service Manuals is the partial Mainboard periferal connections and a basic parts list, with how to use their custom software to interrogate the set--You could write the entire contents on two sides of A4. Utter Crap!

--NOT a Service Manual--Its a Joke!

Ive even sent the UK LG serious complaints about this--which they ignore, But for summit to do, I keep sending them anyway!

--Best start a New Thread on your specific set with its specific fault--Don't forget to add HQ Pictures of the PSU board....

[dkneyle]

Re: LG 42LE5400 Backlighting & power supply

Does anybody have diagram of YP47LPBD LCD TV Power Supply.
My 47" LED TV powers up with no picture or sound and I need to diagnose the PS.
Thanks in advance

If it is a power supply fault they can generally be diagnosed without the original circuit diagram. They are generally all a very similar design. A good tip is, if it uses a multi-terminal regulator device (a power IC with about 6 legs on it) you can Google the type number and often you'll find the spec sheets for the device. The spec sheets will have typical SMPS circuit configurations and you'll nearly always find that the OEM circuit you have is very close if not identical. This aids fault finding greatly.

[hapollo]

Re: LG 42LE5400 Backlighting & power supply

The MOSFET is hidden under the heatsink. It is Q241. The diode in question is next to it, running at an angle. Yes, I think it does go across S & D in actual fact.
Off the top of your head, any thoughts on the correct diode type?
I've seen some images of this board without the diode. Would it be too risky to remove, if only for a short time to check whether the overheating problem goes away?

Got the exact same model with the same problem. Black screen but white lights and LG logo light up when powered up. Just as you described it "(The fancy coloured lights beneath the panel come on and flicker in response to the remote control.)"

Sorry, not clear which solution solved your issue Did you just replace the rectifier D245 and it worked? Or was it the Mosfet Q241?

Did you find the rating of the D245 rectifier?