What is the function of the blue LED on a LG-Philips inverter board?

[tom66]

I've got the famous LG-Philips master-slave inverter (6632L-0470A) with no backlight, not even an attempt to strike the backlight or a 2sec to black symptom. In my case, a blue LED lights up on master then goes out slowly. Disconnecting the slave results in no LED and no backlight either.

Wondering what the purpose of this LED is.

So far I've noticed no gate waveforms to the FETs and the CT voltage does not oscillate as I would expect.

I do have some IC function the Duty Out is working as is the respective oscillator and onboard Vreg voltage.

24V and BLON are present, DIM PWM has a square wave, DIM waveform changes as TV boots.

Have already swapped BD9897FS as I suspected this to be the cause but to no avail.

Anyone have a working set remember what the LED should do when the inverter works? Or some documentation on it?

TV: Philips 42PFL9632D

Thanks

[tom66]

Re: What is the function of the blue LED on a LG-Philips inverter board?

Ah hah... I checked the VREG pin of the IC on the Slave it has 60 ohms to ground... the IC is shorted internally. This is the Vdd supply for the internal logic of the IC. Without the slave IC functioning, the oscillator on the master will not work (the SRT pin of each board is pulled down by the respective inverter in this design; if that does not happen, the inverters will never oscillate...)

I think this could cause the fault. As a quick test, I'm hoping the MASTER chip I have pulled was good anyway. I'll swap the chips over, and see if the problem is resolved.

[tom66]

Re: What is the function of the blue LED on a LG-Philips inverter board?

Fixed. The master chip worked on the slave board. Backlight working perfect and the ambilight looks nice on this set, first I've fixed a set like this. The 100Hz interpolation is lousy like most although this one is particularly bad, everyone looks like they are puppets on a fixed background, and any movement freaks out the deinterlacer. NXP PNX5050 processor.

Also, the blue LED does exactly what it did before. Lights up then goes dim... so not sure if it is supposed to indicate anything.

I am also going to apply the modification II to these boards to prevent future failure.

[Alastair E]

Re: What is the function of the blue LED on a LG-Philips inverter board?

Hmm......

What is--

'The Modification II'.....?

[tom66]

Re: What is the function of the blue LED on a LG-Philips inverter board?



Reliability improvement