Sony KD-55X8507C Completely dead

[Zaprodk]

Hi.
I have a Sony KD-55X8507C on the mending table today.

It appears completely dead, no status LED's lighting up. Even though it's acting completely dead, the power supply is running and the heatsinks on the main ASIC's do heat up, so it's just not starting properly.

This thread has been a lot of help since someone posted an excerpt from a schematic that contains the correct LED driver chip. without that pinout, anyone's guess

The power supply has two boost converters, each run 5 strings of LED's. All LED strings i tested to have a Vf of 87V@1mA, so they are all good.

All DC voltages looks OK. The supply for the LCD boost converter is 61V. The booster is NOT running. I tried pulling BL_EN and DC_DIM to 3.3V to enable the booster. The signals get all the way to the LED driver (CXA3854) pin 5 and 11 and it has the prerequisite 12V supply on pin 24 as well.

I tested all FET's, diodes etc in the booster. All seems good.
Nothing looks, burned, only the PCB around the two FET's is slightly discoloured.

I have no gate pulses on pin 26 on both the driver chips.

So this suggests dead chips i guess, but why would both die at the same time?

Any suggestions what to check before i order some new chips?

Thanks in advance!

// Per.

[dick_barton]

Re: Sony KD-55X8507C Completely dead

Did you measure the resistance between pins 23 & 24 as per the other thread. Out of curiosity what is the Vref voltage

[Zaprodk]

Re: Sony KD-55X8507C Completely dead

Did you measure the resistance between pins 23 & 24 as per the other thread. Out of curiosity what is the Vref voltage

Resistance is Approx 300/500Ω each direction, dancing a lot up/down from caps charging up.

Vref is 4.98V

Since i don't have the datasheet for the IC i have no idea what Vref should be.

// Per.

[dick_barton]

Re: Sony KD-55X8507C Completely dead

The 5V Vref looks like a reasonable value. When Vref is a rediculously low value it can be a clue to the IC being faulty. The 300 to 500 ohms doesn't seem too bad a resistance reading.

Are the two boost converters you refer to both CXA3854 devices?

[Zaprodk]

Re: Sony KD-55X8507C Completely dead

Are the two boost converters you refer to both CXA3854 devices?

Yes.

// Per.

[dick_barton]

Re: Sony KD-55X8507C Completely dead

Have you compared the voltages against each other?

[Zaprodk]

Re: Sony KD-55X8507C Completely dead

Have you compared the voltages against each other?

Yes.

The voltages on both chips are identical +/- some mV.

I̶ ̶w̶o̶u̶l̶d̶ ̶t̶h̶i̶n̶k̶ ̶t̶h̶a̶t̶ ̶m̶o̶s̶t̶ ̶o̶f̶ ̶t̶h̶e̶ ̶i̶n̶p̶u̶t̶ ̶s̶i̶g̶n̶a̶l̶s̶ ̶o̶n̶ ̶t̶h̶e̶ ̶c̶h̶i̶p̶s̶ ̶a̶r̶e̶ ̶d̶i̶r̶e̶c̶t̶l̶y̶ ̶i̶n̶ ̶p̶a̶r̶a̶l̶l̶e̶l̶ ̶o̶n̶ ̶t̶h̶e̶m̶.̶

Edit:
Pins 5, 10, 11, 12 and 25 is shared on both chips (apart from supply voltage ofc.)

// Per.