Samsung LE40R71B no backlight

[mij59]

I am trying to repair a Samsung LE40R71B, the backlight inverter doesn't work.
All the supply  voltages are present , no bad caps, or solder joints found, got sound and can see a picture when the lcd is lit with a flashlight.
On power on the backlight doesn't light up briefly.

I have attached the schematic of the power supply board BN44-00134A, the problem is with IC1801 (LX1691A) the outputs AOUT and BOUT remain low.
On power up the input ENABLE goes high (5V), but this has no effect on AOUT and BOUT.

On the power supply board IC1801 is actually a MSC1691AI, I replaced it with one ordered from e-Bay, but AOUT and BOUT seem to be floating.
I've also attached a block diagram of the MSC1691AI, the working is not clear to me, e.g. there is no clock signal on DD_CLK.

Google search on the topic without result so far, any input greatly appreciated.