820-000426 - no backlight

HI All

PPVOUT_S0_LCDBKLT - 1.3mv
PPBUS_S0_LCDBKLT_FUSED - 12.86v
LCDBKLT_EN_L - 12.72v
PPBUS_SW_LCDBKLT_PWR - 12.87v
PPBUS_SW_BKL - 12.6mv

Is my Q7706 bad or should LCDBKLT_EN_L be a low / 0 voltage?

Cheers,

James

The "_L" denotes an active low signal.
So yes, should be low value there; created by R7701/02 divider.
In fact, you should test LCD_BKLT_EN first.
If OK, then check voltage and diode mode at SCL/SDA kines.

Do you get image at least?
Did you try another (compatible) screen?

As far as I know the screen works.

LCD_BKLT_EN 3.5v
SCL - 4.5 - 3.2v pulsing around ??
BKLT_SDA - 4.5 - 3.2v pulsing around ??

I may be doing it wrong but I get a value of 0 for diode mode to ground on both SCL and SDA

I hope you didn't check diode mode with power applied.
You cannot get voltage on SCL/SDA lines if really have short on diode mode...

Power and battery both disconnected before I changed mode.

Red on the Component End, Black on Ground...

I will have another go tomorrow.

Check always diode mode with red probe connected to ground; sometime need to read viceversa too.
And wait 10-15s after power is removed...

HI,

Thanks for the info. Red to ground!

0.466 on both SCL and SDA.

As LCD_BKLT_EN is good, you should have a bad communication through I2C bus; directly connected to LCD.
Is the only reason for high level at BKLT_SD.

I still recommend to try another compatible LCD assembly...

Confirm no short to ground on backlight output and resistance between pins 9&10 of LED driver is (close to) 0.025 as well.