dell 3521 la-9104p no backlight

[doctormasry]

hellolaptop dell 3521 la-9104p no light on screen
i can see data ok but no backlight
on jlvds
NV_PWR_SRC 18 v is ok
3vs is ok 3.3
lcdvdd is ok 3.3

i replacd led screen
and change flata ( caple between board and led )
any idea

[khaahk]

Voltages on:

pin36 INV_PWM
pin37 DISPOFF#

[doctormasry]

Voltages on:

pin36 INV_PWM
pin37 DISPOFF#

thanks
pin36 2.5v
pin37 0 volt

[mon2]

pin37 DISPOFF# = the '#' denotes an ACTIVE LOW signal. So with 0v here, the logic board is requesting to turn the DISPLAY OFF.

[doctormasry]

pin37 DISPOFF# = the '#' denotes an ACTIVE LOW signal. So with 0v here, the logic board is requesting to turn the DISPLAY OFF.

i connect pin 37 with 3 volt
but the same problem data without backlight

and there is data on screen

[mon2]

Locate the jumper @ RV29.

Cut with a sharp knife to isolate the INV_PWM trace. After this cut, INV_PWM should be with only the pull-down resistor @ RV230.

Measure the voltage on INV_PWM which should be 0v since it is not being driven.

After this confirmation, take a piece of wire and attach to INV_PWM and 3v3. This should drive the PWM to full ON state for the backlight. If this does not work, then your backlight inside of the display assembly is defective. That is, there will be another circuit inside of the display assembly that accepts the PWM (pulse width modulation) signal to drive the multiple leds behind the LCD panel itself.