Lenovo nm-a161 no backlight

[f-bone]

Hi guys,

I got this motherboard that has picture without backlight.

I measured +LEDVDD at 19V and also other voltages are present at LVDS connector. LID_SW# is at 3.3V and I noticed that BKOFF# is always LOW (0V). I tried new clean ME bios as well.

Any pointers are really appreciated.

BR,
George

[mon2]

Re: Lenovo nm-a161 no backlight

Measure the voltage on LID_SW#, with the LID open. Then repeat with the LID closed.

Any changes to the voltage values?

The LID_SW# must be used by the IT8586E/AX (UE1) to then turn the backlight ON / OFF.

[mcplslg123]

Re: Lenovo nm-a161 no backlight

Ive faced BKOFF# being low on many Lenovo SOC mb's specially on LA-C771P(3-4 units so far). It was SOC fault in my case. I just cut the track of BKOFF# pin from EDP connector, removed the BKOFF# cable from EDP cable and connected it to 3v source from mb. It works now though brightness adjustment is no more available. Try it as a last resort but first findout the reason.

[f-bone]

Re: Lenovo nm-a161 no backlight

@mon2 I measured LID_SW# while the motherboard was on my bench with a LCD connected.. no BKLT.

@mcplslg123 I tried that - I cut the trace going to pin 30 and attached a jumper wire to the LVDS connector directly and to LCDVDD_CON capacitor. No dice.. maybe I should try +3VS?

[mcplslg123]

Re: Lenovo nm-a161 no backlight

@f-bone, you are shorting LCD_VDD to BKOFF# thru that jumper. It wont work. Take +3VS from any other source and connect it to pin30. Hopefully will work. If you have dc supply, then u can inject 3v directly on pin30 and see if u get backlit.

[ktmmotocross]

Re: Lenovo nm-a161 no backlight

# - means that signal is ACTIVE with LOW voltage