Lenovo s400 - no video on lcd only backlight, on external is ok

[ktmmotocross]

Hello.
Have this Lenovo s400 that have no video on lcd only backlight. on external is everything ok. i try to measure voltage pins and only voltage that looks off is +LCDVDD_CONN which is 0.4V. when i remove L29 i have 3,12V on first pin and 0.4 on second pin.
i have board rev. 1.0 and schematic is rev 0.1

any hints?

[piernov]

Re: Lenovo s400 - no video on lcd only backlight, on external is ok

What's the resistance to ground on +LCDVDD_CONN with and without LCD connected? And resistance across L29?

[ktmmotocross]

Re: Lenovo s400 - no video on lcd only backlight, on external is ok

4.4kohm with and 200kohm without lcd

[lorins_core]

Re: Lenovo s400 - no video on lcd only backlight, on external is ok

i think you need to test a good panel. my opinion need to replace. respect to you my friend.

it is good to repair for experience.
well maybe the TCon. maybe some capacitor near or filter caps have leak.

wait. need to check also the IC. i dont know what brand. can you send a picture here. to identify

[ktmmotocross]

Re: Lenovo s400 - no video on lcd only backlight, on external is ok

removed both capacitors after coil L29 but nothing changed

replaced panel and cable, but still the same

[JaroTech]

Re: Lenovo s400 - no video on lcd only backlight, on external is ok

Have you tried to replace Q72?

[SMDFlea]

Re: Lenovo s400 - no video on lcd only backlight, on external is ok

What model number is the panel , is it n140bge-lb2

[ktmmotocross]

Re: Lenovo s400 - no video on lcd only backlight, on external is ok

just jumped that q72 and displey start to show screen. thank u guys. now i replace him

[peste]

Re: Lenovo s400 - no video on lcd only backlight, on external is ok

remove the LVDS cable from the motherboard connector, start the laptop and measure the voltages on the plug, if ok the problem is the cable or display ...