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case study

problem----dimm display no backlight

[hidden]model- lenovo ideapad s300

BOARD PART- VIUS3/VIUS4 LA-8951P


diagnosis


checked with other cable and led same result dimm display

this cable and led working fine in other board


then i confirm board issue


then check for voltage in lvds conector

found led voltage 18v ok

found lcd_vdd 3.3v ok

pin 37 of led voltage ok 3.3v

but only missing pin35 of invt_pwm 3.3v which enable the led light ( EN_LED MISSING)


which is coming from pch and signal name as pch_pwm which is not avilabe 3.3v

i just put jumper from pin 37 to pin 35 of lcd and BACK ligt on ( THIS IS FOR TESTING PURPOSE)

then i trace found pch issue

but this board have two invt_pwm one is coming from pch_INVT and other is coming from ene io ec_invt_pwm

EC_INVT_PWM not conected just optional in resistor place r14651


RESULATIONNNNNN


so just remove resistor r14631 and conect it to the place of r14651 which one is connect to lvds1 in pin8

and which is goes to pin35 of led

now laptop working fine

and backligt goes onnnnnnnnnnn[/hidden]

But Sir i think brightness will not vary.it will fix at high

ganeshcell wrote:But Sir i think brightness will not vary.it will fix at high

you are absoulatly right but it is pch issue and needed to replace PCH and it wiil more cost and risk so that i am doing this job................to just make working condition

Well done

gooooooooooood troubleshooting

good job sir.

good but not best

PINTUSINGH wrote:good but not best

thank you sir

but sir plz guide me to do best

sir how it will best plzzzz sir

Don't you think this is bad connection at PCH rather than PCH going bad? Did you check for open traces?

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