Lenovo L40 - only pulsing ACIN

[ktmmotocross]

Hello.
Have this Lenovo L40 that have pulsating VIN. I found that on Charger ic i have only little bit pulse to 3.5V on 88731_ACIN. But when i poking around and measure ohm/not diode mode/ and put blackprobe to ground and red to side of PR100 all start to work and 88731_ACIN goes steady to 4V. after power reset it is same again. Wonder why it can act like this?

[mcplslg123]

Re: Lenovo L40 - only pulsing ACIN

Got a somewhat similar case last week. It was sony mbx270 with pulsating +19V rail(Laptop boots from a charged battery). The voltage divider circuit has 4 resistors 45K,45K,69K,435K. took all of them out and measured to findout all re ok. Soldered them back and it worked but after 30 mIns -same story of pulsing B+. Ultimately replaced all the 4 resistors and its working fine for last 5-6 days. Dont know why....

(Charging Ic was installed new, so it was not charging ic)

[mcplslg123]

Re: Lenovo L40 - only pulsing ACIN

Here is the pic

[ktmmotocross]

Re: Lenovo L40 - only pulsing ACIN

i quit from make proper repair. it have broken display so i wont bother with it. i removed pq12 to have stable 88731_ACIN. battery is charging, works without/with power so no other repair needed.

[Spider1211]

Re: Lenovo L40 - only pulsing ACIN

I had a similar issue recently on an Asus, my issue was a shorted MOSFET on the battery charger side.