Lenovo E15 / NM-C421 Charging Problem

[roman728]

Hello guys,

I have a problem with charging circuit in this laptop. Unit came with no power at all (USB-C meter was cycling turning off and on). I discovered that when I unplug battery laptop works on charger only. So after few measurements I found shorted 1st dual mosfet AONY36324. Unfortunately i was not able to order exact this one, so i ordered AONY36352 which i believe is the similar one. Now the problem is, when i connect battery and charger USB-C meter is not cycling anymore, it starts charging (reading 20V@2,7A) but after few seconds it is going down to 20V@0,20A and laptop switch to battery power. In windows it shows PLUGGED IN, CHARGING but percentage is decreasing. I tried 2nd battery and also replaced BQ25700A and USB-C DC Jack without change. Without battery attached laptop works on charger only. Could AONY36352 be the problem or is there anything else? I am attaching schematics and boardview also.

[MOD EDIT] Link to schematic - https://www.badcaps.net/forum/troubl...74#post1692974

Thanks for any ideas.

[mon2]

It is the replacement dual mosfet. The replacement part is not the same pinout as the original.

[roman728]

Could you please explain where is the difference ?
Ordered exact same mosfet, will arrive in 2-3 weeks. I will keep updated.

[mon2]

See attached. Compare the internal symbols of the dual mosfets against the schematic internal symbols. For starters, review pin # 7. On the replacement, pins 5,6,7 are tied together. This is not the same as the original.

[roman728]

I ordered PQ0204, PQ0205, PQ0201 - exactly same models according schematic. They arrived today, I changed all of them but laptop behaves the same way. Any idea?

[Sephir0th]

Take a look at current sensing around the charging controller. There should be resistors present on these tracks which read low Ohms by design.

[roman728]

Hello, replaced current sensing resistors. There is no change. So today i made some measurements of BQ25700A chip. Results are below.
Laptop is working on battery only, also on charger only. With battery and adapter plugged in, system says charging but percentage is decreasing. Until now i changed PQ0204, PQ0205, PQ0201, USB-C jack, BQ25700, Current sense resistors and battery. Sometimes when i plug in charger, it will start charging for +- 10 seconds (20V@3A).

[Sephir0th]

Very odd measurements. The charging controller forces the battery to power the main power rail even if the charger present.

I think it is time to share pictures which shows the actual physical situation on the PCB.