Lenovo thinkpad L450 motherboard shorted

[Rofix]

Hello everyone I have a problem on the motherboard of my ThinkPad Lenovo L450 there is a short circuit after the second mosfet on the main 19v power supply line, does anyone have the diagram for this board
Motheboard is : AIVL1 NM-A351 Rev .1 .
Thanks for the advice and help

[mon2]

Review the charger IC and the 2nd mosfet itself. Do you have REGN voltage? ACDRV voltage on the gate of the DCin mosfets?

[mcplslg123]

If you have short circuit after 2nd mosfet,then its wiser to measure the same on CLR and then proceed to desolder it and inject 1V/5A on the shorted side to find out what is shorted.

[Rofix]

hi, on PU7 at pin 24 REGEN I find 6 Volt on pin 4 ACDRV the voltage fluctuates, it is around 0.150 Volt, on the gate of the main mofets PQ20/PQ21 the voltage varies around 0.150 Volt there too

[mon2]

Your 2nd DCin mosfet is probably defective so do review the advice in post # 3.

Carefully, flux and remove the 4k resistor that is in series between ACDRV and the gate pins of the DCin mosfets. After this series resistor is removed (do not lose this resistor) - power up again and measure the voltage output @ ACDRV charger pin # 4.

Is ACDRV now ~25 volts?

[Rofix]

Hello i remove the 4k resistor but the voltage output @ ACDRV charger pin # 4. is 0 volt

[mon2]

Measure the voltage to ground very carefully of:

ACDET ; must be > 2v4 to enable the dcin mosfets
ACOK ; expected to be a logic low since main power rail is missing and this line is pulled to the missing +3VALW
CMSRC ; used by the charger ic to create the boosted ACDRV voltage

remove all power, meter in resistance mode. Measure the resistance to ground of the main power rail.

Post each measurement.

[Sephir0th]

The main power rail is suspected of being short-circuited from the beginning with regard to the initial posting. I don't really understand why you're tinkering with the mosfets here instead.

Proceed like advised from mcplslg123 already. Normally it is not even necessary to remove any component to find the faulty part with voltage injection.

[Rofix]

hello
ACDET ; 2,4 Volt
ACOK ; 0.003 Volt
CMSRC ;0.006 Volt

resistance to ground of the main power rail after the second mosfet is 0,6 Ohm

[mon2]

Ok. As per post # 3, inject a 0v8 to 1v0 voltage onto the main power rail @ 3A-5A. We use a dedicated tool from Aliexpress (short killer) that spikes upto 30A of current. Often around 5A-8A the shorted part cracks / smokes open. Usually it is a shorted tantalum or ceramic cap. Hope it is the same for you. If you have a thermal camera, it will help to isolate the part. Be sure to check both sides of the PCB. If a high side mosfet is leaky on the board, it may have killed the CPU so do consider to remove the heatsink off the CPU for the heat inspection. First, just check around the board for a defective cap. You can use IPA (alcohol) to locate the defective part. Wherever the IPA evaporates, you have heat.

[Rofix]

Hi, while doing an injection I found this component that overheated a lot PU 10

[Sephir0th]

Something is odd. Why does the NM-A351 schematics, i sourced, does not fit to the Silk screen print?

However, from location this smells like 1.05V supply. A proper prayer that the coil does not measure below 10 Ohms and then replace the controller.

[Rofix]

You probably also found the AIVL2 NM-A351 Rev .1 schematic.
for my card I need the AIVL1 NM-A351 Rev .1.
Unfortunately I also find 0 Ohm on the reel