Lenovo ThinkPad P50 Notebook no booting repair

Machine model: Lenovo ThinkPad P50

Main board version number: NM-A451

Malfunction: Notebook no booting

Maintenance process:

I received a Lenovo ThinkPad P50 notebook computer, the fault description notebook no booting, CPU Short circuit,Connect the power supply large current.

Lenovo ThinkPad P50 Notebook no booting repair Figure 1.

Simple investigation, breakdown of isolation tube.

Lenovo ThinkPad P50 Notebook no booting repair Figure 2.

Lenovo ThinkPad P50 Notebook no booting repair Figure 3.

Lenovo ThinkPad P50 Notebook no booting repair Figure 4.

Remove the public terminal VINT20 of PL23 PL24 instead of Short circuit, which means that it is the chip P U5 Short circuit of VCCCPUCORE VCC. At the same time, both VCCSA and VCCCPUCORE diode value to the ground are measured to be 0 ohms, which basically determines that the CPU has burned out.

Measure VCCSA to ground diode value.

Lenovo ThinkPad P50 Notebook no booting repair Figure 5.

Lenovo ThinkPad P50 Notebook no booting repair Figure 6.

Go to BGA Rework Station and remove the CPU perfectly.

Lenovo ThinkPad P50 Notebook no booting repair Figure 7.

Measure the ground diode value again.

Lenovo ThinkPad P50 Notebook no booting repair Figure 8.

The VCCSA ground diode value returned to normal.

Lenovo ThinkPad P50 Notebook no booting repair Figure 9.

VCCCPUCORE diode value to ground returns to normal, replace PU5 chip which is confirmed to be OK, and turn on the power to see the current.

Lenovo ThinkPad P50 Notebook no booting repair Figure 10.

After the standby current reaches 30mA for a few seconds, it drops to 8mA. After the standby self-test is completed, 3.5 m normally drops to 8mA, 3m 5m switch is generated again.