Lenovo Xiaoxin 15 2019CPU frequency down lock 0.4GHz (overheating detection signal is pulled down)

Lenovo Xiaoxin 15 2019CPU frequency down lock 0.4GHz (overheating detection signal is pulled down)

Lenovo Xiaoxin 15 2019, the fault is that the CPU down frequency locks 0.4GHz. This kind of frequency reduction and frequency locking is usually caused by a problem with PROCHOT’s signal. We can find it directly.blueprintTo determine the signal position to repair, how to operate specifically, see the following detailed explanation!

[Fault model] Lenovo Xiaoxin 15 2019

[Fault phenomenon] CPU frequency down lock 0.4GHz

[Maintenance process] I received a machine sent by a customer for repair, the model is Lenovo Xiaoxin 15 2019, and the fault is that the CPU frequency reduction lock is 0.4GHz.

Lenovo Xiaoxin 15 2019CPU frequency down lock 0.4GHz Figure 1

This kind of frequency reduction and frequency locking is usually caused by a signal problem of PROCHOT, so we directly find the drawing to determine the signal position for repair.

Lenovo Xiaoxin 15 2019CPU frequency down lock 0.4GHz Figure 2

Lenovo Xiaoxin 15 2019CPU frequency down lock 0.4GHz Figure 3

After reading the drawings, there is no point, but there is a principle. Basically, this signal goes to the charging IC, CPU power supply chip, EC and CPU. It is measured that this signal is pulled down to 0, and the resistance value is normal. Let’s just eliminate it one by one. The method is very simple. Just disconnect this line to the chip or remove the chip, and we can’t disassemble the CPU. So we use blades to cut off the lines to the charging IC and CPU respectively, and then see who pulls down the power supply.

Lenovo Xiaoxin 15 2019CPU frequency down lock 0.4GHz Figure 4

Lenovo Xiaoxin 15 2019CPU frequency down lock 0.4GHz Figure 5

Disconnected, it was found that the PROCHOT voltage of 3.3V came out as soon as the line on the CPU power supply side was cut off, indicating that the CPU power supply IC was damaged, so I directly ordered a new chip to replace it, and the frequency was no longer locked after the chip boot test.

Lenovo Xiaoxin 15 2019CPU frequency down lock 0.4GHz Figure 6

[Maintenance result] The mainboard was installed, and the startup test was successfully lit. The recording, camera, sound and WiFi of the system test were normal, and the stress test of the baking machine was normal for half an hour. The maintenance was over.