Lenovo B460 notebook does not trigger repair

Machine model: Lenovo B460

PlateNo.: LA46 DIS 09911_1M

Fault symptom: the notebook does not trigger.

Maintenance process: there is 0.028A on power (I have some problems with this adjustment, and there will be 0.024A display when I don’t use the computer, and all the real ones should be only 0.004A). Press the switch current to run to 0.3A without moving.

Lenovo B460 notebook does not trigger maintenance Figure 1

Lenovo B460 notebook does not trigger maintenance Figure 2

After disassembling the machine, it was found that there were signs of blackening and burning in the lower left corner.

Lenovo B460 notebook does not trigger maintenance Figure 3

After cleaning, several points were directly burnt out. After checking the drawings, U45 is a standby chip, and the component burnt to the right is connected to the 13 pins of the chip with a resistor, and the other should be another voltage divider.

Lenovo B460 notebook does not trigger maintenance Figure 4

Scrape it a little bit and lay down the ground value, and judge that the right side is grounded. Is the chip bad after burning like this? All the feet are grounded, and they are basically normal without short circuit, so make up the bad ones first. However, this 100K resistor is easy to find, and the 249K resistor is not easy to find. I turned over the scrap board and the surprise appeared.

Lenovo B460 notebook does not trigger maintenance Figure 5

The same board, except for the standby chip, is still around, and the right position verifies that my initial judgment is correct.

Lenovo B460 notebook does not trigger maintenance Figure 6

This is what it looks like after the change.

The major inductors were grounded once, so they were powered on and tested. They ran happily to 1.4A, and the screen directly showed that the maintenance was over.