Asus U4000U notebook does not trigger repair

Asus U4000U notebook does not trigger repair.

Machine model: ASUS U4000U

Board number: UX310UV 2.0

Fault phenomenon: the notebook does not trigger.

Maintenance process:

An ASUS U4000U laptop can’t be turned on. Plug-in measurement EC AVCC power supply +3VA_EC is constantly jumping high and low, so is EC_RST#. Watch the waveform with analog oscilloscope.

Asus U4000U notebook does not trigger maintenance figure 1

Check that the source of +3VA_EC is converted from PU8801.

Asus U4000U notebook does not trigger maintenance figure 2

EN1 PS_ON of PU8801 turns on +3VA to +3VA_EC, the PS_ON is emitted by EC, and the PS_ON voltage keeps jumping, which seems to be a PS_ON problem.

Asus U4000U notebook does not trigger maintenance figure 3

The voltage waveform of PS_ON_EC is also a jump. Check the conditions for EC to issue PS_ON_EC.

The reset of EC and AVCC can only be generated after +3VA_EC. Check the signal pulled up by +3VA, and the EC pulled up or powered up by +3VA is as follows:

Asus U4000U notebook does not trigger maintenance figure 4

The VSTBY0 power supply is normal, PWR_SW# and LID_SW# have 3V high level, and AC_IN_OC# has 0V low level.

Under normal circumstances, after the EC is powered by VSTB0 deep sleep, when the battery is plugged in, the high-level LID_SW# and PWR_SW# with normal jump will send out the high-level PS_ON_EC; when the battery is not plugged in, the normal low-level AC_IN_OC# and the high-level LID EC will automatically send out the PS_ON_EC, and ASUS will generally start automatically without plugging in the built-in battery.

The resistance value of +3VA is normal and the voltage is normal, so it is suspected that EC is damaged. Replace EC directly.

Asus U4000U notebook does not trigger maintenance figure 5

After the change, it will be automatically powered on. When it is powered off, the machine will be turned on. The installation test is OK, and it is perfectly repaired.