Lenovo y400 notebook boot no response maintenance

Quickly dismantle the machine, first dry the standby 3 / 5V in the figure below, open the control MOSFET and force it on.Measure the standby 3 / 5V VCC OK, then test the standby and reset of EC, and then check the EC reset is low, and hit 3V linear waveform.The fault caused by the 3V line current of change has been eliminated, and then the 3 / 5V is also current of change. First, disconnect the 3 / 5V isolation point, and then turn off the 3 / 5V. Finally, replace the two pairs of MOSFET of 3 / 5V and power on booting up to remove the fault.

Machine model: Lenovo y400

Machine plate No.: la-8691p

Switch does not respond to standby current.

Maintenance process: first connect the power supply of the repair machine and check it. If there is standby, press the power on key no power on.

Quickly dismantle the machine, first dry the standby 3 / 5V in the figure below, open the control MOSFET and force it on.

Lenovo y400 notebook boot no response maintenance Figure 1

schematic look at the following:

Lenovo y400 notebook boot no response maintenance Figure 2

Of course, the fault is still the same, and then measure the standby 3 / 5V VCC OK, then test the standby and reset of EC, and then see the figure below that EC reset is low.

Lenovo y400 notebook boot no response maintenance Figure 3

In the drawing, search kbrst to quickly find the standby page of EC. For typical RC delay, replace two related Capacitor and resistors directly.

Lenovo y400 notebook boot no response maintenance Figure 4

The fault is still the same. Replace it with an EC and replace it with no power on.

Lenovo y400 notebook boot no response maintenance Figure 5

Re test EC reset or low, with an oscilloscope to see EC reset is such a waveform.

Lenovo y400 notebook boot no response maintenance Figure 6

According to experience, EC reset is generally from the 3V linear delay (this motherboard is not), catch up, hit 3V linear waveform (as shown in the figure).

Lenovo y400 laptop boot no response maintenance Figure 7

Lenovo y400 laptop boot no response maintenance figure 8

Try a standby chip.

Lenovo y400 laptop boot no response maintenance figure 8

After replacing the standby chip, it is the same. Tracing the 3V linear circuit also goes to the RTC circuit. It happens that the CMOS battery has only 0.several v. the diode PD4 to the RTC is disassembled directly, but it is still not well done.

Lenovo y400 notebook boot no response maintenance Figure 9

Lenovo y400 notebook boot no response maintenance Figure 10

Then it summarizes the fault caused by the 3V line current of change, has eliminated the relevant circuit of 3V line, and then measures that the 3 / 5V is also current of change. First disconnect the 3 / 5V isolation point, or the same, and then turn off the 3 / 5V. At this time, 3V linearity is normal. Finally, replace the 3 / 5V two pairs of MOSFET, power on booting up, and remove the fault.

Lenovo y400 notebook maintenance no response chart

Lenovo y400 notebook boot no response maintenance Figure 12

Finally, we summarize the standby chip 3V linear VCC current of change:

1. Standby chip itself (and filter Capacitor).

2. The load is mainly RTC and EC (because the reverse isolation Measuring diode value of RTC is invalid, it can be measured whether the CMOS VCC is low, and the EC is directly removed).

3, 3 / 5 PWM circuit (can be forced to close judgment).

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