Lenovo T420 - Manual (Page 40)

Power system checkout
To verify a symptom, do the following:
1. Turn off the computer.
2. Remove the battery pack.
3. Connect the ac power adapter.
4. Check that power is supplied when you turn on the computer.
5. Turn off the computer.
6. Disconnect the ac power adapter and install the charged battery pack.
7. Check that the battery pack supplies power when you turn on the computer.
If you suspect a power problem, see the appropriate one of the following power supply checkouts:
•
“Checking the ac power adapter” on page 34
• “Checking operational charging” on page 34
• “Checking the battery pack” on page 35
• “Checking the backup battery” on page 35
Checking the ac power adapter
You are here because the computer fails only when the ac power adapter is used.
• If the power problem occurs only when the docking station or the port replicator is used, replace the
docking station or the port replicator.
• If the power-on indicator does not turn on, check the power cord of the ac power adapter for correct
continuity and installation.
• If the computer does not charge during operation, go to “Checking operational charging” on page 34.
To check the ac power adapter, do the following:
1. Unplug the ac power adapter cable from the computer.
2. Measure the output voltage at the plug of the ac power adapter cable. See the following figure:
Pin Voltage (V dc)
1 +20
2 0
3 Ground
1
2
3
(20V)
Note: Output voltage of pin no.2 of the ac power adapter may different from the one you are servicing.
3. If the voltage is not correct, replace the ac power adapter.
4. If the voltage is acceptable, do the following:
• Replace the system board.
• If the problem persists, go to “FRU tests” on page 33.
Note: Noise from the ac power adapter does not always indicate a defect.
Checking operational charging
To check whether the battery charges properly during operation, use a discharged battery pack or a battery
pack that has less than 50% of the total power remaining when installed in the computer.
34 ThinkPad T420 and T420i Hardware Maintenance Manual