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If the voltage is correct, replace the system board.
If the voltage is not correct, the backup battery has
been discharged. Replace the backup battery.
If the backup battery discharges quickly after
replacement, replace the system board.
Checking the Standby Battery
1. Power-off the computer and unplug the AC Adapter
from the computer.
2. Open the keyboard, and remove the diskette
drive/CD-ROM drive, the battery pack, and the hard
disk drive.
3. Remove the top cover and keyboard unit.
4. Open the keyboard unit; then remove the keyboard
card.
5. Remove the standby battery from the keyboard card.
(Refer to “1200 Backup Battery, Speaker, Standby
Battery” on page 425 to remove the battery.)
Warning: Be careful not to cause a short circuit when
measuring the voltage.
6. Measure the voltage of the standby battery.
If the voltage between red and black is 3.5 V dc
or greater, the voltage is correct. Go to step 12
on page 355 to verify standby battery operation.
Wire Voltage (V dc)
Red +2.5 to +3.7
Black Ground
354 IBM Mobile Systems - ThinkPad HMM Volume 3