GND

Password-Override

Connecter

VC VB VG VA

PWRGOOD

Note:

Only

VOLT

is

marked

on the

system

board.

 

Use the above figure to

locate

the

VA, VG,

 

VB, VC,

and

PWRGOOD

signal

names.

 

 

Ÿ

If

all

voltages are

correct, the

voltage

converter

 

is

operating

correctly.

 

 

 

ŸIf the voltages are not correct, go to the next step.

8.Power-off the computer and unplug the AC adapter

cable

from

the computer.

9. Check

for

a short circuit between GND and VA, VG,

VB,

or

VC.

 

ŸIf there is a short circuit, replace the following

FRUs one at a time to correct the problem.

–Voltage converter

–System board

Ÿ If

there

is

no

short circuit,

go to the next ste

10. Check

the output voltage of the AC adapter cable

(see

“Checking

the

AC

Adapter” on

page 72).

ŸIf the output voltage is correct, go to the next step.

11. Replace the following FRUs one at a time.

–Voltage converter

–System board

Checking the Voltage Converter (720,

720C): Use the following procedure to isolate a problem with the ThinkPad 720, 720C voltage converter.

1.Power-off the computer.

2.Power-off all attached devices and disconnect them from the computer.

3.Unplug the AC adapter cable, then remove the battery pack from the computer.

4.Carefully place the computer bottom-side up and remove the bottom cover.

5.Plug the AC adapter cable into the computer.

78 IBM Mobile Systems HMM