Lenovo ThinkCentre M75n, Hardware Maintenance Manual, Page: 45 / 120

Message/Symptom
FRU/Action
Serial or parallel connector device failure (adapter
connector)
1. External Device Self-Test OK?
2. External Device
3. Cable
4. Alternate Adapter
5. System Board
Some or all keys on the keyboard do not work
1. Keyboard
2. Keyboard Cable
3. System Board
Undetermined problems
This section provides instructions on how to find out the failing devices or adapters.
1. Turn off the computer.
2. Remove or disconnect the following components (if installed) one at a time.
a. External devices (modem, printer, or mouse)
b. Any adapters
c. Memory modules
d. Extended video memory
e. External Cache
f. External Cache RAM
g. Hard disk drive
h. Diskette drive
3. Turn on the computer to retest the system.
4. Repeat steps 1 through 3 until you find the failing device or adapter.
If all devices and adapters have been removed, and the problem continues, do one of the following to
replace the system board.
• For fan models, see “System board” on page 79.
• For fanless models, see “System board and coin-cell battery” on page 101
Chapter 4
.
Service checkout and symptom-to-FRU index
39