Lenovo ThinkStation S20 4157 Hardware Manual page 98

3. Power-on the computer to re-test 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, replace
the system board.
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Hardware Maintenance Manual
c. Memory modules
d. Extended video memory
e. External Cache
f. External Cache RAM
g. Hard disk drive
h. Diskette drive