IBM 6648 - Manual (Page 44)

If the printer self-test runs correctly, install a wrap plug in the parallel port
and run the diagnostic tests to determine which FRU failed.
If the diagnostic tests (with the wrap plug installed) do not detect a failure,
replace the printer cable. If that does not correct the problem, replace the
system board or adapter connected to the printer cable.
Power supply
If the power-on indicator is not on, the power supply fan is not running, or
the computer will not power-off, use the following procedures.
Check/Verify FRU/Action
Check the following for proper installation.
v Power Cord
v On/Off Switch connector
v On/Off Switch Power Supply connector
v System Board Power Supply connectors
v Microprocessor(s) connection Reseat
Check the power-on switch for continuity. Power Cord
Check the power-on switch for continuity. Power-on Switch
If the above are correct, check the following voltages.
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Hardware Maintenance Manual: IBM NetVista Computer Types 6058, 6059, 6269, 6568, 6569, 6578, 6579, 6648,
6649