Symptom/Error FRU/Action
LED for hard disk drive is
not working, but the 3550
Expansion Unit is
completely functional.
1. System Board of
3550 Expansion Unit
Undetermined Problem
Use the following procedure when the diagnostic tests do
not identify the failing adapter or device.
Check the power supply (see “Power Systems Checkout”
on page 327). If the power supply is operating correctly,
return here and continue with the following procedure.
1. Power-off the 3550 Expansion Unit.
2. Remove or disconnect one of the following adapters
or devices. (Do not isolate adapters or devices that
are known to be good.)
a. Non-IBM devices
b. Modem, printer, mouse, external keyboard,
external display, numeric keypad, or other
external devices
c. Any adapter
d. SCSI device
3. Power-on the 3550 Expansion Unit and reconfigure
the system.
4. Run system checkout (see Step 016 on page 319). If
diagnostic tests cannot be loaded from the computer
hard disk drive, load and run the tests from the
Reference Diskette. Test only those adapters and
devices still attached to the 3550 Expansion Unit.
5. If the symptom remains, repeat steps 1 through 4
until you find the failing adapter or device.
6. If the problem remains, replace the system board of
the 3550 Expansion Unit.
Expansion Unit (3550)
333
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