Expansion Unit 1800 - IBM 3270 Maintenance Manual

If your fixed disk is installed in an expansion
unit, the expansion unit could be the cause of
your problem.
IS THE FIXED DISK INSTALLED IN AN
EXPANSION UNIT?
NO Replace the fixed disk drive adapter. See
Section 5, "Removal/Replacement and
Adjustments"
YES
October
1984 3-1700-21