IBM 5155 Manual To Operations page 69

Diagnostic Testing
During the diagnostic tests that follow, you will need a
scratch diskette. If you do not have a scratch diskette,
go to "Diskette Format Procedure" on page Start 40-1.
During the diagnostic tests that follow, you may be
asked to record an error message. This information is
needed when you have your system serviced.
The following are examples of the error messages you
may receive. A message ending in 00 means the test
rmished successfully.
In the following examples X can be any character.
Example 1
XX:XX:XX
ERROR - SYSTEM UNIT XXXX
Example 2
XX:XX:XX
ERROR - EXPANSION UNIT XXXX
Depending on which unit your options or devices are
installed in, the error messages may read SYSTEM
UNIT or EXPANSION UNIT.
January
1984
Test 000-1