The library error we were getting :

ANR8300E I/O error on library STKLIB (OP=00006C03, CC=304,
 KEY=04, ASC=40, ASCQ=02, .... Description=Changer failure).

appears to have been caused by one of the DLT7000 drives getting
stuck in the 'handle down position'. This prevented tapes being
loaded into drive. Our engineer was able simply to manually put
the drive into 'handle up position' in which tapes can be loaded.

Diagnosis of this was confused by the rash of other errors preceding
this which I can only assume were caused by problems on the SCSI
bus - which was resolved eventually by reseating all the cables ( and/or
numerous reboots of library and server ).

I would still be interested in how you determine whether your drives
have the power supply problem described elsewhere - if anyone happens
to know.

+----------------------------------------------------------------------+
 Steven Bridge     Systems Group, Information Systems, EISD
                          University College London
 email: s.bridge AT ucl.ac DOT uk                   tel: +44 (0)20 7679 2794