HP 9875A usable for interchange with 85 or 9825?

Craig Ruff cruff at ruffspot.net
Fri Dec 16 13:04:20 CST 2016

I’m working on getting my 9875A dual DC100A tape drive operational, but have come across a strange issue.  This 9875A seems to have the reversed sense of on which reel the rewind places the tape as compared to my 85B and 9825T (which agree is the left hand one as viewed when inserting the tape into the drive).  I don’t yet know that the 9875A is operating fully, but it passes the non-tape movement selftest.

The 9875A manual mentions it being useful for interchange among systems, and the tape structure (Standard Interchange Format - SIL) matches that of the 98x5 series, and it appears uses the same tape control chip as described in the April 1978 HP Journal article on the 9845.  I guess there could be a failure on the tape control board that is reversing the motor control direction, as both drives behave in the same way, or is causing the firmware to think it is at the wrong end of the tape.

Has anyone used the 9875A in this way?  I was thinking it could be a way to load binary programs into the 9825.

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