HP 21mx on epay

[Mike Loewen]

On Thu, 5 May 2005, Lee Courtney wrote:

> This looks a lot like a development system we'd have in the RTE Lab in the
> late 70s/early 80s. 7925s were 120MB removeable packs, 7920s were
> 100MB(IIRC). Across a string of several drives I remember 7925s having
> fairly frequent head crashes - maybe on the order of one every 6 months or
> so.

    The 7920s were 50Mb.  The head crashes had a lot to do with how clean 
your computer room was.  I used to work for a company doing 3rd party 
maintenance on HP3000 systems.  We had a couple of customers who installed 
a humidifier in their computer room, unfortunately the type that left a 
fine white powder residue.  I ended up replacing multiple heads in the 
7925s and practically disassembling them to clean them up.  The white 
powder goes straight through the foam filters.

    As I recall, the usual cause of head failure on the 7920s and 7925s was 
one of the wires to the head breaking.  They could be replaced and aligned 
without too much pain, with an alignment pack and a scope.


Mike Loewen				mloewen at cpumagic.scol.pa.us
Old Technology	http://ripsaw.cac.psu.edu/~mloewen/Oldtech/