HP-85A tape drive conversion

Rik Bos hp-fix at xs4all.nl
Wed Apr 1 04:13:43 CDT 2015

> -----Oorspronkelijk bericht-----
> Van: cctalk [mailto:cctalk-bounces at classiccmp.org] Namens Jay West
> Verzonden: woensdag 1 april 2015 2:16
> Aan: 'General Discussion: On-Topic and Off-Topic Posts'
> Onderwerp: RE: HP-85A tape drive conversion
> Rik wrote...
> ----
> But this type of drive has issues about the running off the tape every
once in a
> while.
> Somehow the tape end detection not always detects the end of a DC2000
> It suspect the tape controller hardware, but I didn't researched it so
it's for the
> best an educated guess.
> ----
> A quick read through the assembler manual for the 85 throws up all kinds
> cautions specifically about assembly code causing issues with the tape
> off the spool, seemed a known issue. Just saying - it may be a software
issue not
> a hardware issue.
> J


I think there is some confusion, the HP-85 QIC modification I wrote and
placed at the HP-85 Yahoo group works. 
The change of the resistor is necessary to increase the write current, to
compensate the higher permeability of the DC2000 / QIC40/80 tapes.

The HP 98X5 series and the HP 264X terminals are using another type of drive
and different controllers then the HP-85.
Issues here are:
HP 9825 A/B/T and HP 9831A spurious tape roll-off's  (tape winding of the
reel when rewinding)
HP 9835/45 all types, QIC tapes can't be formatted because the internal tape
counter (controller chip) gets an overflow due to extended tape lenght. Can
be solved by virtually shortening the tape by making new EOT holes.
HP 264X basic test works but I did no extended testing because I got some
DMA problems with the terminals, but the tape speed is much higher as the
speed of the HP-85.

Write current to use the QIC tapes instead of the original HP tapes is
always higher, the article describes how to do this for the HP-85 and HP
9825/31 series.


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