You will find many manuals for the 9825 at 
hpmuseum.net  there is a
manual for the base machine and manuals for each of the option ROMs. 
Usable tapes for the tape drive are very rare and for a 9825A there is
only one option for diskettes the 9885.  A machine that says 9825A on
the outside may have been upgrades to a 9825B or T, the 9825T model is
the most useful as it has the maximum memory and has a lot more options
for mass storage.  They are a fun machine I have had a few pass by me,
but no longer have one as space constraints dictated I get rid of some
of my hardware and I opted to kepp my 9835A.
Paul.
On 2024-04-11 8:54 p.m., Andre Lewis via cctalk wrote:
  Howdy all!
 I'm the new owner if one of the coolest "Calculators" HP ever made.
 Everything generally works but I would need a new capstan (rubber is now
 sticky) to use with the tape cartridge.
 I am running into a hard time tracking down information on using it though,
 so if anyone can help fill in some gaps, that would be great!
 I'm looking for:
 - A manual for HPL, the language used to calculate. Things like for loops
 don't seem to work, but 'dsp' 'gto' and variable assignment do.
 - Manuals for any and all of the cartridges, and how to use them
 - Ideas on replacing the capstan
 - Ideas on refurbing the tapes (there's a rubber band equivalent to drive
 the tape on both sides, these have lost their stretch)
 - Specs for the I/O, as I would love to make custom I/O for it.
 I would also love to be able to create new cartridges, but I'm not willing
 to sacrifice any of my existing cartridges to Reverse Engineer them.
 I have the Plotter / GPIO Cartridge, the Mateix cartridge and the Strings
 Advanced Programming.
 Trying to track down an Assembly cartridge or any others.
 Thanks! Any info is appreciated!
 ~ Andre