Replace roller rubber on HP 9825 tape drive

Tony Duell ard at p850ug1.demon.co.uk
Sat Jun 18 18:02:52 CDT 2005


> > It's fixed to the motor spindle, and carries a tacho disk (with clear
> > and black lines) at the lower end. This is hidden inside the plastic
> > chassis of the tape drive, between a light bulb and a phototransistor.
> 
> Ok, I didn't realize all that was going on.

HPCC has a reverse-engineered schematic for the 9825 (and for that matter 
the 9815) which would at least show the sensors, etc. There's no 
mechanical info in said schematics, though.
> I had to remove the three screws holding the PCB to the aluminum bracket
> so that I could get to the one screw (of three) that attached the tape
> unit to the rest of the chassis.  Then I could remove the tape unit (after

I _thought_ you could remvoe the complete tape drive/bracket/PCB from the 
keyboard assembly without dismantling it at all, but as I said, it's been 
a long time. Anyway, there's no problem in removing the PCB like you did.

I do know you can remove the tape drives from a 9845 (similar drives, 
very different brackets) without dismantling them, because I did that 
about a week ago. 4 screws and they come right out.


> unplugging the cable).  The aluminum bracket has two screws attaching it
> to the body of the tape unit.  Once those are off, you can extract the
> aluminum bracket and get at the roller and read/write head.  I couldn't
> figure out how to remove the motor so I left it in place.

The motor is mounted to a plastic disk that's fixed to the drive 
(plastic) chassis by 3 or 4 screws. It's on the bottom, the side without 
the head. Undo the screws and pull the motor, complete with the tacho 
sensor and the roller asssembky out.

> 
> I couldn't find any of the recommended materials at the local hardware
> store (never even heard of Tygon) but I did find latex tubing, and I

Does anyone know a UK supplier for similar tubing (in sane lengths, like 
by the metre)? 

> figured that would work just as well as anything.  I cleaned off most of
> the old roller material and decided to leave in place what I couldn't
> scrape off to work as a sort of adhesive (that stuff is sticky).  The
> latex tubing had a 1/4" inside diameter and a 3/8" outside diameter.  The
> diameter of the spindle head is 3/8", so the tight fit gave it added
> traction.  The thickness of the latex tubing is of course 1/8", which is
> about double the thickness of the original roller.  But now the spindle
> was too thick and was wedged against the read/write head.  So I got some
> sandpaper and attached a 9V supply to the motor and lathed it down about

You were lucky (or had spent some time figuring out the wiring, I know 
which I believe). The motor control circuit is not on the tape drive PCB, 
it's on the tape controller (one board up from the bottom in the stack of 
boards in the main chassis). So with the tape drive cable unplugged, the 
motor is electrically isolated and it's safe to connect a supply to it.

The reason I mention this is that on some machines connecting a supply to 
the motor with the controller still connector does nasty things to bits 
of the mtoor controller.

> I re-assembled everything and tested it.  It had trouble at first: the
> drive would start up but then I'd get error 43 (unexpected BOT or EOT or
> tape error).  I kept re-trying and eventually it seemed to work, but then
> I pulled the tape and examined it and it seemed like the tension loop
> inside had come undone.  I opened the tape casing and, being an idiot,
> pulled it apart from the wrong side, and all the internal spindles fell
> out.  So now I have a thoroughly scrambled tape that I now need to figure
> out how to re-assemble (I was supposed to be getting the data off this
> tape).

Ouch. The normal method of dismantling is to undo the screws, then filp 
the catridge over (metal plate on the bottom) and lift off the cover.

To reassemble, the easiest way I've found is as follows :

Put the full spool on its spindle

Add the drive 'puck' (that's the term I've seen in all the manuals), the 
belt and the 2 idler rollers at the front of the cartridige

Put the empty spool on its spindle, then bring the belt round it with 
something like a cocktail stick.

Run the tape round the guids and put the end between the belt and the 
empty spool. Now start turning the drive puck by hand to run the tape 
onto the spool (it is gripped by the belt). Give it about 5 turns round 
the spool, then turn the 2 spools in opposite directions to tension the 
tape. 

Fit the door and its spring. IIRC you can put the spring into the door, 
hook it into a little slot to hold it tenssioned, then drop the assembly 
over the pivot pin and then flick the end of the spring to release it. 

Put the cover on, fit the screws.

I think the DEC TU58 user manual has some instructions for re-threading 
tapes in the back. It's much the same cartridge...

-tony




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