Suggestions for repairing HP tape drive capstans?

[Tony Duell]

> 
> 
> On Apr 18, 2010, at 10:34 AM, Tony Duell wrote:
> 
> > the overall diameter of the tyre is perhaps 18mm (it's going to be  
> > hard to measure, sure the fact I don't have a
> > solid one :-()
> 
> I put a micrometer on the capstan in my 9145A. It had turned to goo,  
> but not melted yet---so it was intact, but difficult to measure  
> without deforming. I got a reasonably accurate measurement off it.  
> Based on experience, this should be close enough to affect a workable  
> repair (though I haven't gotten to actually doing the repair yet).
> 
> 	HP 9145A 36 Track		< 0.800"
> 
> That should be read as "just under 0.8 inch."

0.8" = 20.32mm Maybe the exact size is 20mm. Although I would normally 
expect imperial measurements in an American device, I have noticed that 
all the screws in this drive have metric threads. So perhaps it is a 
sensible diameter in milimetres.

> 
> It was actually harder to clean all the melted capstan residue off the  
> motor spindle than it was to measure it in the first place. It gets  
> EVERYWHERE.

Indeed. The place to keep it well away from is the slotted tachomter disk 
also on the motor spinde.

My method for cleaning invovles a bit of dismantling. Take off the top 
cover and front pneal. Unclip and remove the tape door and its torsion 
spriong. Remove the cotnroller board (athe tope of the unit), then the 4 
screws on the bottom and take the drive mechanism out. Remove the 
board(s) from the underside of the sdrive mechanism.

Take off the microswitch assembly (2 screws, but make sure you know which 
switch goes on top!). Remvoe the optical BOT/EOPT sensor in a 9142. This 
is not essentla but it's fewer things to get gunged up.

Now turn the drive ipside down. See the little plastic part in front of 
the mtoor that hoos into the loading mechanism. Remove this (2 screws), 
then loosen (or remove) the 2 setscrews holding the motor pivot spindles 
in place. Slite out the spidles and lift out the motor assemlby. Recover 
the spirng and 3 insulating bushes. Note that hte motor is insulated from 
the drive chassis (the drive chassis is connected to logic groudn, the 
motor to power groudn, these are connected in the PSU only). Remove the 
tacho senso from the motor (1 screw).

Now clean off as much of the gunge as you can using kitchen paper and 
propan-2-0;. Start with dry paper (it will remove much of the gunge), 
then clean up witht he alcohol. Then connect the motor to a bench supply 
anf give it about 12V (it's not critical). You can now clean it using 
paper or cotton buds dipped in propan-2-ol. You won't get it perfect, but 
it comes a lot cleaner that way.

-tony