Shaft encoder in HP2631B printer

[Tony Duell]

This is a long shot... On the other hand, there are people here who've
done all sorts of odd things, and the only silly question is one that's 
not asked (or something like that).

As I mentioned yesterday (when I asked about zneer diode data), I've got 
an HP2631B printer that's gone crazy. I had anohter quick look at it 
today, and it appears that one problem is the shaft encoder on the right 
hand end of the carriage leadscrew. This connects by a 10 way cable 
(integral with the encoder) to the 'printer logic' PCB, 6 of the pins on 
the connector sseem to be used, 2 grouds, 2 +5V and the 2 quadrature 
output signals. Those 2 outputs are buffered by a couple of sections of a 
'14, the outputs of that go to testpoints (and elswehere, of course).

Anyway, both those testpoints are low all the time (turning the leadscrew 
by hand, I've not fixed the motor drive amplifer yet!). The outputs from 
the encoder are high all the time (so the problem isn't the '14, more's 
the pity), they are genuinely high, not floating. And there don't seem to 
be any pull-ups on the printer logic PCB< so the 'high' is coming from 
the encoder.

Anyway. Iv'e read the HP service manual (on http://www.hpmuseum.net) and 
it appears you need special tools to remove and replace the encoder. The 
encoder disk is epoxied to the neadscrew, you need a special puller to 
break the bond and an alignment tool to get the encoder disk the right 
distance insde the encoder housing when you refit it. 

Of coruse I don;t ahve the tools...

Has anyone ever done this? Maybe the same tools, or something like them, 
were used with THe shaft encoders that HP sold as loose componets. Any 
thoughts?

-tony