19 Aug
2013
19 Aug
'13
6:19 a.m.
The knob is like a mouse or a track ball. It produces a quadrature
signal on two wires.
From this, one can determine both speed and direction.
I just replaced two such knobs on my Nicolet 490 scope I just
got. I don't think the ones I have are the same as the ones on
the HP but work on the same principle. I got what I need from
Mouser. Mine used mechanical switches rather than optical.
To see if it is working, put a meter on the leads. If it is working
you should see levels from the optical detectors going
high and low on at least two of the leads, when the knob is turned.
Tinker Dwight
Date: Sun, 18 Aug 2013 20:45:32 -0700
From: derschjo at gmail.com
To:
Subject: Re: HP 98203 keyboard "knob" debugging
On 8/18/2013 12:17 PM, Tony Duell wrote:
I appreciate it, thanks.
Thanks to
a tip froma list member, I managed to snag a compatible
keyboard for my HP 9816 -- a "Nimitz" class keyboard, the
98203B(http://www.hpmuseum.net/display_item.php?hw=682).
It works fine (though it dwarfs the machine it's connected to) except
that the "knob" in the upper-left does not appear to function. I've
looked for service manuals but I can't find anythingthat's particularly
detailed.
I've partially disassembled the knob unit-- there's a glass/ceramic disc
with radial markings, and with what appearsto be an incandescent bulb on
one side and a pair of sensors on the other. The bulb does not appear to
be illuminating when powered up (it does seem to be getting 5V),so this
seems suspect but I don't know whether it's supposed to be emitting
visible light or not. I also don't know what to replace it with.
Anyone repaired one of these before?
I'm guessing Tony'll havesome input here :).
Given the flamage last time I
talked about HP machines here, I am not
sure I do want to post anything. On the other hand, I guess I should try
to help...
I have a 9816, it's aan interesting little box. But I have the original
'compact' keyboard on mine, I've never seen the one you have, and thus
don't have a shcematic of it. The HP service manuals for all HP9000/200
machines (AFAIK) were boardswapper guides with no schematics, although
there can be usefukl inforamtion in them (the 9826/36 manaul does have
pinouts of all the internal connectors, for example). I don't have the
9816 manual, is it on the web somewhere?
I don't think I've found the 9816-specific manual anywhere, no.
What I can tell you is a little about the 'compact' keybaord, in the hope
that yours is related. At least the interface to the host should be much
the same.
The 'compact' keyboard is stuffed with 4000-series CMOS ICs. Whether HP
did the sensible thing (for them, and a pain for us now) and used a
microcontroller in the later keybaord I do not know. What does your
keybaord contain in ternms of ICs?
There's a small PCB labeled 98203-66501 mounted to the bottom of the
chassis; the keyboard PCB is plugged into it via a ribbon cable. It's
full of ICs, though they appear to be labeled with HP's custom numbering.
The knob is read out as 8 (I think) consecutive 'keys'. 7 bits are number
of pulses from the knob, one bit is the direction. There is a misfeature
here, in that the counter used is not bidriectionsal. So if you turn the
know 3 pulses one way, 4 pulses the other, the counter will say 7 pulses,
the direction bit will be the last direction the knob moved. Not the
correct reuslt of '-1 pulses moved'. Fortunately the keyboard is scanned
sufficiently often that this is not a real problem. I would have expected
HP to get it right though!.
The actual knob is an HP optical shaft encoder unit. It has 4
conenctions. Ground, power (I think 5V, maybe 12V) and 2 outputs. THese
are square waves in quadrature, in the normal fashion. The outputs may be
open-collector, if so they will be pulled up on the logic board. I think
what I would have done, before pulling the encoder apart, is to stick a
'scope or logic analyser on those signals and turn the knob to see if
anything is coming out.
Without knowing the pinouts I was hesitant to start prodding at things.
Besides, the rear cover just snaps off, it's easy to look at :).
As you have discovered these enocders do come apart. The light source is
an IR LED (so if you've put 5V striaght acorss it it's probably dead by
now!).
I did not -- I measured 5V across it when the keyboard was plugged in,
that's all.
In some cases one of the 'wires' in the
housing that fits into a
pin socket on the light source assembly is acutally a resistor.
The encoder disk comes out by springing the circlip off the spindle
(outside the encoder, on the knob end of the fixing bush) and sliding the
spindle/disk out backawards. Inside the housign is the detector module
with a little slotted metal grating on top.
Repairing this is not easy. When a similar enocder in an Olivettie JP101
Sparkjet printer died, I fixed it using the sensor from an optomechanical
mouse (such things were easy to find back then...)( and a bit of simple
circuitry (I think a 74LS14). I think, though, that opto-mechncial shaft
encorders as used in these HP keyboards are still available, if not
exactly cheap. if it has failed, it may be simplest to just replace it.
But first, does it do anything at all?
Thanks for the tips -- I'll do some fooling with it this week (once I
clear off some workbench space again) and let you know.
Thanks,
Josh
-tony