Fairlight-CMI

I recently repaired my Series III pen.
The pen internals are not documented in the Series III Service 
Manual, so I had to do my own homework.  I thought I'd share what I 
discovered:


Tools Used:
- soldering iron with fine-point tip
- fine solder
- flux
- tweezers
- wire-stripper/clipper
- X-acto knife
- Super Glue

note:   PCB = printed circuit board


Disassembling The Pen:


-unscrew both endcaps at each end of the pen.
-remove the large endcap at the pen tip side.
-simply slide the endcap at the cable-side up towards the Preh 
keyboard
 and move it out of the way.
-gently push some of the black cable inside the pen tube to provide 
slack
 while you slowly pull the pen post and PCB assembly out of the pen 
tube.
-be careful of the pushbutton while doing this.  the pushbutton is 
spring-loaded
 and has a small black conductive disc attached to its underside.  
do not lose the
 small disc under the pushbutton.  I recommend you super-glue it to 
the bottom
 of the pushbutton so it doesn't come off during these maintenance 
procedures.
-with the pushbutton spring cleared, the complete pen PCB assembly
 can be slid out of the pen tube.
-at the cable side, there are 4 wires soldered to the pen PCB from 
the black cable
 sheath.
-holding the pen assembly horizontally with pin tip to the left, and 
cable to the right
 the wire attachment order is: White, Green, Brown, Ground.  The 
Yellow wire is not used.


Problem Areas To Look For:


- Dirty contact pads on the pen PCB where the push-button's 
conductive pad 
  makes contact when pressed in.  There are 2 exposed PCB pads 
surrounded by a clear
  plastic shield.  The shield protects and insulates the PCB from 
the spring under the
  pushbutton.  The little black disc makes contact with the PCB pads 
and closes the
  circuit when the pushbutton is pressed.  This makes a pen button-
press event occur.
  Clean the contact pads with an erasor tip of a pencil or a Q-tip 
with rubbing alcohol.
  Don't attempt to scratch the contact pads clean with a metal 
screwdriver or similar.
  
- Bad solder joints where the 4 wires are soldered to the pen PCB 
board.  The 4 wires
  are very fine braided-strand, and can become crimped or kinked 
where they solder to the PCB.
  After many years, they may only be hanging on by a few strands of 
the wire braid.
  Clip the wires or unsolder from the PCB and strip them with new 
ends.  Re-solder to PCB
  while maintaining the correct attachement order:  White, Green, 
Brown, Ground (Copper shield)
  From the factory, Fairlight ran the wires from the bottom side up 
through the via holes 
  in the PCB to the solder pads on the top of the PCB.  I simply 
soldered them directly to the top 
  pads in a flat horizontal position, thus avoiding the additonal 90-
degree angle stress point 
  by coming up underneath through the via holes that was causing the 
kinks in the first place.
  
- Pinched & broken wires inside the black cable at the bend/stress 
point where it enters
  the pen tube and is pinched by the endcap.  This is clearly an 
area where my pen had a problem.
  The black cable is pinched at this point.  The fine-braid wires 
inside the black sheath
  get pinched and develop faulty, intermittent breaks when moving 
the cable around.  In my
  case, I could see the cross-hairs on the VDU disappear and re-
appear when moving the black
  cable around near this stress point at the endcap.  You cut the 
whole black cable off at the bend,
  strip back 1 inch or so of black plastic sheath, strip the 4 wires 
and solder them to the pen
  PCB as described previously.  Works like a charm.  You only lose 
about 1-2 inches of total cable
  length, and there is plenty of slack left on the cable to use the 
pen normally.

- Insufficient contact pressure from the wipers to the pen post 
inside the silver tube
  assembly.  Mounted on the pen PCB board is a silver "tube", where 
the pen post enters and
  is met by a set of internal contact wipers inside the tube.  The 
contact wipers are inside the
  silver tube, but they are mounted to the PCB by 4 through-hole 
vias, which can be seen on the
  underside of the PCB.  By heating up the 4 vias with the soldering 
iron, you can adjust the
  angle of the wipers and improve their contact pressure on the pen 
post.  There is a view hole
  in the tube to see the wipers and the pen post orientation.


Running The CMI Keyboard & Pen Diagnostics Software:


- Exit to OS9 (don't just shell out from CMI, quit out completely to 
OS9)
- Press these 4 keys at the same time:     CTRL SHIFT REP DEL
- CMI keyboard/pen diag tool starts running
- Press each keyboard key to see the key name/type displayed on the 
VDU
- Move the pen around the tablet and press the pen button, see the 
pen X & Y coordinates
  on the tablet get displayed on the VDU.  When the pen button is 
pressed, the VDU shows
  ON for pen button-press event, and OFF when pen button is not 
pressed.
- You can test all your pen and keyboard functions with this tool to 
verify it is working
  properly.
- To exit the diag tool press these 4 keys again at the same time:  
CTRL SHIFT REP DEL



All of this worked like a charm, and my Series III pen is a happy 
camper.

cheers,
David Wilson