WIRING HARNESS SOLUTION
by John Alwood, RKUG, July 1987

(A look at a wiring harness problem in early Kaypros)

THE PROBLEM:  You are sitting at your computer and you notice
that any of the following events happen at irregular intervals: 
(1) one disk drive starts up under its own initiative -- without
the benefit of control from the program you may be using at the
time; (2) both disk drives light up, but they may not actually
begin moving (ie, rotating and moving the read heads) and they
may actually "lock up" and force you to re-boot before you can
save anything; and/or (3) your entire system locks up and you
must reboot to regain control.  In the later stages of the
problem, even a "reboot" won't solve the problem.  Sometimes,
powering the computer off and on will work.  Eventually, the
machine will not work at all.  The problem may seem heat-related
because it usually only happens after the computer has been
running for awhile.

THE DIAGNOSIS:  The problem is heat-related.  It is also
"vibration" related.  And, most of all, it is "solder" related. 
One of the solder joints on the power supply board connecting the
wiring harness to the board has"expanded" and has caused the pin
to lose contact with the power supply board (there are about 9 or
10 pins in this wiring harness).  As a result, your computer
loses its power source -- either the A/C voltage from the power
line is not making it into the power supply circuits, or the DC
voltage from the power supply board is not making it over to the
main CPU board and disk drives.

Due to the "heat" expansion at the location of the defective
solder joint, your computer effectively loses power and "locks
up".  Vibrations (such as banging on the top of your computer)
may either cause the joint to regain contact -- or it might cause
a functioning joint to lose contact.  Installing a fan inside the
computer will (to a limited extent) solve the heat problem.  But
it will do nothing to prevent "vibrations from causing the joint
at the defective solder joint to break the electrical connection.

THE SOLUTION:  Remove the power supply board and resolder the
wiring-harness pins to the power supply board.  The problem was
caused by sub-standard manufacturing processes by whomever
produced the Kaypro CP/M power supply boards.  Most of the other
components on the power supply board received ample solder,
sufficient enough to ensure a permanent bond.  However, since the
pins in the wiring-harness that distribute electrical power to
the rest of the computer are "thicker" than other component
connections, they require more solder to hold them to the board.

In order to make up for this deficiency, you merely need to add
more solder to that already present at these joints.  Anyone who
has any experience with a soldering iron can do this -- no
computer chips are involved, no "small" or "sensitive" components
are involved, and it would be difficult (but not impossible) for
you to damage the power supply board when you are adding solder
to the wiring-harness joints.  It took me only 60 seconds to
complete the soldering.  The problem has completely disappeared! 
As a result, I don't need to spend between $2,000 and $4,000 for
a new computer (at least not right now, anyway!).  If I need MS-
DOS for anything, I will use my "work" computer.  My CP/M Kaypro
will continue to be my primary "home" computer.  And for a few
weeks, I was actually beginning to believe that CP/M was dead!  I
was getting ready to bury it when I figured out how to bring it
back to life.

For additional information concerning this CP/M Kaypro power
supply problem, see the May 1987 PROFILES, page 69 and the Nov-
Dec 1986 (Vol 4 No 6) Kugram, pages 6-7.  I would strongly
recommend that anyone who is having "strange" problems with their
CP/M Kaypro should go ahead and resolder the power supply
wiring-harness joints before they start looking for the problem
elsewhere.
