DISK II DRIVE: Which "daughterboard" IC's control speed?

[sebugg@presby.edu (Stephen Buggie)]

                DISK II CLONE DRIVE: BACK PANEL DAUGHTER-BOARD:
                     WHICH ICs CONTROL THE DRIVE SPEED?
                ==============================================


       Yesterday, I advertised four "Disk II clone" drives for sale in
working order.  I decided to check them out again, and must amend the
ad to state that THREE are in working order.  One of them, salvaged from
a Franklin Ace 1200, just spins and spins.

       Using Master Diagnostics IIe, I determined that the speed in the
wayward drive is much too fast.  Yes, I know about the set-screw speed
located on the rear-panel daughterboard.  Adjusting that set screw had no
effect on speed; the indicator remained pinned at the fast maximum indi-
cator point.

       Next, using the identical twin Franklin clone drive, I
systematicaly swapped the 8 ICs from the bad to good analog card.  All
eight ICs were good.  Next, I swapped the entire analog card; it too is
good.   Next, I swapped the 20-line ribbon cable; it too is good.

       Therefore, I deduce that the fault is in the back-panel
"daughterboard" of the Disk II clone.  Thus who have tickered with
their Disk II drives --- or merely peeked inside --- can visualize the
board I am writing about.  It is a small circuit board near the back of
the Disk II clone.  This one has four ICs on it.   It is the board on
which is mounted the speed-adjuster set-screw.

       None of the ICs or other components on the back-panel daughterboard
looks "cooked" or otherwise damaged.  All the parts are soldered to the
daughterboard, so they will be hard to replace.

       HARDWARE HACKERS ARE ASKED TO ADVISE which of the following
components ought to be given highest priority in testing since I will
replace them, one component at a time.  Again, externally none appear
to be damaged in any way.

SPEED ADJUSTER SET-SCREW.    (3 pins soldered to board)

IC:  CA 339

IC: 74LS123

IC: 74LS05

POWER TRANSISTOR (3 pins, large):  TIP 110   236

The 3 ICs have 14 or 16 pins.  When I replace them on the daughterboard,
the plan is to install sockets so the ICs will be inserted into the
sockets.

Hardware experts, please send your recommendations!  Tell which of the
above components, when failed, will result in a high drive speed that
does not respond to adjustment of the speed set-screw.

Stephen               sebugg@presby.edu




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 ** Stephen Buggie  Psych Dept  Presbyterian College   Clinton SC 29325 **
 ** sebugg@presby.edu                 voice: (803) 833-8337 or 833-1632 **
 **            On internet my 65c02 masquerades as a Pentium            **
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