EXCHANGE THE DRIVE IN THE SX64 WITH A STAND-ALONE 1541 MECHANISM 9-22-04.


           REPLACING THE DRIVE IN THE COMMODORE SX WITH A STAND-ALONE 1541 MECHANISM

           latest additions and/or corrections 9-22-04


> I want to swap the drive from my SX64 and a 1541 stand alone.
> When I took the drive out of the 1541 it had three white wire
> connectors and one black. On the SX all the wires go into one white
> connector and one black. What is the best way to fix this small
> problem?

     Simple question, complicated answer. ;-) It will take a bit of work to
fit that replacement drive because the connectors -are- different although
the drives themselves are essentially the same. Fortunately, the color
coding of the wires is the same (with some exceptions, discussed later).
Swapping a stand-alone drive mechanism into an SX involves changing the
three connectors on that drive into one 15 pin plug that fits the FDD board
connector. You can use the existing 15 pin plug from either drive as your
replacement (see precautions later in this article). The black plug is for 
the read/write head and it needs to be lengthened to reach the connector 
on the PC board. You can cut the one from the old drive and splice it 
onto the existing one when that plug is cut off. The four wires inside 
the shield are color coded and must be spliced and insulated from each 
other and from any metal around them. Note that one pin (2) on that black 
plug is not used and thay provides a "key" for proper orientation. The 
"missing" socket pin should line up with the "missing" wire in the plug. 
     If you carefully examine each white plug, you will see a number 1 on 
one end. That identifies pin 1 and is how you know which way to wire up 
and install the new plug. Mark each connector and board with a magic marker 
or felt tip pen to identify pin one before you start rewiring. Another 
important bit of information: the white plug on the SX and the white plug
on a stand alone drive look identical until you turn them over. Notice 
that the only way the replacement will fit on the SX connector is if it's
reversed!!! So, if you're going to use the plug from the stand-alone 
1541, all pins will have to be removed and refitted so that plug will fit 
the socket and each wire is oriented to the correct position. It would
be easier to just reuse the large white connector off the SX drive. 
     Although it's quite a bit of work, I would replace an SX drive if the 
existing one could not be easily repaired (bad R/W head, for example). 
I took my own SX and three different stand-alone drives apart to verify 
this information. That said, there are always unforseen problems with any 
first-time project. I don't usually make disclaimers but I feel I must in 
this case. Some of the wires are the same color, so it's easy to make a 
mistake when rewiring the connectors. That's why I always rewire plugs
one pin at a time. I make notes as I pull things apart and label each item.
      Rather than cut and solder, it's easiest to remove each wire from the
three white connectors by releasing them and pulling them out. The
retainers can be seen if you look closely at the openings in one side of
the connectors. Each pin has a tab on one side that needs to be pushed flat
with a pointed tool so the pin can be pulled out by tugging gently on the
wire. Don't use too much force or you'll bend the pins. To reinstall those
pins, the tab will have to be pulled back up a little so the pin will snap
into the new socket and not fall out. I prefer to use a small jewelers 
screwdriver (but a large straight pin works fine too) to help slide the 
pins out of the connectors. The same tool can be used to force the pins 
tabs back open by pushing the point of the pin into the void under the tab. 
Too much bending back and forth will break that tab, by the way... and the'
pin will not stay in the connector. If that happens, the pin will have to 
be replaced (another one soldered onto the wire). 
     You will run into a few problems if you try to install a Newtronics
drive in the SX. It will work, but there are mechanical differences between
the existing ALPS drive and the later Newtronics mechanisms that make it a
less than optimal match. Notice that the Newtronics twist-down door latch
sticks out about 3/8" further that the ALPS push-down door. The Newtronics
latch will hit the keys when the keyboard is fitted onto the front of the
computer for storage or transport, but it looks like there is enough
clearance. The only way to know for sure is to try it. A more difficult
problem with the Newtronics mechanism is the metal plates that stick out on
the sides of the case and prevent the SX mounting bracket from being easily
installed. Compare the drives side by side to see the difference. One fix
is to grind off the excess metal with a file (looks like a real grunt). If
you add shims or washers to make the drive fit the SX plate, it will be
difficult or impossible to remount that plate correctly in the computer.
Not all the screws will line up with the base underneath unless you redrill
the plate. Because of those problems, I would go for the ALPS drive as a
replacement. They are more reliable in an SX because they don't run as hot
as in a stand-alone 1541.
     You will need the pinouts of the two types of drives. Note that the
same wire colors are used more than once. That makes it necessary to trace
each one back and find out where it originates so you know each one is
re-wired correctly. To make tracing easier, you will probably want to cut
the wire ties and free the wires from the bundles. Be careful you don't
nick or cut any wires! Retie the wire bundles with string when you're
finished. Note: NC below means no connection.

1541 STAND-ALONE            SX 1541 INTERNAL DRIVE

P5 (SPINDLE MOTOR)          P21 (SINGLE WHITE CONNECTOR)
 1  BLACK, common            13
 2  BROWN, +12V              12
 3  ORANGE, motor on/off     11

P6 (SENSORS)
 1  YELLOW, wp ground        15 (note: the SX wire is blue)
 2  BROWN, wp LED +          14
 3  NC
 4  NC
 5  NC
 6  NC
 7  NC
 8  RED, activity LED anode  8
 9  BLK, activity LED cath   7
 10 NC
 11 NC
 12 ORANGE, wp sensor +      4
 13 GREEN, wp sensor ground  3
 14 NC
 15 NC

P7 (STEPPER MOTOR)
 1  RED, +12V                9
 2  RED, +12V                10
 3  YELLOW, step 2           6
 4  ORANGE, step 0           5
 5  BLACK, step 1            2
 6  BROWN, step 3            1


Ray Carlsen CET
Carlsen Electronics... a leader in trailing-edge technology.