CHANGING A 1541 FROM DEVICE 8 TO DEVICE 9, 10, or 11

             Latest additions & corrections: 9-11-13

     There were at least three versions of the 1541, each with a 
different PC board, and two types of drive mechanisms. The following is 
the procedure for modifying a 1541 to enable a different device number.
     All drives were shipped from the factory as device #8, with no
jumpers cut. The jumpers, by the way, are two tiny silver half-circles
with a "dash" in the center. They resemble a fat letter H. To open a
jumper, cut the dash with a sharp knife. If you accidently cut the wrong
one, you can apply a blob of solder to re-connect the two half-circles, or
just lay a small bit of wire across it and solder it. Don't heat it for
more than a few seconds or you will lift the trace off the board. Jumpers
are usually marked 1 (or A) and 2 (or B). To change the device number from
the factory setting of #8 to device #9, cut the jumper marked 1 or A. For
device 10, cut the one marked 2 or B. If you cut both jumpers, you have
device 11. These two jumpers represent grounds going to a 6522 VIA chip. 
Jumper 1 (or A) is pin 15 of the chip, and 2 (or B) is pin 16. You can
remove that IC, lift one or both pins, then re-insert it into it's socket
to change the device number (for example, lift pin 15 for device #9) but
it is best to cut the proper jumper... the chip pins will break off if
bent more than a few times. 
     By installing a device 8/9 switch (a SPST toggle switch that opens
and closes jumper #1), you can easily switch back and forth between drive
8 and 9 without opening the drive. Each terminal of the added switch is
wired to one side of the cut jumper. The solder pads are so tiny that,
unless you are proficient with a soldering iron, it is best to leave that
work to a technician. Obviously, the modification should only be done with
the drive turned off and all plugs disconnected. The most convenient place
to mount the switch is on the front right-hand side of the drive. The
spacing is tight behind the front panel... make sure you drill the hole
with enough room behind it for the body of the switch. Solder the wires to
the switch before you mount it... it's easier. 
     Facing the front of the drive with the case top and shield removed,
the drive select jumpers are located as follows for the various models: 
The early VIC-1541 (sometimes called the 1540) in the white case had the
long board and used the ALPS drive mechanism with the push-down door. The
drive select jumpers, marked 1 and 2, were near the rear of the board,
right next to the 6522 chip UAB1. Cut jumper 1 for device #9, jumper 2 for
device #10, and both for 11.
     Next came the shorter board 1541 in the standard brown case. It used
the ALPS (push-down) mechanism and a silver colored metal shield. The PC
board number was 1540050. Some of those board's drive select jumpers were
marked A and B, some 1 and 2, and some were unmarked.  The jumpers were
located 2" from the front of the board and 2 1/4" from the left side. They
are positioned between electrolytic capacitor C46 and transistor Q3. 
Jumper 1 (or A)  would be closest to the transistor.  Again, cut 1 or A
for device #9, etc. as above.
     A later version 1541 (sometimes called the 1542) had a shorter board
(PCB #251830 or 251777), and used the Newtronics drive exclusively. The
metal shield was gold in color. This drive was apparently the most common.
Drive select jumpers are 1.5" from the front of the board and 2" from the
left side. The jumper pads marked 1 and 2 are between transistors Q4 and
Q5. Jumper #1 is closest to transistor Q5.
     The latest version was the 1541C (PCB# 251854) and used the
Newtronics mechanism in a off-white case. That's the only one with the
photo-sensor to detect track zero, but it was disabled by Commodore, so
the drive head still bangs like the earlier drives. The drive select
jumpers are called J1 and J2, and are located 1 3/4" from the front of the
board and 1/2" from the left side (near plug P1).