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The Project 64 etext of ~Changing a 1541 from Device 8~, by Ray
Carlsen <rrcc@u.washington.edu>.

DUAL10.TXT, July 1997, etext #264#

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CHANGING A 1541 FROM DEVICE 8 TO DEVICE 9, 10, or 11
(also included: SX-64 and 1571D device select info)

Latest additions & corrections: 06-22-97

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.
This is a hardware modification that permanently sets the drive to a
different device number unless changed back to the factory setting.

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 are part of the "foils" or printed circuit
traces on top of the board inside the drive. The foil pad jumpers
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 IC3, a
6522 VIA. 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).

The built-in drive in the SX-64 is a 1541 with the ALPS mechanism.
(That is the only one I've seen installed.) The controller (called the
FDD board) for that drive is PCB# 251109. It has two jumpers, like the
stand-alone drives, for drive selection. They are located between plug
P19 and plug P22 (which goes to the drive reset switch). Jumper #1 is
the one closest to P19. I wired my own SX with a four position slide
switch on the left rear side of the unit to be able to set the number
from 8 to 11. The SX is very compact and hard to work on. The
modification to add the switch should really be done by a tech.

The 1541-II, like the 1571 and 1581, was built with two tiny
paddle-switches on the rear of the drive to select the device number.
Interestingly enough, the internal 1571 in the C-128D has no external
switches for drive select... it is factory set for device #8. There
are drive select jumpers inside the 128D, however, on the motherboard
near the drive. If you look at the PC board just under the left side
of the drive, you will see them. It is not necessary to remove the
drive unless you plan to solder in there. The jumpers are located near
U106 (a 6522), U114 and U112. DS jumper #1 is nearest to U112, towards
the front of the computer.

Ray Carlsen
CARLSEN ELECTRONICS

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End of the Project 64 etext of Changing a 1541 from Device 8.

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