MSD-SD2 schematic, service information and operators manual on 7-6-05.

           MSD-SD2 schematic, service information and operators manual on 7-6-05

Look for the MSD-SD2 schematic, service information and operators manual on 
my schematics website:

Quoting from the operators manual, except for my additions for clarity:


     The device number on the MSD SUPER DISK DRIVE (dual: SD2) comes from 
the factory selected as device number 8, drive number 0 and 1. This is the 
usual or "default" device number, but if more than one disk drive is to be 
used with the system, it is necessary to give each disk drive a different 
device number or drive number. With this disk drive, it is not possible to 
change the drive numbers (ie 0 and 1), but the device number can be changed 
using either software (a short BASIC program after power up) or hardware 
(changing jumpers on the drive PC board). 
     The disk drive determines its device number from a set of jumpers on 
the PC board inside the drive. At the time the drive is powered on, the 
jumper settings are "read" by the microprocessor and the resulting number 
is stored in a specific memory location. This makes it possible to change 
the default device number by changing (opening or closing) the jumpers. 
After power up, the device number can be changed by using a "memory-write"
command to the memory location that has the device number stored in it. 
That command must be used each time the drive is turned on. Each method has 
advantages and disadvantages which will be detailed below. 


1. Turn off the drive and remove all cables from the drive.
2. Remove six screws from the drive case and remove the top cover. 
3. Locate the jumper block JB1 on the top of the PC board near the rear of 
the drive. It is located between ICs U10 and U11. At that location, there 
are four solder pads with two bare wire "jumpers" soldered in horizontally. 
This is the factory configuration for device 8. If JB1-1 is cut (or simply 
unplugged if a "header" with a removable jumper is installed), the drive 
will respond as device 9 when powered up. If the jumper at JB1-2 is removed, 
the drive will be device 10, and with both jumpers removed, device 11. A 
SPST (single pole, single pole) switch can be installed instead of a jumper 
to allow the drive to be changed later without opening the case. Note: 
there is room on the rear of the case for added switches.
4. Replace the case top and install the cabinet screws. 
     Electrically, the two jumpers ground two pins of an IC, namely U22 
buffer (74LS240) pins 11 and 17. With a jumper at JB1-1, pin 17 of U22 is 
grounded, and with a jumper at UB1-2, pin 11 is grounded. This info is 
helpful in case the solder pads or board traces become damaged and cannot 
be used.


     The device number can be changed by performing a memory-write to 
locations $0077 and $0078. The memory-write command is performed after the 
command channel has been opened with a BASIC statement, usually:
OPEN 15,8,15 
The memory-write has the following format:
The dv represents the device number that is desired. An example routine for 
changing the drive from device 8 to device 9 is:
10 OPEN 15,8,15
20 PRINT#15,"M-W"CHR$(119)CHR$(0)CHR$(2)CHR$(9+32)CHR$(9+64)
30 CLOSE 15
To make it easier, this little program can be written to a disk and run each 
time the number change is needed rather than typing it out every time. The 
program can be written all on one line by using a colon between statements.
     It is usually desirable to change the device number in hardware unless 
a temporary change is all that is needed. In order to use the software method, 
only one drive can be powered on, its device number changed, then the next 
drive powered on and its device number changed, until all drives are on. If 
this procedure is not followed, there will be a device "conflict" on the 
serial bus and the drives will not work reliably or at all. 


     In my SD2, the PC board tends to bow outward physically towards the 
metal case. I didn't want a short circuit to damage the drive, so I installed 
a 6" X 6" cardboard spacer to keep the board away from the case top. A sheet 
of thick plastic glued to the inside of the case top would work as well. 
     The original cabinet screws were missing when I got my SD2. I noticed 
that if the replacement screws were any longer than about 1/4", they would 
hit the PC board inside. The important ones are the three on the side of 
the case away from the drive mechanisms and closest to the PC board inside. 

ERROR FLASH CODES FOR THE SD2 (seen at power up if there is a fault)

Number of flashes  Suspected component failure
1		   Micro U7
2		   RAM U1
3		   RAM U2
4		   RAM U3
5		   ROM U5
6		   ROM U6
7		   Drive mechanism

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