MSD Single to Dual Transformation
                                  by
                              Lyle Giese 
                           DELPHI Mail: LYLEG


 
The subject of this article is something that I did several months
ago. I took my MSD SD-1 and converted it into dual drive. It was not
very hard to do and can be done with only a few parts. The most
expensive part of the deal is the disk drive itself. I have found only
two suppliers of them. Both of them advertise in the Computer Shopper.
The first is LDL Electronics in Jupiter, Fla. He advertises in the
classified section under disk drives.
 
The other is Lolir Lctronics. They usually have a big ad elsewhere in
the Computer Shopper. The units they had were used and in limited
supply.
 
I am sure that other suppliers can be found but the TEC FB501 disk
drive that MSD used is a Single Sided, Single Density drive. Almost
all of the ads you see for drives are for double sided and/or double
density drives. So they are not readily availible.
 
The MSD drive was engineered to be a dual drive (that is 2 units in one
case with one disk drive controller). When they made the single they
merely took out one of the drives and in some models took out one of
the 2k RAM chips.
 
The MSD when powering up tries to initialize both drives and if the
second is missing it goes into the single drive mode. One of the
differences you can see is the way the drive activity light works.
In the dual unit you have 3 leds. In the single there is only one led.
That single (the top one on the dual) led goes from green to red
whenever a file is open or when loading or saving data. On the dual
the power led is green and stays that way. The two other leds are one
for each of the drives and are off until you acess one of the drives
and then they behave like the red portion of the power led in single
mode.
 
The first thing you need to do is open up your single drive and look
at the memory chips in it. From the front on the top row are the
memory chips. MSD has places for four 2k RAM chips on the drive
controller board.
 
The first two memory chips are installed in all drives. The third is
needed for the dual only and the fourth one is not found in duals. In
some of the very early singles MSD populated all four memory chip
locations. If you have one of these singles (I did) you don't need to
add a memory chip. But if you need one they are a Synertek SY2128,
same as a National Semiconductor HM6116P-4.
 
Toward the back you will see two cables going from the controller
board to the disk drive. You have to parellel them both into the new
drive and with the third RAM chip in place you are actually done and
have a dual unit.
 
The ribbon cable sends and receives the signals from the controller to
the drive. Telling the drive to move the head if needed and taking and
sending the signals from the heads containing the actual data. The
drive also tells the controller over the cable if there is a disk in
the unit and if the disk has the write protect on or off. The
controller must also tell which drive it wants to talk to in the dual
unit.
 
The other cable carries the power needed to run the drive, 5 volts DC
to power the electronics on the drive and 12 volts DC to turn the
motors on the drive.
 
I purchased my drive from LDL in Jupiter, Fla. He was able to sell me
a short piece of ribbon cable and the necessary connectors. For
the power cable he has a small Y-power kit that will take the one
power connector and turn it into two for you.
 
The connectors that LDL sold me to tie the two cables together were
called an LDE male ribbon connector and a LDE female ribbon connector.
They contain two rows of pins to interconnect (34 in all). On the other
end of your new piece of ribbon cable, you put a card edge connector
to attach to the disk drive.
 
The hardest part of the whole conversion is putting the connectors on
the ribbon cable. I found that the vise mounted on my work bench
worked fine. However I would caution that you do not apply too much
tension with a vise as you could crush the connectors.
 
It is easy to get the connectors on the new piece of ribbon cable.
Putting the one on the existing cable is not as easy because it is
hard to do while the cable is connected to the controller card. MSD
used what is called a solder transition connector. The cable is not
removable from the controller card.
 
In order to get the connector on that piece of cable, it takes about
four hands and a little patience. Someone needs to hold the controller
cable close to the vise while holding on to the connector, all the
while keeping the ribbon cable straight inside the connector WHILE
tightening the vise down!
 
WHEW! Like I said it takes more than one pair of hands in this phase
of the project.
 
Now you can hook up the new drive and see if it works. But before you
power up the new drive, you have to change the drive number on the
unit. Near the rear of the drive, you will find an option plug. The
orignal drive will be set for drive 0. Move the option plug on the
second drive to 1.
 
On the orignal drive you must remove the terminator resistor pack.
They are hold up resistors and terminate the data lines. You only want
one set in the system and it should be on the last drive, in this case
the new drive. The resistor pack is at the rear of the drive and is in
an IC socket, designated RA11. All of the ICs on the drive are
soldered in so it will be easy to see it. Carefully remove the
resistor pack on drive 0 (your orignal one).
 
On the surface that will complete the project and after you plug in
the two cables, it should work at this point. But it should be pointed
out that some minor modifications to the new drive are needed in order
to read the GCR format, that CBM uses, reliably. The drives were made
for MFM (which is a different manner of recording the information on
the diskette that is used by IBM). Also you will want to add two leds.
 
It is easy to see the difference when you look at the printed circuit
boards on the two drives. The drive comes with 1/8 watt resistors
installed from the factory. The modification involves changing/adding
3 resistors. MSD used 1/4 watt resistors for the modification. The
difference in size of the resistors makes them very easy to spot on the
printed circuit board.
 
Resistor R9 is replaced with a 560 ohm resistor. Resistor R15 is
parrelled with a 56K ohm resistor. And R22 is changed to a 10K ohm
resistor. Be sure to use 1/4 watt or 1/8 watt resistors, not that
performance will change but you will have troule with bigger sized
resistors.

Again you might try and run your new drive without changing the
resistors and see if it will work well, before going to the trouble of
changing resistors. As was stated it is just to make the drive read
the GCR format better.
 
After you do that, you will want to add the two leds needed to show
drive activity and errors for each drive unit. Just under the green
led will be a place for two more leds. Most any led will work as long
as you don't reverse the leads. The voltage will not damage the unit
if you do reverse it, it just won't light up.
 
All that remains is to house your new dual drive in a new case and you
will be all set. I went to MSD directly and purchased their drive
cabinet from them. They insist on sending it out UPS COD. The total
cost of parts was about $140.00, but I think the price of the disk
drive has dropped a little since I bought mine.
 
Was it worth it? YES! It is wonderful to be able to copy a
diskette (that does not have any read errors) in under 2 minutes. And
that includes formatting the destination diskette! Being able to copy
files from one diskette to another without loading it into the
computer first (VERY time consuming!). It does take longer to transfer
a meduim size file than to copy a whole diskette. But it is very handy
when sorting files and certainly is faster than pulling the file into
the 64 and sending it out again.
 
That takes care of converting your single MSD. If you have any
questions you can contact me on the Flagship Forum or D-Mail via my
username LYLEG.
 
Enjoy and have fun with your new dual drive!