View Full Version : Multiple Commodore 1541 Disk Drives

Postal Patron
March 14th, 2004, 06:48 PM
I'd like to have more than one 1541 drive attached, but there is a hardware mod mentioned on Ch 9 page 40 of the 1541 Disk Drive book where it is mentioned that there is two jumpers that both or either have to be cut to make it a physically seperate drive. For instance, a "load '*',8,1" would provide a dir on drive 1, so cutting the first jumper would add 1 to the 8 (load '*',9,1), cutting the second jumper would add 2 to the 8 (load "*",10,1), and both would add three for a new command.

The Disk Drive book does not specify where the jumpers are. It just says, facing the front, it is in the left middle of the board, no interface number or pic or anything. Since the Commodore 1541 Disk Drive book is the authority on the planet for this piece of hardware, is there somewhere else which describes the exact loation of the jumpers and is there a way to make a non-permanant fix?

March 14th, 2004, 07:38 PM
I'd have to find and pull apart one of my C= drives to see what the board looks like. I'm pretty sure it would be fairly obvious what the jumpers look like. I'm not sure that any of my drives are out of storage at the moment.

The best solution, if you plan on changing the drive ID frequently, is to install a switch or switch package to either side of the jumper.

Good luck!


Terry Yager
March 14th, 2004, 08:40 PM
The jumpers are just about in the middle of the circuit board, a little towards the front, and just a tad off to the left (as viewed from the front). They look sum'n like this (excuse my poor attempt at ASCII art):


Where the 0s represent the solder pads and the -s are the traces that must be cut. And yes, some people have been known to install switches (accessable from the outside) to change the selects. It's not hard to figger out how, once you look at the setup inside.


Postal Patron
March 15th, 2004, 02:31 PM

Could someone point exactly where it is? Sorry, I don't want to cut the wrong wire. I marked the possible locations with letters A-I. If I'm of base, let me know, and I'll reletter. Thanks

March 15th, 2004, 02:47 PM
The picture doesn't show up here because GeoCities isn't all that nice about linking in.

You can cut and paste the URL (http://www.geocities.com/srm806/dd.jpg)to the picture into a browser window to see it.

I couldn't find the drive select area in the picture but I can say for sure that it's not A through F.

I found this: http://home.att.net/~rmestel/articles/drive8_9.txt that might help a bit:

Painless 8/9 Drive Select

I have discovered an interesting method of adding unit eight/nine selection to a 1541. My technique
does not require any external switches, only a single two inch wire inside the case.

1. Open up the drive and expose the main printed circuit board. If you don't know how to do this, then
you probably shouldn't be trying this modification.

2 Cut the PCB jumper labeled El. There are two of these. El and E2. El is nearer the front. They are
about a quarter inch in diameter, and are close to the center of the board about two inches back from
the front edge. There is a thin strip of metal connecting the two halves. Carefully cut it with a sharp
knife. Reconnect the drive to the computer, put in a disk and see if you can LOAD "$",9. If the drive
comes to life, then the jumper has been completely cut.

3 Now carefully solder a two inch wire to the right hand half circle of El.

4. Next find R44. This is a l00 K resistor (brown, black, yellow) between UD1 (a 7406) and UD2 (a
7417). These are near the long connector on the left edge of the board. Solder the other end of the
two inch wire to the end of R44 nearest the front of the drive.

5 You're done. Put it back together. Easy wasn't it?

Connect the drive to the computer and with no disk in the drive, turn on the 1541. You should be able
to use it normally as good old unit eight. Now turn the drive off, insert a disk half way, and turn it back
on. You will find the unit now is number nine.


You have just wired the disk controller address option pad to the write protect sensor. Since the 1541
reads these option pads on power up, if you have the write protect sensor blocked when you turn it on,
the drive becomes a nine. If there is no disk or a non-write protected disk in the drive, it will be unit
eight Sure beats boring holes in the case.

Jim Harvey, 18538 Inkster, Redford, MI 48240

(Reprinted from Tri-City Commodore Club newsletter February 1997, via the Commodore
Information Center http://home.att.net/~rmestel/commodore.html )

I'll see if I can find something else later. . .

Good luck!


vic user
March 15th, 2004, 03:59 PM
Ray Carlsen's site may be of use to you:



March 16th, 2004, 05:09 AM
The only two H-shaped silver jumpers where you can cut are about one inch to the right of "F" in the mentioned picture. I haven't done it myself, so I wouldn't know, but it seems reasonable.

I wonder if the device number change depending on the write protect sensor will survive a soft reset when the drive spins up. Logically it would check for write protect on every reboot, so if you have forced it into unit 9 but then leave a disk completely inside, maybe it will become 8 if that disk is not write protected?

Postal Patron
March 22nd, 2004, 05:56 PM
I redid the pic to circle the two jumpers to cut. I was thinking of a physical wire, but it was a bare solder connection. Thanks to all, you all helped in my understanding. Too bad you have to open your case and cut it like this. In my limited testing, much C64 software is hardcoded to read the first drive (device 8). When I tried using software in device 10, there were hard reads to device 8. Oh well. I just want a mechanism to easily backup disks, instead of tediously going thru disk copies with one drive (Ugh!)

Feel free to use the pic as a teaching aid.

Kaptain Skitzo
December 12th, 2004, 09:52 AM
I realize that it sounds like a major chore to do it, but it's actually very easy.

there are 4 screws on the case to remove, and 2 or 3 on the mesh cage covering the circuit board. Once you locate the jumpers as shown on the picture above(various revisions on the board put them in different places, but on the stand alone drives, there is only 1 set of them).

Simply cut through the jumper with an exacto-knife or razor blade. I've done this dozens of times, and a small drop of solder will reverse the procedure.

With an SX-64, there are 2 sets of those jumpers on the Drive's controller board. I've done that(due to the internal drive not reading anything).
That's a major operation, and not for the feignt of heart.

Terry Yager
December 12th, 2004, 07:25 PM
The picture above shows the right jumpers circled. If you cut the one farthest to the rear, it becomes device #9. Cutting the front one makes it a device #10, and cutting both jumpers produces device #11, IIRC.


Kaptain Skitzo
December 13th, 2004, 08:14 AM
You remember correctly. I wasn't sure offhand, until I happened to look at the board in one of mine.