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.

HOW DOES IT WORK?.....

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 )