jbh@mb2c.UUCP (02/22/87)
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 E1. There are two of these, E1 and E2, E1
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 E1.
4. Next find R44. This is a 100K 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.
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 only 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 Mich. 48240hedley@cbmvax.UUCP (02/22/87)
In article <2221@mb2c.UUCP> jbh@mb2c.UUCP writes: >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. > .... >You have just wired the disk controller address option pad to the write protect >sensor. ....... > Damn clever. I wish I'd thought of it. Hedley
abd@well.UUCP (02/24/87)
In article <2221@mb2c.UUCP> jbh@mb2c.UUCP writes: >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. > .... >You have just wired the disk controller address option pad to the write prot ect >sensor. ....... Unfortunately, this method will default to drive 9 if a read-only disk is fully inserted when a drive reset occurs. This will make it unusable with some commercial copy-protected games which require a drive 8 and which apparently reset the drive as part of their scheme. The proposed modification will make it impossible to use this software with the drive....
oronquil@megatest.UUCP (02/26/87)
In article <2636@well.UUCP> abd@well.UUCP (AbdulRahman Dennis Lomax) writes: >In article <2221@mb2c.UUCP> jbh@mb2c.UUCP writes: >>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. >> .... >>You have just wired the disk controller address option pad to the write prot >ect >>sensor. ....... > >Unfortunately, this method will default to drive 9 if a read-only disk >is fully inserted when a drive reset occurs. This will make it unusable >with some commercial copy-protected games which require a drive 8 and >which apparently reset the drive as part of their scheme. The proposed >modification will make it impossible to use this software with the >drive.... Then turn on the drive without a disk.
astrix@puff.UUCP (02/27/87)
Having a switch is nice if you have a lot of use for 8 & 9 on one drive, doing rewiring of the jumper is clever... But... don't forget that once the machine is on the address (8, 9, etc.) is settable by software too. Having only one drive, I've never had this "problem". Interesting variations! astrix (Lou R. Goodman), UW Madison ------------------------------------------------------------------- || He who knows, who really knows, and knows that he knows...... || || knows just how much he doesn't know...... || ------------------------------------------------------------------- || "Sticks and stones can break my bones, but flames... oy weh!" || -------------------------------------------------------------------
daemon@rutgers.UUCP (03/02/87)
From: prindle@NADC The point is that the jumpers are sensed whenever you turn the drive on *OR* whenever the drive is sent the "UJ" (power-on reset) command - the DOS cannot distinguish between these two since the UJ command executes exactly the same vector as a hardware reset (as in power-up or if a C64 is fitted with an external reset switch). Much commercial software does a "UJ" command as part of it's initialization so that it will not fail to load if a previous program has modified the drive RAM. If the software does this, the drive number will be reset to 8 (if the diskette in the drive at that moment is not protected), or 9 (if it is). You cannot remove the disk because, within a second, the software will attempt to perform a disk operation and encounter an error. While the internal mod to the 1541 is indeed clever, one must watch out for side effects such as this. Mounting a switch on the right front panel of the 1541 is still the most reliable method, and not particularly hard. Frank Prindle Prindle@NADC.arpa