Jules Richardson wrote:
I'd quite like to see those documented somewhere -
not just for CBM
machines, but in the context of any system. I bet there were all sorts
of oddball copy protection schemes around, and it'd be interesting to
see details of some of them scribbled down (as you've just done so
nicely!)
I distinctly remember that there was a book on how to program the 1541
in order to do exactly this, and had lots of examples. I unfortunately
never owned it. I found it, at the time, in of all places, the Queens
Public Library. I tried to re-check it out several times, but the
Library wouldn't let me hold it any longer than about 2 cycles. :-)
It had lots of code examples and such as to how to call the various
track and sector format routines, so you could seek to a specific track
(or half track) and then write the wrong track ID, or the wrong sector
for example.
I believe it was written by one of the guys that made one of the fancy
copiers. Perhaps qcopy (not sure of the name) or the Basement Boys...
wish I could remember the name of the book. :-(
There's some stuff here: "
http://rittwage.com/c64pp/dp.php?pg=protection " and "
http://www.tkk.fi/Misc/cbm/docs/ " about these topics. There's also some
interesting stuff here: "
http://www.geocities.com/profdredd/cprogram/cprogram.html "
I remember playing with the code in this book and forcing the 1541 to
seek past track #45. When you did this, the 1541 would emit a loud
clunk and then your drive head would be stuck. You'd have to take the
1541 apart and move the head manually.
It might have been that same book or another, but it had info as to how
to tweak the motor speed of the 1541 with a fluorescent light. The
motor had lines on it which would appear to be stopped under the light
of a fluorescent source at either 50 or 60Hz. (There were two rings of
lines, one for US, and one for Europe.) There was also a pot on the
1541 board that you could tweak to control the motor speed.
Another thing I ran into with the 1541 was that a (diode) bridge
commonly blew out. The symptom of this was that the power LED would
flicker at 30Hz when this happened. I couldn't find the right bridge at
my local Rat Shack at the time, so after figuring out which of the 4
diodes in the bridge died, I found a large diode and soldered it to the
pins of the bridge.) That bridge was a single component, not 4 diodes,
but it was an easy repair. The diode wasn't quite right, so it didn't
last very long, but it was a very easy repair, so I just repeated it. :-)
A few other tricks at the time, it was possible to get stereo sound out
of both the C128 and the C64 by taking another SID chip (these were
expensive at the time ~$30-$50), and bend a couple of the pins. One was
an address pin, the other was the sound out pin. You could then place
the new SID chip right smack ontop of the existing one (piggy-back),
solder a wire to the sound out pin and you got stereo.
Another trick was if you had a tape drive, you could use it as a very
crappy 1 bit audio digitizer. This didn't work all that well, but it
was something. Later someone wrote an article (in RUN Magazine
perhaps?) about getting a serial A->D converter. Was a little 8 pin
chip that you could attach to the CIA's shift register to read the
values off.
Another trick was that if you had the Pet Emulator (which wasn't a real
emulator, it just reshuffled video memory around to match the 4032's
memory map for video), and attached a small speaker to one of the pins
of the CIA which was the shift register output (I think this might have
been like CB1 or CB2 or something like that), you could also get Pet
like sound, but you'd have the change the poke addresses around to match
the CIA's. Was useful for all those old Pet games. :-)