[net.micro.cbm] Commodore cassette problems

stottlem@ittral.UUCP (Bill Stottlemyer) (02/28/84)

I'm using the Commodore Datasette with my C-64 and encountering quite a
few load data errors. I'm using high quality cassettes (Microsette brand)
and I've cleaned and de-magnetized the tape heads with little or no
improvement in performance. I didn't have this much trouble with my
Sinclair ZX-81 using a standard audio cassette. Question: Could I
possibly have problems with tape head azimuth alignment. What about
problems in the tape drive path? Also, is there a standard reference
tape available for checking tape head alignment? Any suggestions short
of going back to the Sinclair would be greatly appreciated.
                                         
                                      Bill Stottlemyer

porter@inuxd.UUCP (J Porter) (03/01/84)

Look at the output from the cassette drive with a scope
when playing back a known good tape that you want to be
able to load.  Then with a small screwdriver, gently adjust
the azimuth (through the tiny hole in the top of the drive)
(If you have an older cassette unit, you will have to lift
up the nameplate).  Simply adjust for the best digital looking
signal.  The front of a program has seven seconds of pure tone
before data.  This portion should come out looking like a 
real clean square wave.  Happy Hacking.

Jeff Porter  (inuxd!porter)
AT&T Consumer Products
Indianapolis

miller@uiucdcs.UUCP (miller ) (03/02/84)

#R:ittral:-37300:uiucdcs:36100058:000:591
uiucdcs!miller    Mar  1 16:50:00 1984

     A friend of mine had a cassette and found it to be *very* sensitive to
the TV.  He had to move it far away or he got tons of load errors too.  This
may not be your problem, but if so it will save you a lot of unneeded hardware
debugging.
     Also on another note, be careful with that grounding wire on the cassette
line.  If it touches the wrong contact on your expansion or user port, you
potentially could fry part of the machine.  It is not used on the vic or c64,
only for Commodore's business machines.  So be sure you tape it down next to
the line.

A. Ray Miller
Univ Illinois

dollas@uiuccsb.UUCP (03/02/84)

#R:ittral:-37300:uiuccsb:16800009:000:1495
uiuccsb!dollas    Mar  1 11:50:00 1984

   One of the most significant factors is the interference from the TV/monitor
screen. Try to keep your datasette far from it (you can even put a metal
pan over it to see if this is indeed the problem -so much about technology); if
so just make longer cables and ...reach out!
   If you use a homebrew interface (I use one all the time) it might be 
sensitive to tone and volume levels. Usually once you've got the proper 
settings it works fine. In fact with my roomate's SANYO (no, I don't work
for them) and TDK SA cassettes  (Chromium setting - I don't work for TDK either)
we get virtually no loading errors even when the recorder is 1ft off 
of the TV!
   The azimuth may be a reason for problems but I would think that it would
give problems with both FSK (Sinclair) and PCM (Commodore) coding schemes. On
the other hand noise tolerance may be different, by adding noise with 
frequency components far beyond the ranges it looks for in FSK you may still
get good results whereas in PCM it might interpret this noise as transitions
thus goofing up.
   As a final comment you may get better results if you use magnetic 'donuts'
at the ends of each wire (that connects the interface to your datasette).

   Good Luck
                                                 Apostolos Dollas
                                                Dept. of Comp. Sci.
                                                     U. of Ill. 
                                         ...!pur-ee!uiucdcs!uiuccsb!dollas