14 Jan
2009
14 Jan
'09
10:19 a.m.
Dear Fellow Enthusiasts ...
Firstly, I must admit to being somewhat of a 'lurker' here reading
with great interest the postings and never failing to be amazed at the
shear amount of amassed knowledge on the subject. My thanks to you all.
Is there anyone here that can help me with a Commodore Pet problem
that is really starting bug me !!
IO am not really a PET person, although I have repaired the odd one in
the past. But I might have some suggestions.
It is a Pet 2001 32N with a Computhink Pet II Disk Controller Board
and a pair of Dual Computhink drives (Model : DKH 642-I).
Question : Do these drives have their own PSU, or do they somehow draw DC
power from the PET? I am wondering if the extra load of the drive motors
turning on could e pullign a supply line low or something.
The machine starts up just fine and you can enter
DISKMON by typing
SYS11*4096
However, upon entering commands like $LOD,1,"FOO" the screen turns to
a complete screen full of small squares - chequer board style. Upon the
command $DIR,1 the screen briefly displays a boarder around the screen
where the directory content would normally appear and as soon as the
drive activates the screen turns to chequer board.
I have done the usual of re-seating the IC's, and I am hoping this
isn't failed ROM.
It might, alas, be a failed ROM (does anyone have a dump of this?). PETs
are, hopwever, notorious for failed IC sockets that cause all sorts of
'intereting' prolems. I'd replace the lot with good turned-pin ones. It
might not help, but it'll take one worry away.
Another clue maybe that for some reason, when the drives are
activated, BOTH drives activate together, which obviously they shouldnt.
Do you hacw scheamtics? How are the drives selected? Could both turnign on
together be a software problem (e.g. one it of an output port controls
each drive, so if software writes a value to that prot that asserts oth
bits then both drives turn on)? Or does this indicate a hardware problem
with the drive select logic?
-tony