3 Aug
2014
3 Aug
'14
5:10 p.m.
Tony & All,
I do have the factory service manual for the 1541, and it doesn't have any
info on signal waveforms / levels. I'm aware of some diffs between the 1541
and 'standard' drives, though once you get to the mechanism itself, much
generic info should apply. Most important thing to realize is that the 1541
& cousins are smart peripherals - essentially complete appliance-ized
computers with CPU, RAM, ROM, I/O & PSU all dedicated to serving a floppy
mechanism - so they are +much+ more complex than a basic 5-1/4" drive.
Both of the problem drives seem to have roughly the same problem - they
don't seem to be able to read anything at all, and the heads barely move.
One drive is in an SX-64, the other is an Enhancer 2000 3rd party unit.
As an example: Attempt to load a directory.. motor spins up, LED lights
then flickers as the drive does little else. Eventually a "FILE NOT FOUND"
error will pop out. The head never moves at all in some cases, in others,
it seems to toggle between two tracks or half-tracks, seemingly on or near
the directory track (18 of 35).
First guess was mech. problem with the head / stepper motor / rails etc,
but at least in the SX-64 I was able to swap mechanisms and the error
stayed with the machine. I then swapped FDD boards between the two SX-64s
and the problem followed the FDD board - so it's a board problem.
Next guess was bad servo drive signals, which go like PLA -> 7404 ->
ULN2064 (open-collector Darlington driver) -> step motor phases x 4. But
this all seems OK as well.. If I watch servo signals on both "good" and
"bad" drives as I send an unending string of commands (like I0:, which is
"initialize the drive hardware") I see the exact same signals with the same
co-incidence with head noises & drive actions on both drives.
So I took a closer look at Ray's repair guide, and here's what I see..
(more in the next post)
On Sun, Aug 3, 2014 at 3:06 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Greetings folks,
I've got a couple of dead C-1541 drives here, and not nearly enough
knowledge / info to troubleshoot them.
I hve no idea if these are on-line anywhere (I have them on paper), but
there is an official Commodor service manual for the 1541. It's just
scheamtics and parts lists.
More use to you, if you can find it is the SAMS troubleshooting guide.
This (might) be on archive.org, I've not checked. This ahs step-by-step
procedures for trackign down faulys.
Be warned that the 1541 is not identical to other foppy dirves, So some
detials in a generic floppy drive repair manual -- in particualr relating
to the stepper motor control -- will not apply.
Does anyone have - or have a link to - a basic text on floppy disk
troubleshooting & repair? For instance, I need to know what I should
expect
to see coming off the read head, and the read
head pre- and
post-amplifier
circuits.. basic low-level info of that ilk.
You'll see almost nothing at the heat, it's a very low level signal. The
place to look is the output fo the first amplfiieri nt he read chain
(this is normally a 733 or NE592). It has differential outputs, connect a
'scope with differential inputs (if you have one) there.Of course gettign
a signal there depends o nthe first stage of the read circuit working
correctly. But if you _don't_ get a signal there, you know where to start
looking for the fault.
What are the problems with the 1541s?
-tony