Re: Two 1541-II drives with problems

Hello Ville,

* On Wed, Apr 23, 2014 at 11:01:24PM +0300 Ville Laustela wrote:
 
 
> Sorry if I forgot to mention the ZoomFloppy. I'll send you the ROM,
> Spiro. It didn't take very long to transfer, and yes, it is 16384
> bytes.

I just checked: It is a plain 251968-03 ROM; that is, there is no sensor
for track 0.

> Didn't do file comparasion as OS X's terminal didn't accept it
> as fc /b, didn't go to search for correct syntax now. It is a 1541-II
> (as per the topic).

I thought you were using WinVICE to test? That's why I assumed you are
on Windows, and I proposed "fc". For Unixoids, I would have proposed
"diff" instead, although I do not know if it exists on MacOS, too.

Thanks to silverdream, we now know that you can also use "cmp".

> If I run the cbmformat command, I can see that the drive head makes a
> very little step (but won't move anywhere).

That's bad. That's why I asked about the ROM version: If it were with a
track 0 sensor, then the little step might make sense if the head is
already on track 0 (or 1). However, your drive does not have this
sensor. Thus, the head should bump. Unfortunately, it does not.

Thus, my possible candidates would be (according to the schematics on
http://unusedino.de/ec64/technical/misc/c1541/1541-II-340503.gif):

- the DC VIA (6522, U8)
- the gate array (U10)
- U13 which seems to be the amplifier for the stepper motor
- the drive mechanics themselves.

Of course, one could more tests to find out what the 6502 reads to be
more sure.

However, I would really bet on the 6522. You might want to swap it with
the 6522 in U6. If the serial communication does not work then, it is
the 6522.

But, as you state below that you have swapped in a 6522, then the
next-best bet comes into play: the gate array. It is responsible for the
stepper motor as well as for the (digital) R/W logic, as well as
generating the BYTE signal (which is directly connect to "S.O." on the
6502).

However, I do not know where you could get a replacement for that one.

In order to find out what we are searching, you might also want to test
your PCB against a known working drive mechanics, if you have some
access to it?


> One thing I also wonder: if I power up the drive with a floppy in and
> the door closed, it keeps running and both lights stay up. That sounds
> weird, I don't remember 1541s doing that? If I open the drive door, it
> stops. How can it see when the door is open, I thought this doesn't
> have a disk sensor?

It does not use a disk sensor. Instead, it only looks for the write
protect light sensor for changes, and then it looks if it can read
anything from disk. If it gets byte after byte, it knows a disk is
inserted.

I have not seen this behaviour myself, so I cannot tell anything about
the details. Furthermore, I am not sure if the 1541-II actually should
have this behaviour or not.

> I have now also socketed the DC 6522 VIA, and replaced it with another
> one. Still no chance. But, couple of times today cbmctrl showed me
> "drive not ready", which was something new. But then it went away
> again, almost like a bad contact somewhere. I am really getting a bit
> lost now, so many chances what might be wrong with this :/

The problem is we would need some test programs to find out what the CPU
is actually seeing from the drive in order to be able to diagnose this
better. I don't think many test programs exist.

Groepaz, don't you work on test programs for the 6522 for VICE? Can they
be made to work with the floppy drive?


Regards,
Spiro.

-- 
Spiro R. Trikaliotis
http://www.trikaliotis.net/

       Message was sent through the cbm-hackers mailing list