RE: Re: 1541C troubles

From: Bil Herd <>
Date: Fri, 6 Jul 2012 21:19:34 -0400
Message-ID: <>
Do you mean it can't read _any_ track or that it can't read the
_specific_ track that it thinks it is looking for?

-----Original Message-----
[] On Behalf Of William Levak
Sent: Friday, July 06, 2012 1:29 PM
Subject: Re: Re: 1541C troubles

It's not a problem of alignment.  It's a problem of programming logic.
The drive occasionly gets in a state that the programmers did not
anticipate.  The head moves, but does not do anything, because it cannot
find the track it is supposed to be on.

The fix is to step the head all the way out and then back in again.  The
test routine does this.  You could also do this by issuing the commands to
read track 35 and then track 0. A calibrated disk is not necessary, you
only need a disk with the track and sector headers written correctly.

Moving the head by hand sometimes works, but the test routine is more

On Fri, 6 Jul 2012, wrote:

> William,
> This 1541C has not a problem to move the head and even if it's
misaligned (it could not misalign that much in a minute or so) it should
be able to format a simple floppy and read it back - To me, the problem is
"somewhere" in read/write logic but I don't know where to start searching
on this board revision.
> Regards
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> ========================================
> Message du : 06/07/2012 07:18
> De : "William Levak " <wlevak@SDF.ORG> A :
> Copie  : Sujet : Re: 1541C troubles
> If 1541 drives crash while the head is too far out, they cannot find
> their way back to the home position.
> Use the drive test routine on the demo disk to reset it. You will have
> to load the test routine from another drive unit, and run it. It steps
> the head all the way out and back in again. If this doesn't fix it,
> you have a real hardware problem.
> On Thu, 5 Jul 2012, wrote:
>> Hi, Friends
>> I am in trouble with a recently acquired 1541C (white 1541 case, white
newtronics mecanic) and I need your lights !
>> My first remark when it arrived was that the fuse support was damaged
and metal body support slightly blend. Except from this, noting noticeable
and it was operating surprisely well.
>> After few days of use it bruptaly crashed (in software I mean ...)
while running a very recent C64 demo. Power cycled eveverything and
thought all will continue to go allright for next dozen of years - but no
>> The drive work absolutely normally in apearance but is completely
unable to read or write anything at all. Spn motor works okay, stepper
is also okay, IEEE communication is okay but it's impossible to read or
even format any floppy disk.
>> I've done all easy things - cleanned the head with isopropyl alcool,
reseated all connectors, swapped both 6522, checked 12V and 5V but no
change, it still won't read/format anything. I've searched the web for a
situable service manual/schematics and found that my MainBoard is labelled
251854, what seems to be PCB#250448. I don't have any spare
Mitsumi/Newtronics mecanic to swap so I can't determine if mecanics is
definitely okay or not.
>> The board has an hybrid UD1 as -02 a ROM UA2 as -01 and a gate array
UC4 as -01 - This seems to be a very standard board.
>> I've tested head's wire continuity that is okay for all wires but I
can't find any reference for expected values - I've values for ALPS for
pin 1-5 that should be 32 ohms - I'm currently at 24 ohms. If I take pin
1-3 or pin 3-5, I have 12 ohms, so, what seems to be coherent.
>> Can anyone confirm value of 24 ohms for a good head in newtronics
mecanic ?
>> Does anyone have a better idea than removing the shield soldered under
the PCB and reheat all points around UD1/UC4/UC5 plus all discrete
components involved around ?
>> Regards - Thanks for your help
> SDF Public Access UNIX System -
SDF Public Access UNIX System -

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Received on 2012-07-07 02:00:27

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