Re: Re: D9090 back to life !

From: William Levak <wlevak_at_SDF.ORG>
Date: Sat, 1 Feb 2014 05:47:39 +0000 (UTC)
Message-ID: <Pine.NEB.4.64.1402010535030.19159@sdf.lonestar.org>
Rf signals are generated by various components on the boards.  The 
interfering signal is not uniform.  Moving the boards relative to each 
other may move the interference source far enough from the sensitive part 
of the circuit.

Also, the interfering signal is not only on the high side of the circuit, 
but also on the ground side.  Connecting the grounds together may damp out 
part of the interfering signal.

The ultimate fix for interfering signals is to put a conductive shield
between the source of interference and the sensitive circuit.  This is 
usually connected to ground.  It could also be connected to a constant DC 
voltage, but this has other problems.



On Mon, 27 Jan 2014, hwarin@neuf.fr wrote:

> I'm eventually suspecting this also .... they are 2 big copper leafs, one under HDD's PCB, and one under DOS board ... one side of each leaf, touching the PCB  is isolated, but none appears to be grounded on any point. As I also had to extend fixations of SASI board, may be did I missed something on chassis grounding for this board ... Does anyone have an idea on this perticular point ?
>
> I had the same symptoms with the other,nearly identical, ST225; may be are they more sensible ? In all cases, this does not explain why RF interference could be present in 1 position and absent when the entire system is rotated 90° clockwise
>
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>
> ========================================
>
> Message du : 27/01/2014 19:14
> De : "William Levak " <wlevak@SDF.ORG>
> A : cbm-hackers@musoftware.de
> Copie à :
> Sujet : Re: D9090 back to life !
>
>
> On Mon, 27 Jan 2014, hwarin@neuf.fr wrote:
>
>> Don't ask why, it operates well only when placed on it's right side ! (seen
> from ST225 manual, it's forbiden to use it from it's back .. and it's
> the exact position choosen by commodore)
>
> If it's not the bearings or the head stepper mechanism, it could be rf
> interference between the drive controller board and the main controller
> board. I've seen some IBM drives that would only work in certain
> positions because of rf interference. Try unmounting the drive and moving
> it as far away from the rest of the unit as possible. If it works that
> way, it's rf interference.
>
> Try adding a ground strap between the two boards.
>
>
>
> wlevak@sdf.lonestar.org
> SDF Public Access UNIX System - http://sdf.lonestar.org
>
> Message was sent through the cbm-hackers mailing list
>
>

wlevak@sdf.lonestar.org
SDF Public Access UNIX System - http://sdf.lonestar.org

       Message was sent through the cbm-hackers mailing list
Received on 2014-02-01 06:00:02

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