External Disk Intrusion

[Gene Heskett]

On Wednesday 08 January 2020 09:01:35 Liam Proven wrote:

> On Wed, 8 Jan 2020 at 13:43, Phil Dobbin <bukowskiscat at gmail.com> 
wrote:
> > parted reported it was a SCSI device: it's a USB HDD.
>
> I thought it might be. That is what, in my attemptedly-humorous way, I
> was trying to establish.
>
> The thing is that actual SCSI cabling faults are very hard to
> diagnose. We used to have internet jokes about them and the need for
> sacrificial goats or chickens, but of particular colours for different
> cable types, pentagram drawn in blood, holy candles, etc.
>

And all that pickityness can be laid at the feet of a bean counter 
between the interface card designer, who specified a $2.00 schotkey 
diode for buss isolation, which had a maximum voltage drop across it of 
perhaps .1 volts, and changed to have an 8 cent Si diode with .666 volts 
drop across it, thereby lowering the logic one voltage by .45 volts.

Since the logic one at the logic chips inputs had to be at lease 2.2 
volts, and the nearest set of termination resistors gave 3.0 volts when 
this buss isolation diode was replaced with a short, but with the cheap 
Si diode in there gave a logic one voltage closer to 2.4 most of the 
circuits noise margin was used up and considering that same bean counter 
crossed out the 5% terminators in favor of 20% tolerance, the result was 
predictable.
 
The situation was much better when active terminations came into use, but 
by that time the scsi buss's reputation was doomed.

But back in the day of the bottom 190 market tv stations were generating 
their on air gfx needs with a bank of Amiga computers, every scsi card 
that came in the door, if the engineer was worth his paycheck, that 
diode was replaced the first time the Amiga it was in, crashed.  End of 
problem except for one Trump Card, where in traceing that card, I found 
the termpacks had been soldered in bass ackwards. It was easier to cut 
and jumper the supplies traces than to unsolder the packs and turn them 
around. So I did that in addition to swapping out the infamous diode.

We, in a middle 160's market, were the first to put our news on the air, 
out as a webpage, which led to legal problems because CBS fussed about 
their copyrights, so we had to filter any web content that came from 
CBS, but that didn't last long after their bean counters discovered 
there was money to be made.  That was all driven by ARexx and delivered 
by dialup from that Amiga in those Jurrasic (in web time) days.

Who am I to criticise the makers of that stuff?  I have an 8th grade 
diploma, but I am also a CET. Look that up if you care.

> And the answer was that it was always a termination problem anyway.
>
> But with USB it's easier -- and cheaper -- to troubleshoot.
>
> Things to try before you start disabling major system functionality
> like automount:
>
>  • Is the device bus-powered? If so, try it on its own PSU.
>  • Try a different USB cable.
>  • Try a different USB port.
>  • Try connecting it via a powered hub, not directly.
>
> --
> Liam Proven - Profile: https://about.me/liamproven
> Email: lproven at cix.co.uk - Google Mail/Hangouts/Plus:
> lproven at gmail.com Twitter/Facebook/Flickr: lproven - Skype/LinkedIn:
> liamproven UK: +44 7939-087884 - ČR (+ WhatsApp/Telegram/Signal): +420
> 702 829 053


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>