External Disk Intrusion

[Liam Proven]

On Wed, 8 Jan 2020 at 17:29, Gene Heskett <gheskett at shentel.net> wrote:
>
> 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.

TBH that level of component electronics is over my head. Would you
mind if I quoted that on the ClassicCmp list and asked for comments?
Anonymously or with credit, however you prefer.

-- 
Liam Proven - Profile: https://about.me/liamproven
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