[Coco] calling all MM/1 owners

[Gene Heskett]

On Friday 25 January 2008, Kevin Diggs wrote:
>Gene Heskett wrote:
>> Look at the data line, powered up, with a voltmeter, and do whatever it
>> takes to get any resting line above 2.8 volts.  3 is ideal, but by the
>> time you've lost .65 volts in the isolation diode between the 5 volt line
>> and the top of the resistor packs, 3 can't be done.  This isolation diode
>> can be shorted out, which will help considerably IF you can guarantee that
>> there will never be a self powered drive cabinet attached to the external
>> scsi connector on the back of the card if it has one.  Its there to keep
>> an external supply
>
>Gene,
>
>	Could you replace the diode with a Schottky version? Don't they have a
>lower voltage drop?
>
>kevin
>
Sure you can and yes they do, typically in the .15 volt range, but the common 
hp2800 generic isn't quite up to the current draw, so one should choose one 
characterized for half an amp or so of fwd current.  Or just say screw it, 
and rebuild with an active terminator.  That might be stretching some folks 
ability at hardware hacking though.  It should be done on both ends as the 
active chip, faced with driving termpacks on the other end of the cable, 
might overheat & do weird things, like blow the top off the case?

One thing I've had to do when we were running amigas with scsi drives at the 
tv station, was to hack up connectors on the rear of the case to allow the 
use of generic psu's setting on the table behind them. The amiga stock psu, 
like most, will fade its 5 volt line down to 4.7 or so in about 2 years, and 
the scsi stuff then turns its toes up till the psu is replaced.  We found 
some once that actually had an adjustment pot in them so we set them for 
about 5.15 volts and everything was as happy as a clam, till they faded far 
enough we couldn't turn them back up.

Even today, I think the single most common failure of an intel/amd box, 
running whatever opsys, is the psu's 5 volt line sagging low.  All sorts of 
make you scratch yur head problems can be fixed with a fresh psu.  And the 
gamers favorite, the 400+ watt Antecs?  Worst of the bunch & no warranty.  
They always fade about 3 weeks out of warranty. So I'm back to the basic $20 
generic supply, works just as well here.  Warranty long since expired.  But 
its about due, gkrellm says the 5 volt line is 4.76, and that's trouble 
looking for a place to put its feet up and drink all your beer.

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-- 
Cheers, Gene
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