Re: SecondSight boot stability

[rubywand@aol.com (RUBYWAND)]

In article <32160EF8.6855@Carver.agn.net>, Bill Carver
<Bill@Carver.agn.net> writes:

>
>Before you blame the second sight card, check your power supply.

     When SS is the only Slot board, it seems less likely. Still, SS is
said to place a significant demand on the +12V line. This could produce
enough voltage drop across the skimpy +12V power supply lead to induce
noise which could bomb the system.

 
>They're dropping like flies now.
>-- 

     True; and, really, it's too bad. There is good reason to believe that
"power supply problems" are, mainly, power supply lead problems. As long
as most users were running at fairly small loads, the power supply looked
fine. When we started to add hot accelerators, RamFAST's, and Second Sight
boards, the power supply suddenly "went bad".

     Our Woz IIgs is one of the first two sold in Houston back in 1986. It
has the original power supply and works fine loaded with the usual
accelerator, RamFast, Focus Hard Card, etc.. Its power supply "went bad"
when we added the 10MHz Zip-GS. Fattening the PS +5V and GND leads cut
glitching significantly. On the motherboard, adding #16 gauge wires from
the +5V and GND PS connector pads to +5V and GND points on Slots 3 and 7
finished the job. (Second Sight board users may need to fatten the +12V
lead, too)  Anyway, no glitches-- the power supply "went good".

     The standard IIgs power supply is rated at 4 Amps (+5V); but, due to
skimpy leads, cannot actually run a system which pulls more than about
2.5A on the +5V line. At around 2 Amps, the voltage drop from PS to
motherboard starts to be significant in terms of noise spikes. At higher
loads, the at-motherboard voltage edges downward; noise levels increase
and noise immunity decreases.

     Swapping in a new "heavy duty" supply may, sometimes, fix glitching
because the leads happen to be a bit heavier and/or shorter. The new
supply may run at a slightly higher voltage, too; and, perhaps, the new
supply comes with a gold-plated plug. (Sometimes, especially when the load
is fairly heavy, a new PS will merely reduce glitching or make no great
difference.)  Users are unlikely to find a replacement unit which tackles
the problem correctly-- i.e. the leads (at least +5V and GND)  need to be
'really fat'.

     Basically, most "bad" IIgs supplies are, probably, just fine.
However, the skimpy PS leads are a humongous design flaw and should be
replaced. (A very nice cure would be to use #14 gauge silver going to a
gold-plated plug.)


Rubywand