Re: 911 Fatal Error on TransWarp GS?

[Rubywand <rubywand@swbell.net>]

Frank Townsend writes ...
>
> Rubywand" <rubywand@swbell.net> wrote ...
>>
 ....
>>   If the 0911 errors vanish, it is fairly likely that the problem is system
>> noise resulting from the load represented by the TransWarp GS in combination
>> with skimpy Power Supply leads and skimpy power traces going to the Slots.
 ....
>
> I thought Michael Mahon's nicely reasoned essay discussing the resistance of
> the IIgs power supply leads pretty well debunked this hypothesis.
> 
> See
> 
> http://groups.google.com/groups?q=%22power+supply%22+mahon&hl=en&lr=&ie=UTF-
> 8&oe=UTF-8&selm=20020111033043.25525.00001341%40mb-fc.aol.com&rnum=2
> 

     Thanks for the link. Missed that message from Michael.

     Agree. He makes a reasonable case. It does depend on some ideal
conditions. 

     In practice, the lines to the motherboard are not ideal 18 gauge lines,
the power supply is not an ideal battery, and the voltages in the lines are not
pure DC.

     Most fairly filled-out IIgs systems probably draw 3-4 Amps on the +5V
line. At this level, measurements showed a noticeable DC drop across the lead--
think it was around .3V-.4V. When powering the IIgs, the instantaneous current
demand due to clocked switching of gates should be higher and so should the V's
appearing across the line (especially at high frequencies).

     So, the user should expect that gates will have lowered noise immunity and
that more noise will be present. This should lead to system crashes. 

     When programming in Applesoft or in the monitor the user is doing a lot of
ADB accesses (key presses). On a noisy IIgs, the ADB sub-system seems a fairly
likely place for a programmer to experience a glitch leading to a crash.

     Over time, the noise spikes appear to degrade Power Supply performance.
Perhaps the feedback leads to circuit conditions which damage some components.
For sure, many IIgs power supplies seem to fail for no obvious reason.


     Real world support for doing the suggested Power Supply mods is pretty
good. Our IIgs is a Woz machine with the ROM-01 upgrade. It has the Power
Supply and motherboard Slot wiring mods. It's fairly loaded-- 4MB GS-Ram III,
64k ZipGS+, RamFAST SCSI, Focus drive, Stereo Card, Mockingboard, ... . There
is a System Saver IIgs to supply cooling, etc..

     Crashes are very rare-- maybe once every ten sessions or so; and, the
Power Supply (which has never had a cooling fan attached) is, except for having
the leads swapped out,  the one that came with the computer back in 1986.

     Plus, one or two users plagued with crashes and noise who have done the
Power Supply mod report good results.



Rubywand