Re: 911 Fatal Error on TransWarp GS?

[Rubywand <rubywand@swbell.net>]

"Michael J. Mahon" wrote:
> 
 ....

> Actually, there isn't much to an 18-gauge wire except resistance, inductance,
> and capacitance, and all those are addressed in my reply.  Assuming only
> that most of the strands are not broken, the analysis stands without change.
> Note also that a break in half the strands is bridged by the fact that strands
> are not insulated from one another, so that the incremental increase in
> resistance is very small (though in extreme cases, local heating could be
> a problem).

     Yet, measurements indicated a significant drop across the +5V line at 3
Amps. Perhaps the lne is not truly 18 gauge. Perhaps a flaw in PS sensing and
regulation is a factor. Whatever, going to heavier lines eliminated the
apparent drop. 


> 
> Nothing in my analysis depends on how "ideal" the power supply is--only
> that it meet the voltage, current, and filtering requirements of the Apple II.

     Which is not always a valid assumption. For instance, plugging in stuff
like accelerator boards often leads to a rash of "mysterious" system crashes,
increased noise in audio outputs, etc..

     If swapping in heavier leads did not so often solve such problems, then,
there would be no particular reason to suspect that the original leads are too
skimpy. Since heavier leads reduce or eliminate the problems, it looks like
swapping them in is a good idea.


> 
> Except for ripple, which should be in the millivolt range, the power supply
> voltages are, indeed, DC.

     The voltage through a line is always, to some extent, modulated by changes
in the load. Besides the PS leads, the IIgs has many power lines (traces) which
act as resistances across which voltage is modulated.


>  My analysis assumes that the poser supply is
> properly decoupled for high frequencies by the main board, and for low
> frequencies by the power supply filter capacitors.  If this is not true, then
> the problem is not in the wires, but in the decoupling components.

     Most likely, in the IIgs, it is both. For instance, it is widely known
that the ROM-01 board Slot card power traces are too skimpy and/or not
adequately bypassed.

     Regarding the rest of the motherboard, 'adequate bypassing' will depend
upon what is supposed to be bypassed. Adding an accelerator, PC transporter,
Second Sight board, etc. increases high-frequency load modulation and, thus,
line noise. If we reduce an important noise source-- e.g. replace the chief
power supply leads-- then,  motherboard bypassing may be roughly adequate.
Jumpering the main power lines on the Slot plane-- e.g. from the PS connector
to Slots 3 and 7-- further reduces noise generation.

 ....


> The reasons for power supply failure are pretty much the same for all
> switching power supplies:  line transients, temperature, and time.
> 
> A single large line transient can take out an input diode, and consequently
> a fuse and/or and input capacitor.  Repeated smaller line transients can
> do the same over time.
> 
> High temperatures accelerate aging of all electronic components, but
> expecially electrochemical components, like electrolytic capacitors--
> most often resulting in lowered capacitance and/or higher equivalent
> series resistance (ESR).  Both effects contribute to lowered filtering
> capability and lower power supply margins against specifications.
> 
> Finally, time increases the cumulative probability of both random
> failures and wear-out or stress failures.  Again, it is the electrolytic
> capacitors that are the most probable victims.

     Will agree that there are several good candidates for explaining IIgs PS
failures. We acquired a System Saver IIgs fairly early. So, supposedly, our
IIgs PS has been at least somewhat protected from line transients for most of
its 16 years. It's hard to estimate how much good having air blow across part
of the outside of the PS case has aided PS cooling.

     It would be interesting to know how many System Saver IIgs users have
experienced PS failures.



Rubywand