Re: 911 Fatal Error on TransWarp GS?

[Rubywand <rubywand@swbell.net>]

"Michael J. Mahon" writes ...
> 
 ....

> 
> What was the significant voltage drop?  How was it measured?  Did it
> include the connector?  Did it include any main board traces?  How
> much voltage drop was induced by inserting the current meter?
> 
> Have you looked at the +5 with a scope?  If the noise is present at
> the power supply terminals, then fatter leads won't help.  If power is
> clean at the power supply terminals and dirty at the main board
> connector, then, and only then, bigger leads could help.  (Again,
> proper gounding of the scope is essential.)
> 

     It's been a while since doing the measurements; so, I don't recall the
details. The check was done outside of the IIgs into a purely resistive load.
Removing the current meter would have been my usual practice for doing final
voltage drop checks on low R leads. Pretty sure the drop at 3 Amps was around
.3V or so. Don't recall putting the scope on power check points in the IIgs. 



> Have you tried simply replacing the wires with known-good wires of the
> _same_ guage?  Ohm's Law is not just a good idea--it works!  ;-)
>

     Replacing the main PS lines is sufficient bother so that, when you do it,
you make sure to use heavier wires.

 ....
 

> > For instance, plugging in stuff like accelerator boards often leads
> > to a rash of "mysterious" system crashes, increased noise in audio
> > outputs, etc..
> 
> As would be expected on any system in which the power supply had
> become marginal relative to the load.

     If you mean that you have problems when the PS is significantly damaged,
sure.

     In most cases, though, we are dealing with good power supplies. Adding an
accelerator will seldom push the load beyond the native capacity of the IIgs
power supply. If it does-- like you have the other Slots filled with power
gobbler boards-- then, the PS should simply shut down and remove all doubt.

     Most IIgs "power supply problems" are either obviously linked to a
defective PS or they are really power distribution problems-- i.e. the lines
from the PS are too skimpy, motherboard power traces are too skimpy, bypassing
fails to handle noise produced by accelerators switching at frequencies 2-5
times the normal IIgs max, etc.. 

 ....

> >     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.
> 
> Yes, but these traces are factored into the design of the IIgs, and should
> operate properly if not improperly loaded.

     Except for the Slot card plane design (which is known to be defective),
the other motherboard lines may be fine.

 .... 

> 
> Slot power decoupling is specified to be on the plug-in cards, not on
> the main board.  You would not  want the decoupling capacitors across
> a connector from the load--in this case, the logic on the card.

     There is just so much you can achieve with on-card decoupling. The Slot
plane +5 line is definitely inadequate for many setups. For some boards, the
+12 line is probably inadequate, too.

 ....

> > 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
> >t o Slots 3 and 7-- further reduces noise generation.
> 
> Again, this indicates that either the cards are not adequately bypassed, or
> the transient loads are outside of spec, or both.  I suspect that some
> accelerators (particularly the TransWarp) are
> considerably outside the slot power spec, and
> direct-wiring the power may be compensating for this design problem.
> 

     Most likely. This still leaves the user with the problem of dealing with a
serious Apple design error. People were plugging power gobbler cards into Apple
II Slots years before the IIgs came along. Anyone who's ever designed a
computer (that works) should have known the Slot power traces would be
inadequate. 

     Similarly, the power supply should come with heavier leads for +5, +12,
and Ground. 



Rubywand