S-100 Bus Voltages - test-drb@ccmp.vtda.org

2 Jun 2001

From: Edwin P. Groot &lt;epgroot(a)ucdavis.edu&gt;
...
      After pulling all but one of the cards out I
powered up the system.
Fans run fine, but the motherboard voltage supplies are rather high. For
...
 +8V I measure 10.7V; for +16V I get -19.3V; and for
-16V I get -19.3V. Is
...
 this some careless engineering, bad components, or is
the board really NOT
...
 supposed to receive the nominal voltage? 

Obviously you have no expereince with S100.  The Voltages supplied to the
bus
are UNREGUALTED with a minima of +8, +15 and -15.  Each card carries
it's own local regulation to resolve the 5/12/-12/-5 as needed.

...
      Many of the S-100 boards are discoloured
brown-green on the solder
side opposite these large transistor-like things with heat sinks.  Is that
...
 something to worry about? 

Typical and those large transistor like things are voltage regulators.

...
 Does that look safe enough to put the boards back and
see how this system
...
 runs? 
The measurments you made are mostly meaningless.  Is it safe?  Likely is
but that done not mean it will run.  I'd have to assume the boards in
there
are a complete set and configured (memory and IO addresses correctly set)
for anything good to happen.  S100 was NOT plug and play.

...
      A fair amount of current runs through these slots.
 I nearly welded my
...
 probe to the slot when I accidently shorted two pins!

Obviously contacted +8 to the -16.  And yes those supplies are typically
good for 25A on the +8 and 4-8A on the +15.

Allison