Hi All,
What John and Steve are saying is very
true, if you keep an eye on ebay they are out there, not all the time but they
do come up. I got a Cromemco 21 slot the other month for $40, granted it needed
some work.. but they do exist. if you can get ahold of a board that isnt in bad
shape you are off to a good start. however for those of us outside of the US
and who dont want to go through redirect companies for shipping and end up
spending 2-3x the item cost on just shipping, getting a bare box/ chassis or
even a board is a little bit more difficult. if one were to want to build a
brand new board then yes.. its gana cost.. as we see above.
with respect to the ATX power supply to
drive a system, what Steve is saying is true, they dont have huge caps in them,
they can deliver current and are tried and tested for all of our computers
todate, but the +-16 and +8 of a sizable
system, you would really want to test it out or move to a big transformer
bridge rectifiers and big caps. the problem we end up meeting again is cost..
transformers and big caps are expensive.
the best bet IMHO would be to hold
tight keep your hat on and play the waiting game for a while, saving some cash
at the same time. if you get lucky on ebay with an old system/chassis and/or
board (thats in good condition).. for a fair price then your onto a winner. if
you have done enough waiting and there still nothing around that you like.. you
weigh up the options of new gear.
with respect to the mentioned 18 slot
board, i think there seems to be a little confusion about how the ATX PSU and
board tie into the backplane. please donot confuse the two. the backplane
itself (no atx board attached) is a separate board from the ATX board. the kit is
2 (two) boards. one 18-slot backplane board and one ATX PSU board. the backplane
board is a normal nothing special 18-slot active terminated S-100 bus board, the Active termination is a direct copy
of the circuit CompuPro use for termination and the same termination used on
John Monahans board supplied by the computer project (so i take no credit for
this). it will wire straight up to your +16, -16, +8 and GND power inputs
of your S-100 compliant power supply, you can use it without the ATX board. For
intents and purposes you can throw the ATX board at the cat and forget about it.
the backplane board is just another active terminated S-100 bus board. the ATX
PSU board however is a separate board that has a 24 pin ATX connector on it
(accepting the 20 or 24 pin ATX plug) it has a terminal block output that you 'could'
wire up to the input of your S-100 board backplane IF you 1. did not have the
need for exactly +16 -16 and +8V. 2. wanted to wire up +5 onto your +8v rail if
you ran cards without onboard voltage regulators, 3. could wire up the +12,V
-12V, +12V to the "+16, -16, +8v" rails if you wanted. you could even
(by way of modification wire up 3.3v to any other rail on the s100 bus if you
needed 3.3v out somewhere). the ATX PSU board is just a nice little board to
have if you have a small system (or large ) and dont need the exact IEEE696-1983 voltages on the
rails. and have vetted your ATX PSU for output current and "quickness to
supply". +12V input to a LM7805 will still give you +5 out. Or have cards
without voltage regs, you choose what you put on your power rails. It also works
prity nice to use your salvaged ATX supply for a lab PSU. the ATX PSU (we could
call it a sub-card) has: +12v, +5v, +3.3v, GND & -12v output on its
terminal block. The ATX
board uses a small PIC microcontroller to act as the "debounce"
switch (on/off) as its about expensive as the amount of 7400 series devices i
would have used to put on the board to do the same job. i realize this may cause
some "Ahhhhh Errrrrr" for some users.. but the code and programmed
devices can be supplied if needed. I just thought i needed to clarify this before any pre-orders happen or
before i even post pics of the board design.. Note: these boards are a
"work in progress" i still have to clean up a few tracks & footprints.
please excuse the long message.. especially Vince if you have not been caffeinated
yet ;-)