RE: C64 TOWER
                                       
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From           Raymond Carlsen <rrcc@u.washington.edu>
Date           Fri, 6 Mar 1998 19:46:31 -0800
3   

> In order to get the 9V I needed for the
> C128 motherboard, I actually mounted a C128 power supply inside and hooked it
> off the same switch as the PC power supply.  I even insulated the extra PS
> against any sort of radiations and added a little fan to boot.  This strikes
> me as awful though, and I've always hoped to get better ideas from someone.
> Does anyone know a power supply maker that makes 5V/9V/12V power supplies
> that fit in tower cases? 

     Nobody else makes a multi-output supply with 9VAC output, I'm afraid. 
I would go with the original tower case IBM supply and install a small 9VAV
transformer somewhere inside the tower. Radio Shack has a 18VCT (18 volt
center tapped) transformer that would work... just use the center tap and
one of the outer legs for the 9 volts. The RS part number is RSU 10524239,
but any other vendor could probably supply a "generic" 9VAC @ 1Amp.
     An IBM power supply outputs +5 volts DC at anywhere from 5 to 25 Amps
(much more than you'll ever need) and +12VDC at from 2 to 10 Amps. With
those two outputs, it can run the drives too. It also outputs -12VDC and
-5VDC (not needed). PC supplies have a fan built-in. Since they are
switchers, you can't tap off the 9 volts AC from them... they run at very
high frequencies, not 60 Hz.  So, it's necessary to add a small transformer
for the 9 volts which -must- be isolated from ground to work properly... 
another reason not to try and modify an existing non-CBM supply. 
     Note: if you're working with PC power supplies, be aware that they
require a minimum load to work, otherwise they shut down or will not start
up. The minimum recommended load is at least 10% of the maximum power
output on the +5 volt line. I've repaired those supplies, and for test
purposes, I use an automobile taillight (dual filament). I wire the heavier
filament to the +5 volt output (the red wire), the smaller filament to the
+12 volt output (yellow wire), and common to ground (black). The 128 will
provide enough of a load to the supply. Just don't let a PC supply fool you
into thinking it's dead if there is no load on it.

> Anyways, my other big issue is power for the RamLink.  It needs constant
> power, but it strikes me as silly to actually mount the little transformer
> in there... and an external port just for this power supply seems silly too,
> and yet that's all I can think of.  Any other ideas?

It's probably the easiest, unless you want to dig inside the PC power
supply to get the "always live" AC input for the RAMLink supply. One
additional power cord to the wall or plug strip is not so bad. You could
also go with rechargeable batteries (a large pack) inside the tower to run
the RAMLink, powered and recharged by the PC switcher when it's on.

Note that I've never done a tower install like this... these are only
suggestions. Wish I had more time to "play". I'd probably tackle it. 

Ray Carlsen CET
Carlsen Electronics