User`s guide

* Except for PC power supplies, good four-output models with a -5V output
seem to be rare. You can add a simple -5V regulator circuit to the -12V output
to obtain -5V.
As more and more new surplus power supplies are dumped, part of your
shopping challenge is finding one which is _small_ enough to work well with the
Apple II. This explains the price guideline. If a unit costs more than $20, the
odds are pretty good that it's too big physically or electrically.
Too big electrically? In general, power supplies need to be loaded in order
to do a good job of regulation. A 25-Amp output which is called upon to deliver
1 or 2 Amps is more likely to exhibit problems with feedback and regulation than
were it asked to deliver, say, 5 or 6 Amps. An Apple II with a few power-sucking
Slot cards will work fine with many PC power supplies; a base system with no
cards could have problems adequately loading some PC supplies.
Your best choice for an in-the-case replacement is likely to be some $10-
$15 unit rated at a total of less than 125 watts which was originally designed
to power a printer, monitor, or portable PC. Probably, it will be "open frame"
with no case, switch, fan, or power cord.
Installing a power supply unit-- i.e. one not specifically designed for the
Apple II-- inside your Apple II can involve a fair amount of work. When I did
such an install on our II+, the most time-consuming part was fixing up a way to
mount the On/Off switch and AC cord socket in the usual power supply opening in
the back of the case. (Mounting the stuff on a small plastic panel set into the
opening worked fine.)
The power supply board itself mounted nicely on spacers in the space
provided for the standard PS. Once the AC and various DC lines were connected,
the new PS came on-line without a hitch. Our II+ hasn't had any power supply
problems since.
______________________________
From: Rubywand, Marvin Miller, Michael Mahon
005- Could you please explain how adding thicker wire
will decrease noise on the +5V and +12V lines? I
received and installed my new "Heavy Duty" A2 power
supply and get the same results with my Second Sight
board as before-- it still locks up the computer on boot-
up.
The leads coming from most Apple II power supplies have a low resistance--
much less than 1 Ohm. (Thanks to Michael Mahon for driving home this point!)
Even so, as a user piles on peripherals and the current load increases, a wire
lead's resistance may prove to be too high to allow maintaining proper operating
voltages and low system noise-- e.g. you routinely get "FATAL SYSTEM" errors.