Req: Help/Advice on Cromemco System
M H Stein
dm561 at torfree.net
Sat Oct 18 00:50:22 CDT 2008
Date: Fri, 17 Oct 2008 18:01:40 -0700
From: "Chuck Guzis" <cclist at sydex.com>
Subject: Re: Req: Help/Advice on Cromemco System
On 17 Oct 2008 at 12:21, Dave McGuire wrote:
> > Since I have been unable to find any power supplies which provide
> > the +/- 8 and +/- 16 volts, I just thought of an idea the other day
> > of using a PC power supply and shorting out the on-board voltage
> > regulators to allow them to work at the +5V and +12V of the power
> > supply. In order to do that though, I would need a small (3-5
> > slot) motherboard to test a couple of cards together.
> I don't think it's going to be possible to short around the +5 and
> +12 regulators in a PC power supply, as they're not discrete in that
> way. Your best bet (IMO) is to surf eBay for an big open-frame
> linear power supply.
Brute-force linear is definitely the way to go.
I'd be tempted to grab a couple of filament transformers, a couple of
bridge rectifiers and some big caps. The great thing about S100
power supplies is that PSU regulation isn't important. A 6.3VAC
filament transformer hooked through a bridge rectifier and a big
electrolytic should be close enough. +/-16 could be furnished by a
small 12.6v transformer.
The real job of regulation is furnished on each board (usually
something like 78xx 79xx linear regulator ICs).
A misunderstanding, I think: he's talking about shorting out the
regulators on the *cards*, not in the PSU, and running regulated
+5 & +/-12 on the bus; should be doable with a heavy enough
bus and sufficient bypassing, in fact I think some manufacturers
did indeed do just that.
I have a Cromemco PSU BTW, but probably not worth shipping.
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