Req: Help/Advice on Cromemco System

M H Stein dm561 at torfree.net
Sat Oct 18 00:50:22 CDT 2008


----------Original Message:
Message: 28
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).

Cheers,
Chuck
--------------
-----------------Reply:

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.

mike





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