Re: GSOS Problems

[aw133@lafn.org (James Poore)]

In a previous article, norman.dodge@techall.wa.com () says:

>Can anyone tell me why the ground pin and the - or black wires of the
>Apple 2qs standard power supply are isolated from one another.  On the
>Apple //e they are definitly common to each other.
>
>On Steve Buggie's power supply they are commomn also.
>
>Is this a design change between the Apple //e and the Apple //gs?
>
>Any thoughts anyone?
>
>Norman.dodge@techall.wa.com
>
Yeah...a lot of thoughts :)

A well-built switching power-supply will have ALL the power sections 
isolated from each other.  This reduces noise from one section entering 
another section.  Also good PC board layout will also have all the 
grounds isolated.  Of course you may be asking, if the power supply have 
their grounds isolated and the board with their grounds isolated how 
would the grounds be common?  They wouldn't.  In laying out a system from 
the ground up (no pun intended), provisions must be made for a grounding 
system that will 1) Supply power with as little extraneous signal as 
possible.  2) Have no power loss thru the innerconnecting.  and 3)  To 
keep radiating signals to a minimum.  Usually, but not always, this 
involves keeping grounds isolated on the PC board and have them connect a 
only one point inside the power supply where supply impedance is the lowest.
There is no substitute for high gauge (smaller number) wire to get the 
power from the supply to the board.  The connecting wires, if long 
enough, should have a ferite bead encirling the all the supply wire to 
lower line impedance and to reduce both incoming and outgoing stray signals.
In ROM01 GS's (I haven't seen the inside of a ROM03) the 2 ground wires 
are not enough for good supply transfer.  Also the Molex connector is 
only moderately fair as a supply connector.  But one big help on the 
molex is to use their tri-furicon connector.  It surrounds the pin on the 
board on three sides as opposed to the original pin having contact on 
only one side.  My GS burned the pins on the ground wires and had to be 
replaced.  My recomendations for supply transfer would be minimum 4 wires 
for +5V and grounds, 2 wires for the +12 supply and one each for the -5 
and -12 supplies.

Jim

-- 
James M (Jim) Poore--Apple II's Forever--Especially IIgs's
Los Angeles Free Net---aw133@lafn.org
Pro-Palmtree BBS---jpoore@pro-palmtree.cts.com
"Using Computers for Mental Floss"