Re: Question Soup (shielding, ColorSwitch, 16k ZIP)

[rubywand@aol.com (RUBYWAND)]

In article <4msok0$e7q@atlantis.atlantis.actrix.gen.nz>,
dempson@atlantis.actrix.gen.nz (David Empson) writes:

>In article <4mm0dk$hvl@freenet-news.carleton.ca>,
>Dan Markarian <ae196@FreeNet.Carleton.CA> wrote:
>> 
>> I would be very grateful if someone could shed some light on these
q's...
>>  
>> (1) When I mount my IIgs in a tower case, do I attach the tower case
>>     ground to the GS' cage?
>
>The IIgs cage should be connected to earth, not to signal ground.
>

     The third wire in the AC power cord (a green lead in the U.S.) is
normally connected to the PC case frame and metal cover screwed onto the
frame via the Power Supply box or a separate lead. The home or building AC
power wiring should include one or more grounding rods sunk into the earth
(ground, dirt, clay, ...)  which send the 'green wire' to Earth Ground.

     Earth grounding is chiefly a safety measure. Should 'hot' AC somehow
get from internal circuitry to the metal case it will be grounded.
Something (a fuse, capacitor, etc.) may blow inside the case; but, a user
will be saved from touching a 'hot' case and being shocked.

     Earth grounding the case also helps suppress Radio Frequency
radiation from circuits inside the metal case. However, all PC cases
'leak'. Some RF will get to the power lines and some radiates from
keyboard, mouse, etc. cables.  

      
>> (2) The GS is mounted on its side with the cards properly supported in
>>     the tower, without the GS' original top cover.  Do I also need to
>>     set up the metallic cage previously part of the the GS' top cover
>>     above the expansion cards?
>
>It would help to reduce RF interference if you can do this.

     Putting the IIgs top metal shield in place involves a trade-off.
First, there's the bother of finding a way to do it-- not so easy without
the mechanical support of the plastic lid. The metal shield will reduce
air-flow. The shield is also something of a hazzard. Should it slip, you
could end up shorting any number of Slot and motherboard circuits.

     You can tune a radio (placed several feet away from the computer) to
a frequency where interference/noise is greatest. (Make sure the
iterference is coming from the computer by turning the computer OFF-- the
noise should decrease greatly.)  Check noise with the top shield on and
with it off-- for both conditions, the PC case cover should be in place
and connected via at least one metal screw. Decide for yourself if the
metal top shield helps enough to justify adding it.


>
>> (4) Attaching my monitor via my PC Transporter ColorSwitch causes a
>>     kind of slow flickering and a moving wavey 'pattern' to the GS'
>>     image.  I tried placing the ColorSwitch as far away from the
>>     motherboard and power supply with no visible difference.  What
>>     could be causing this?
>
>The ColorSwitch does introduce a little distortion and lowering of the
>signal levels.  The extra cabling probably increases its sensitivity
>to environmental noise.  I don't get flickering, though - you might
>have a faulty ColorSwitch.
>
>The wavy pattern you describe sounds like an interference pattern
>(beating) with another monitor or power supply running at the same
>scan frequency.

     If the PC Power Supply is switching at some frequency approximately
equal to your monitor's horizontal sync or approximately equal to half
your monitor's horizontal sync and the PCT circuits increase sensitivity
to circuit noise, then you may have a problem which will be very difficult
to cure. Both switching noise and 60Hz AC hum will plague monitor
performance. 

     Or, the cure could be very simple: pull the PCT and sell it to
someone with a normal IIgs setup. Use the money to buy a surplus PC and
use a NULL-modem setup to transfer stuff back and forth to the GS. All of
your for-PC stuff will work better and your GS monitor will display nice
sharp stable images!
  


Rubywand