Re: oh, no: 2 questions

[Rubywand <rubywand@swbell.net>]

Jeff Blakeney writes ...

 ....

> 
> I recently set up a IIgs system in my bedroom and placed the computer
> system right beside a Commodore 1702 composite video monitor that I
> have connected to a Beta VCR that I use as a TV.  This IIgs has the
> standard power supply installed and when I power it up with the "TV"
> on, I get a lot of "noise" on the 1702's screen.
> 
> If it generates that much noise while the shielding is intact, I'd
> hate to see what it does with the shielding broken by not having the
> power supply in place.
> 
> However, I did run a IIgs for years with no IIgs power supply
> installed but I never placed it anywhere near things that would be
> affected by the noise it generates.
> 
 ....

     For years we ran our IIgs with full shielding. It produced
significant interference with radio reception in a portion of the AM
band on an AC-only-powered receiver in the same room about 10' away. TV
interference was minimal on a TV in the same room. Radio interference
was virtually non-existent on newer AC/DC receivers (running on AC or
batteries) in the same room.

     A few years ago, the shielding was removed because it blocked air
flow and was a shorting hazard for the motherboard. There was no notable
change in interference level.

     The power supply is still in place because it is needed to supply
power. Perhaps it helps prevent more interference; perhaps, not.

     One indication of the unpredictability of electromagnetic
interference is the 'cure' for interference on the susceptible radio in
the room. We just turn ON a printer-- one connected to a PC-- and the
interference is greatly reduced. The printer is powered from the same AC
plug as the IIgs; but, then, so is the PC and turning it on is no help.

     In your experiment with the VCR, you had an interference problem
and, logically, figured that removing the shielding would make things
worse. However, if the interference is, chiefly, propagated via the
power line, removing the shielding may have made nearly no difference.

     Each user's situation is different. If someone lives in a dorm or
apartment, the need to check with neighbors makes experiments with
removing shielding and/or an unused power supply difficult. Otherwise,
the benefits of getting rid of shielding and an unused power supply make
experimentation worthwhile.



Rubywand