Clicking IIgs'

[oz390gta]

I have a ROM01 and a ROM03 gs which both make a continous clicking
sound through the speaker when running GS/OS. This clicking does not
happen when in Prodos or when the system is interupted like holding
down the mouse button or a key. I once read it had something to do
with the 5.25 drive, they even do it with no drives connected. I have
another ROM01 that does not click so I put that power supply into the
other two, they still click.

Any ideas?

oz390gta

[David Empson]

[Moving this back to comp.sys.apple2 as it is nothing to do with
communications.]

Post by oz390gta
I have a ROM01 and a ROM03 gs which both make a continous clicking
sound through the speaker when running GS/OS. This clicking does not
happen when in Prodos or when the system is interupted like holding
down the mouse button or a key. I once read it had something to do
with the 5.25 drive, they even do it with no drives connected.

It isn't the 5.25" drive: it is the 3.5" drive that is being polled.

As long as Finder is running or you have a file selection dialog open,
and sitting idle in the main event loop, the system is polling every
connected 3.5" drive once per second to check for a changed disk.
Holding down the mouse button gets out of the main event loop until you
release the button, which temporarily stops the polling.

The clicking sound is due to induced noise travelling into the sound
circuitry via the power rails, as polling the 3.5" drive causes a brief
power surge on the +12V rail.

I was under the impression that the improvements in the ROM 3 design
reduced or eliminated much of the noise being picked up the sound
circuitry, but clearly your ROM 3 still has the problem (mine didn't).

Post by oz390gta
I have another ROM01 that does not click so I put that power supply into
the other two, they still click.

It isn't the power supply - it is the circuitry on the motherboard not
dampening the noise sufficiently, possibly influenced by the specific
characteristics of the 3.5" drives involved, or other devices installed
in or connected to the computer and the load/dampening effect they
impose on the +12V rail.