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From: grr@cbmvax.UUCP (George Robbins)
Newsgroups: comp.sys.amiga
Subject: Re: The time (my watch has troubles) has come ...
Message-ID: <2775@cbmvax.UUCP>
Date: Sun, 15-Nov-87 04:03:22 EST
Article-I.D.: cbmvax.2775
Posted: Sun Nov 15 04:03:22 1987
Date-Received: Mon, 16-Nov-87 03:51:21 EST
References: <16531@amdahl.amdahl.com> <2541@cbmvax.UUCP> <17264@amdahl.amdahl.com>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 41
Keywords: I should learn to RTFM

In article <17264@amdahl.amdahl.com> kim@amdahl.amdahl.com (Kim DeVaughn) writes:
> > 
> > This makes it compatible with the A500 which doesn't have the tick
> > coming from the power supply :-(  but must rely on the vertical
> > sync line for its timing, which we know is.........
> 
> Strange that it (the 500) doesn't pick off the line frequency ... doesn't
> seem like much of a cost savings not to.

	Well, all A500 power supplies are switching supplies, and one class of
	switcher, the kind that rectifies the line current directly and puts
	the isolation transformer after the switching circuitry, doesn't have
	any convienient 60 Hz transformer where you can pick up the line
	frequency tick.  There were some alternatives but they all seemed
	to do disproportionate things to the cost of the supply, cable and
	connectors. 
 
> An "interesting" side effect of changing the jumper from the video sync to
> the line tick, is that my floppy now *grinds* noticibly LOUDER (gak!)
> Everything is nice and tight, mounting wise, so it must be due to the
> slight difference in timer interrupt rates (resonance ?)  Sounds pretty
> fishy, but I don't have a better explanation ...

	This is flatly and completely impossible!!!  Meaning I guess we
	should try it here and see if we see the same kind of effect.
	One possibility would be that using the vertical sync signal the
	clock related software activity is always synchronized to the
	video related activity, whereas in the line frequency it would
	tend to gradually drift in and out of sync.
 
> Last night, I installed a 2nd 3.5" floppy, and *it* is REALLY quiet ...
> literally, quiet as a whisper.  It's the exact same Matsushita drive
> (model, assembly level, etc.) as df0: but *much* quieter than df0: was
> even before I changed the timer jumper!  Oh well ...

	Life is strange...

-- 
George Robbins - now working for,	uucp: {ihnp4|rutgers|allegra}!cbmvax!grr
but no way officially representing	arpa: out to lunch...
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)