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From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: 8520's again... (was: My clock is counting up fast!!!)
Keywords: 8520
Message-ID: <21201@cbmvax.commodore.com>
Date: 3 May 91 06:27:20 GMT
References: <1991May1.112820.22292@uservx.afwl.af.mil> <1991May2.154402.1259@daffy.cs.wisc.edu>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 35

In article <1991May2.154402.1259@daffy.cs.wisc.edu> pochron@cat30.cs.wisc.edu (David Pochron) writes:

>Now, on a slightly different subject...

>A while ago I posted about how I fixed my clock problem by replacing the
>8520's with older ones from an A1000, but got no response.  I'll try again...

The older 8520s have a significantly lower output current on the "B" port,
and there are some internal pullups removed.  The output strengths were
increased in order to eliminate some problems that had been seen with printers
during the A1000 days.  While I think the old 8520s will function in an A2000
or A500, you don't want to put a new one in the A1000, some lines will float.

>I tried several 8520A-1's in my 2000 and none would fix the problem of my 
>haywire clock, but, when I use the older 8520RS' chips from the 1000, the 
>A2630 card likes them just fine.

Whatever your clock is doing, it sounds to me like your real problem is with
the TICK clock coming from the power supply.  I take it that your run-time
clock isn't acting reasonable.  That can be an 8520 failure, I had one die on
me this way once.  It can also be a problem with the TICK input to the 8520.
You can change J300 to use the VSYNC* line instead as a timebase, and see if
the newer 8520 still shows a problem.  It's very possible that, assuming
something is different on your TICK line, it's a marginal thing that just 
happens to be seen by one series of 8520 and not by the other.  While the old
part shouldn't be a problem, other than on long printer cables (and it may be a
tad easier to zap), it's usually a good idea to solve a problem rather than just
work around it, when you have the chance.

>          David M. Pochron   | Transparent DWV pipe:  For the man who wants to

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
      "That's me in the corner, that's me in the spotlight" -R.E.M.