Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!zaphod.mps.ohio-state.edu!usc!apple!coherent!dplatt
From: dplatt@coherent.com (Dave Platt)
Newsgroups: comp.sys.mac.hardware
Subject: Re: MacDemon, get they gone
Keywords: keyboard, power
Message-ID: <40846@improper.coherent.com>
Date: 3 Dec 89 02:41:28 GMT
References: <2670@unisoft.UUCP>
Reply-To: dplatt@improper (Dave Platt)
Distribution: usa
Organization: Coherent Thought Inc., Palo Alto CA
Lines: 49

In article <2670@unisoft.UUCP> cander@unisoft.UUCP (Charles Anderson) writes:
> I came home from dinner the other night to find my Mac II running.  My
> immediate conclusion was that I had left it on for a few days since the
> last time I had used it.  So I shut it down from the Finder menu only
> to have it restart as soon as the power went off.  So I yanked the ADB
> cord out of the extended keyboard and shut it down again.  This time it
> stayed down.
> 
> My first idea was that it was related to the high humidiy we had with
> the rain on that day.  My hypothesis was that there was a bunch of
> moisture shorting the power key in the keyboard.  Since then it's been
> very dry, but the Mac continues to restart itself, usually taking a few
> minutes or an hour before restarting.
> 
> Does anyone have any ideas on how to exocise this evil presence from my
> system?

I had this same problem... although the guilty device was a Kensington
Turbo Trackball.  Your conclusion about humidity is correct... it takes
very little current-leakage across the PC-board traces to trigger the
"Power on!" detector in the Mac II.  Apparently the power-on circuit
in the keyboard is designed to draw very little current... thus ensuring
that the lithium battery in the Mac II isn't run down too quickly.

I fixed my trackball by drying it out in the sun, opening it up, noting
where the power-on trace ran across the PC board (it went from the in-port
to the out-port, and wasn't connected to any circuitry in the trackball),
figuring out where the short-circuit was occurring (pressing my finger
firmly to the traces was enough to make the Mac boot!), and insulating
the traces with a dab of fingernail polish.   The problem went away
and has not recurred.

If you prefer a slightly more high-tech solution than fingernail polish,
you could probably buy a can of silicone- or urethane-based "conformal
coating"... an aerosol spray designed specifically for sealing PC boards
and components against moisture and contamination.

With fingernail polish, you should try to moisture-seal the PC-board
solder contacts of the power-on switch, the contacts for the ADB
connectors, and the PC-board trace which handles the power-on signal.
With an aerosol conformal coating, you could probably spray the whole
solder-side of the PC board (enough to coat, not enough to drip and
run).

-- 
Dave Platt                                             VOICE: (415) 493-8805
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