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From: straka@ihlpf.UUCP
Newsgroups: comp.sys.mac
Subject: Re: Repairing failed video on Mac
Message-ID: <1263@ihlpf.ATT.COM>
Date: Fri, 20-Mar-87 09:48:38 EST
Article-I.D.: ihlpf.1263
Posted: Fri Mar 20 09:48:38 1987
Date-Received: Sun, 22-Mar-87 19:11:54 EST
References: <1354@tekig4.TEK.COM>
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 30
Summary: Working on your Mac (and SAFETY warning) (was failed video)

Yes, this procedure seems to be common for the Mac.  The tech who
installed my disk and ROM upgrade resoldered the harness connections on
my analog board (for good measure).  They evidently crystallize with
time due to the heat factor.

I would like to add that it is very important not to fart around with
the 2nd anode potential which goes to the CRT (the big wire that goes on
the side).  It can hold a charge for hours (days?), and be quite a
shock.  Easy solution: ground a screwdriver with a test lead (eg with
alligator clips) to a major metallic part of the Mac chassis; then
gently insert the grounded screwdriver under the rubber cap until it
shorts (don't touch the metal part of the screwdriver, or you'll still
get zapped).  This is standard procedure when working with ANY CRTs in
the consumer field and hasn't ever hurt any circuitry that *I* am aware
of.  Note that a lesser, secondary charge can develop and give a lesser,
although still substantial shock.  Redo the above just before touching
anything close to that second anode.

This is serious stuff, and can cause DEATH if done in an incorrect
manner by someone naiive to electrical circuits.  Be CAREFUL if you
touch these kinds of things at all!!

I have worked with this kind of stuff on and off for 20 years, and still
feel nervous when working around ANY high voltage (I got zapped by a
color TV 2nd anode once in high school).  I like living.

Are you ALL clear on this? (I hope so; I think I just beat it to death!)

-- 
Rich Straka     ihnp4!ihlpf!straka