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From: srb@ccvaxa.UUCP
Newsgroups: net.micro.mac
Subject: Re: Mac hardware problem
Message-ID: <2900009@ccvaxa>
Date: Thu, 7-Nov-85 23:37:00 EST
Article-I.D.: ccvaxa.2900009
Posted: Thu Nov  7 23:37:00 1985
Date-Received: Sun, 10-Nov-85 07:25:38 EST
References: <3198@mhuxd.UUCP>
Lines: 37
Nf-ID: #R:mhuxd.UUCP:-319800:ccvaxa:2900009:000:1570
Nf-From: ccvaxa.UUCP!srb    Nov  7 22:37:00 1985


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Someone who had done a DDJ conversion was asking about how to fix
shorts under a socket without removing the whole row.

One aid is to use a high-precision ohmmeter (Fluke 4 1/2 digit
multifunction meter works), i.e., one which will discern a
milliohm or so.  You can locate a short to within an inch or so
on 10 mil traces like the Mac's.  We used to do it all the time
on some boards we made.

The easiest way to fix open/short problems under a socket is to
use sockets with "open entry" pins.  After being soldered into
the board, the plastic shells of such sockets can simply be pulled
off the pins (gently!) with a pair of pliers, leaving all 16 pins
sitting firmly soldered into the board.  Then put the shell back on
(gently!) after the problem is fixed.  You can generally spot such
sockets by simply turning them over and looking at their undersides.
(To be really sure, grab a pin with a pair of pliers and try to
pull it out.  It should come out and go back in relatively easily.)

It is non-trivial to solder a replacement pin into the PC board straight
enough to align correctly with the shell, without the shell in place.
Don't try.  Just put the pin into the shell, re-insert the shell/pin,
and resolder.

I did the Levco upgrade, and when finished with both the
removal and the socket-soldering steps, spent a half hour
with a 8x (slide loupe) magnifier examining holes, traces, etc.
Time well spent.  Found a couple of potential bridges.
The upgraded Mac worked first time.

Steve Bunch.   ..!uiucdcs!ccvaxa!srb
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