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From: stevel@dartvax.UUCP
Newsgroups: comp.sys.mac
Subject: Re: new ROMs and 3rd party upgrades
Message-ID: <5977@dartvax.UUCP>
Date: Thu, 9-Apr-87 11:42:18 EST
Article-I.D.: dartvax.5977
Posted: Thu Apr  9 11:42:18 1987
Date-Received: Sat, 11-Apr-87 14:56:47 EST
References: <127200004@inmet> <2969@sdcsvax.UCSD.EDU>
Reply-To: stevel@dartvax.UUCP (Steve Ligett)
Organization: Dartmouth College, Hanover, NH
Lines: 68

If you have a third party upgrade that won't work with a
particular set of roms, the cause is likely to be that the
upgrade doesn't have pullups on the added address lines.  Some
roms may be fussy about the levels.  This problem can exist with
the Dr. Dobbs upgrade.  I don't know of it causing problems, but
it might.  It's simple enough to duplicate the Apple 512k
circuitry exactly.  On upgrades I do, don't quite duplicate
Apple's circuitry.  Let me try to describe: (I'll assume that
you know the basics of the upgrade - where to put the 253, and
about the row of pads near it, since I do it by instinct now,
and don't remember the coordinates.)

pin 1 - jumper to ground (pin 8).
pin 2 - solder to pin 2 below it.
pins 3,4 - tie to +5, pin 16.  I use a bare wire so I can solder
the pullups from pins 5, 6 to it.
pins 5,6 - a 2.2k pullup from each to the wire mentioned above,
and a wire to pads 6, 3 (!maybe!) in the nearby group.
pin 7 - connect with a 47 ohm resistor to pad 2 in the group.
pins 8, 9 solder to pins 8, 9 below
pins 10,11,12,13 - tie to +5.
pin 14 - solder to pin 14, below.
pin 15 - tie to +5.  I solder a bare wire across 10, 11, 12, 13,
and 15 to pin 16.
pin 16 - solder to pin 16 (+5) below.

Don't forget to cut the jumper from pad 1 to 2 in the group.
Hmmm, the diagram below is almost understandable to me.  If
you use it with the text above, you might be able to do an
upgrade.
       +--------------+
       |  --------    |
       +==1 +++--*--+ |
          * ||| 15==+ |
          3-+RR  *  | |
          4-+|| 13==+ |
     +--==5--+| 12==+ |
     |+-==6---+ 11==+ |
     ||+==7     10==+ |
     ||| +*      *    |
     ||| |--------    |
     ||R +------------+
     |||
     |||   O
     ||+---*
     |=----*
     |     O
     |     O
     +-----*
           O
Warning - This may have errors.
Apology - I didn't mean to write this much.
Disclaimer - It's not my fault if you break your Mac.  I've done
a couple hundred upgrades this way, and only one didn't work.
But on that one, I hadn't tested the board before doing the
upgrade, so maybe it didn't work as a 128k.  (some day I'll have
to get back to that board...)








-- 
     Steve Ligett  stevel@dartmouth.edu  or
(astrovax cornell decvax harvard ihnp4 linus true)!dartvax!stevel