Path: utzoo!utgpu!water!watmath!uunet!cbmvax!ditto
From: ditto@cbmvax.UUCP (Michael Ditto)
Newsgroups: unix-pc.general
Subject: Re: 1M to 2M revisited...
Summary: Two cuts & jumpers also needed
Keywords: unixpc homebrew ram upgrade
Message-ID: <4389@cbmvax.UUCP>
Date: 1 Aug 88 19:40:44 GMT
References: <546@bacchus> <8570002@eecs.nwu.edu> <574@bacchus.UUCP>
Sender: ditto@cbmvax.UUCP
Reply-To: ford@kenobi.cts.com (Michael Ditto)
Organization: Commodore Technology, West Chester, PA
Lines: 36

In article <8570002@eecs.nwu.edu> morrison@eecs.nwu.edu (Vance Morrison) writes:
>I have some friendly advice for those interested in upgrading the
>motherboard ram.  It is not as easy as plugging in the ram chips.
  [ ... lists some other things that are required ... ]

Then, in <574@bacchus.UUCP> darren@bacchus.UUCP (Darren Friedlein) writes:
>I've done all this (4 multiplexers, all the chips, a capacitor on each
>chip, the resitor packs and set the jumpers like I was told (same as
>1M in 4 banks).  Still doesn't work.  Anyone know what's missing?

I've upgraded a 1Meg 7300 to 2Meg, so I know it's possible.  I didn't
have to change the jumpers, since they specify chip size (64K vs. 256K).
I DID have to cut two traces and jumper them somewhere else.
Unfortunately, I didn't write down what the changes were, and I don't
have my hardware manual handy; but they were related to address decoding
and selecting one bank vs. the other.  I'll try to get the details and
post them soon.

I feel guilty about posting this teaser ("I've done it, but I'm not
gonna tell you how, nyah nyah" :-) because I did exactly the same thing
about 5 months ago.  The thing I was waiting for then was to make the
same mod to a second machine and take careful notes so that I could tell
you all about it.  Well, I never got around to it (and no longer have
access to that 7300 or the one I hacked), so I'll have to study the
schematics again and hopefully I'll remember the exact mod; at the least
I should be able to give some pointers.

Good luck, hardware hackers!

-- 
					-=] Ford [=-

	.		.		(In Real Life: Mike Ditto)
.	    :	       ,		ford@kenobi.cts.com
This space under construction,		...!ucsd!elgar!ford
pardon our dust.			ditto@cbmvax.commodore.com