Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!lll-winken!uwm.edu!rutgers!cbmvax!raible
From: raible@cbmvax.commodore.com (Bob Raible - LSI Design)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: A500 With 1 Mega chip Ram... Here it is!
Message-ID: <19575@cbmvax.commodore.com>
Date: 6 Mar 91 19:58:01 GMT
References: <10380@mirsa.inria.fr>
Reply-To: raible@cbmvax.commodore.com (Bob Raible - LSI Design)
Organization: Commodore, West Chester, PA
Lines: 86

In article <10380@mirsa.inria.fr> colas@lemur.inria.fr (Colas  Nahaboo) writes:
>After querying the net, I finally got the info I wanted from Darrell Grainger!
>Here it is:
>
>WARNING: this WILL void your warranty, and you could seriously damage your amiga
>if you don't know what you are doing. Do this at your own risks!
>Look at the schematics at the end of your A500 user manual, you will clearly see
>of what lines Darrell speaks.
>
>------- Forwarded Message
>
>From: darrell@comcorp.uucp
>Subject: Re: Updating the A2000
>Date: 	Fri, 1 Mar 1991 11:09:12 -0500
>
> To get the Amiga 500 to recognise the A501 (or equivalent) memory as CHIP
>memory, you need the 8372A Agnus chip. The 8370 Agnus is NTSC and only
>addresses 512K of memory (the 512K on the motherboard). The 8371 Agnus is
>PAL and only addresses 512K of memory. The 88372A can switch between NTSC
>and PAL and addresses 1M of memory (the 512K on the motherboard and the 
>512K in the trapdoor). The 8370/8371 Agnus does not have enough address lines
>to physically address 1M of memory. The 8372A has enough address lines to
>handle 1M of memory by the A501 memory must be reconfigured. This is done by
>changing some address lines between the Agnus, 68000 and Gary chips.
> 
> You need to change two things. First, pin 32 of the Gary is connected to
>ground. This connection must be cut. Looking at the motherboard, right near
>the A501 connector (CNX) you will see a trace from front to back of the machine
>and ends near the CNX (actually it goes through a hole on the motherboard to
>the underside of the board). the trace is about 3 cm long. Cut this trace
>with a knife (don't cut too deep, just enough to break the trace). To confirm
>you have the right trace try testing the resistance between the end of the
>trace and pin 32 of the Gary chip. There should be little or no resistance.
>Also, once you cut the trace you can test the resistance to see if it was a 
>good cut. The resistance should be 100%.
> 
> Second, pin 59 of the Agnus must be changed. Right now this pin is connected
>to pin 39 on the Gary and pin 52 on the 68000. On your revision motherboard
>there should be a jumper between the Kickstart chip and the 68000 (kickstart
>is part number 315093-01 or 315093-02). This jumper is a trace in three parts
>(three little squares). The first and second square are connected and the third
>square is off by itself. What you need todo is cut the trace between square
>one and two then solder together square two and three. What follows is a 
>basis diagram of what I just described.
>
> Argh... forget the diagram... you should be able to figure it out from the
>description.
>
> If you cannot find the traces I am talking about then here is how you do it
>on boards that do not have the jumper between Kickstart and 68000.
> 
> Cut the trace going from pin 59 on the Agnus to pin 52 on the 68000 as close 
>to the Agnus as possible. Use an ohm meter to find the trace that connects
>these two pins together. On the bottom of the motherboard find pin 59 of the
>Agnus (this is the easiest place the find the pin and best place to put a
>jumper wire). From the pin 59 of the Agnus socket jumper over to pin 47 of
>the 68000. Your done.
> 
> Please be careful and remember that this voids warrantee. If you don't know
>how is solder you can do some major damage and I will not be held responsible.
>The Amiga 500 is a multilayer board so don't use a soldering gun; use a proper
>electronic soldering iron.
> 
> Be careful of static electricity too.
>
>Darrell Grainger
>
>
>------- End of Forwarded Message
>
>
>-- 
>Colas Nahaboo, colas@sa.inria.fr, Bull Research, Koala Project, GWM X11 WM
>Phone:(33) 93.65.77.70(.66 Fax), INRIA, B.P.109 - 06561 Valbonne Cedex, FRANCE.


Correction: the part you require is the vanilla 8372. The 8372A is the
A3000 version with a different bondout. I believe that some A500 already
have this chip on the later revs of the mother board. Those users do not
need to obtain a new AGNUS(happy birthday :3) ). The 8372 is bonded out
for the 1MEG chip RAM you seek. As for the rest of your posting your on
your own, but I didn't see any other errors. 

I am not in a position to endorse the above course of action, but I did
wish to correct an obvious error. To all you hackers out there GOOD
LUCK!