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From: colas@lemur.inria.fr (Colas  Nahaboo)
Newsgroups: comp.sys.amiga.hardware
Subject: A500 With 1 Mega chip Ram... Here it is!
Message-ID: <10380@mirsa.inria.fr>
Date: 6 Mar 91 14:41:37 GMT
Sender: news@mirsa.inria.fr
Organization: Koala Project, Bull Research France
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Nntp-Posting-Host: lemur.inria.fr

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.