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- Path: sparky!uunet!munnari.oz.au!comp.vuw.ac.nz!canterbury.ac.nz!equinox.gen.nz!equinox!bignode!pete
- From: pete@bignode.equinox.gen.nz (Pete Moore)
- Subject: Re: Installing Fatter Agnus (Me too!)
- Newsgroups: comp.sys.amiga.hardware
- References: <168BED4C.WALLY@UKCC.UKY.EDU>
- Organization: Equinox Networks
- Reply-To: pete@bignode.equinox.gen.nz
- X-Newsreader: TIN [version 1.1 PL8]
- Message-ID: <pete.03ii@bignode.equinox.gen.nz>
- Date: 16 Dec 92 13:00:28 +1200
- Organization: Equinox Networks
- Lines: 70
-
- WALLY@UKCC.UKY.EDU wrote:
-
- >I have an AMiga 500 with the regular Agnus, and I would too like to replace
- >it with the Fatter Agnus... I have a revision 5 motherboard, and would
- >also like to know what else needs to be done to get 1 meg of chip ram.
- >
- >I tried swapping my agnus with a fatter agnus once before, but could not
- >get my machine to work at all. (I posted, but got no responses.)
-
- This is what I used (I've lost the name of the helpful person who posted it
- originally). Step 4 is probably the trickiest bit - let me know if you
- have trouble locating the _EXRAM line, and I'll send an ASCII diagram.
-
- -= Installing the 8372a to Revision 5 A500's =-
-
- 1. Remove the 8371 from its socket. If you are an NTSC user who does not wish
- to use the PAL mode, go to step 3.
- 2. Pin 41 of the new Agnus controls whether the machine starts up in PAL or
- NTSC modes. When it is tied low (to ground), the machine boots in NTSC mode.
- When the line is tied high or left floating (ie unconnected), it boots into
- PAL mode. On the Rev. 5 board, pin 41 is connected to ground by tracks on BOTH
- sides of the board, making it virtually impossible to cut the track without
- desoldering the socket. This means if you just plug in the new Agnus, you will
- be locked in NTSC mode !! There are a couple of ways to go about circumventing
- this problem; I will detail here the one I undertook on my own Rev. 5 board. I
- will assume you want to install some sort of switch to toggle PAL/NTSC mode.
- If you only want to run in PAL mode, you can simply bend out pin 41 of the
- Agnus socket (don't bend the pin on the chip) to prevent it from making
- contact with Agnus. If you do this, proceed to step 3. Otherwise, get yourself
- an SPDT or SPST toggle switch and two lengths of telephone (or other thin,
- stiff single-core wire). Solder wires to the switch :
-
- +---+
- To a convenient ground--+-o | BACK VIEW OF SWITCH
- +--------+-o | When held as shown, UP=PAL, DOWN=NTSC.
- | | o |
- | +---+
- Uninsulated --> | | <-- This side is insulated
- \-/ <-- Fold the wire thru 180 degrees
-
- 3. Insert the new Agnus. If installing the switch, you should now poke the
- loose end of wire (see above) from the switch into pin 41 of the socket so
- that the bare copper side touches the pin on the chip and the insulated side
- touches the pin on the socket.
-
- 4. If you wish to install a memory mode switch, go to step 5. Otherwise,
- locate JP2 (between 68000 and ROM). This consists of three pads. The center
- and lower pads are joined by a thin track. Cut this track and place a drop of
- solder between the center and upper pads. Now locate the _EXRAM line coming
- from the A501 port (it comes from pin #32 and runs on the upper side of the
- motherboard parallel to the A501 connector). Cut this line. You have now
- finished installation.
-
- 5. Complicated. Locate JP2 and cut the track which joins the center and lower
- pads. Locate the _EXRAM line from the A501 port (see step 4) and cut the
- track. Solder wires to all three pads of JP2 and one wire to either side of
- the gap you cut in the _EXRAM track. Wire a DPDT switch as follows :
-
- +-----+ BACK VIEW OF SWITCH
- Upper pad of JP2 --+-o o | When held as shown, UP=512K CHIP, DOWN=1M CHIP
- Center pad of JP2 -+-o o-+- To one side of the gap in the _EXRAM track
- Lower pad of JP2 --+-o o-+- To the other side of the gap
- +-----+
- You have now completed installation.
- --
- +------------------- pete@bignode.equinox.gen.nz -------------------+
- | The effort to understand the universe is one of the very few things |
- | that lifts human life above the level of farce, and gives it some |
- | of the grace of tragedy - Steven Weinberg |
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