Everything You Always Wanted To Know
But Were Too Polite To Ask

Amiga Technical References

For installation 8372A or 8375 Agnus in an Amiga 500:

• Torx T15 Screwdriver or a flathead small enough to fit
• Small jewellers flathead screwdriver OR an exacto knife
• A PLCC chip extractor OR a small flathead screwdriver and a lot of patience
• An 8372A Agnus or 8375 Agnus
• A solder iron and some solder
• These instructions printed out since your machine will hopefully be turned off at the time

• Turn everything off.
• Unplug everything from the machine
• Turn the machine over and remove the 6 T15 screws around the edges.
• Turn the machine right side up now and lift off the cover
• Unplug the keyboard from inside the metal shielding and lift out the keyboard
• Lift the tabs up for the metal shielding and unscrew the four screws holding it down
• Pull out the shielding
• Now exposed is your Amiga 500 motherboard. Hopefully this is a REV 5 or 6 motherboard. Find this out by looking at the inscription just above the trapdoor expansion.
• If it's a REV4, forget it. It's too much of a pain in the ass to trace the solder points from the 68000 and out.
• Look at the Agnus chip and determine it's model number. If it's an 8372A or 8375 already, skip down past the replacing and inserting the Agnus. (down 2 points)
• If the chip is an 8370, then this is what you want to replace. You can remove it with your chip puller or screwdriver. If using a screwdriver TAKE YOUR TIME! If the socket cracks, the chip will most likely not be able to make contact with all the pins and then not work. So be careful!
• Insert 8372A or 8375 Agnus. You MUST match up pin 1 on the chip with pin 1 on the socket/board. The chip has a dimple along one side that signifies pin 1 and the motherboard will have a 1 on it and in some cases the socket will have a dimple in it too. Match them! VERY IMPORTANT!
• Over between the 68000 chip (the big one on the left) and the Kickstart ROM (the smaller one beside the 68000) will be a label for the jumper trace JP2. You have to jump this pad to the opposite position.
• Get that exacto knife or small screwdriver and scrape away the trace that's connecting the bottom and the centre pads. BE CAREFUL NOT TO SCRATCH OUT ANYTHING ELSE!
• If you have an ADRAM 540 skip down to the ADRAM section. If you have a BASEBOARD, I have no idea how to get those to work and you would be better off contacting Expansion Systems.
• Solder the top and the centre pads together. CAREFUL NOT TO SOLDER ANYTHING ELSE TOGETHER!
• If you have a multitester around, use it to make sure you have not accidentally left anything that should not be there.
• If you have a REV5 A500 motherboard you are going to have to scrape another trace out, but it's not labelled. If you have a REV6A then no problems, it's labelled JP7A beside the trapdoor expansion. Simply cut it.
• On REV5's, this is what you do. The trapdoor expansion (right side of the machine where your 512k RAM expansion plugs in) has some traces directly to the left of it. Counting DOWN from the TOP, count DOWN 8 (eight) pins on the trapdoor expansion, look directly left. You will see a solder point on the motherboard and a trace coming out of it going directly UP (towards the back of the machine) You have to cut this trace. You don't have to remove it completely, just break the connection somewhere along that line.
• Cut the trace with your exacto knife or sharp flathead screwdriver.
• Plug the machine back in to see if it works.
• Works? Turn it off and reassemble everything and away you go.

Copyright © 2000 Amiga Auckland Inc. All rights reserved.
Revised: June 16, 2005.