Amiga A3640 CPU Board Repair

To be able to make the suggested changes to the A3640 CPU Daughterboard, it is necessary to remove it from the A4000 motherboard. Care must be taken at all stages to ensure success and minimize the risk of damage.

First, remove the power cord from the back of the Amiga 4000. This is to prevent accidentally applying power while working on the computer, and to prevent accidental electrocution while you have your hands down inside the computer.

Now, remove the two cover screws on the back of the Amiga. The case will slide (with some difficulty around the mouse ports) back, allowing you to lift it up and away from the bottom half. You are now able to look and work inside the Amiga.

You need as much room as you can get to be able to get to the A3640, so you need to remove all Zorro or ISA/EISA plug-in cards. If you have not installed any, then this part is done.

The harddrive is held in place by a bracket. This bracket has four screws that mount it to the Amiga. Remove the four screws, and move the harddrive out of the way.

Now, remove the Zorro-III bracket. It is held down with two screws, one in front and one in back. The Zorro-III daughterboard can now be unplugged and set aside.

At this point, if you are experienced, you may be able to remove the CPU daughterboard without any further disassembly. It is tricky, and may result in permanent damage to either the A3640, the motherboard, the connector, or any combination thereof. The safe thing to do is to continue dismantling the A4000.

Remove the front faceplate. This is plastic and snaps onto the chassis with plastic latches. Be very careful getting this faceplate off. It is very easy to break plastic, especially when you don't intend to. The keylock switch, harddrive LED, and power LED are attached to the motherboard and their wires need to be unplugged. Make a list of which color wires plug into which connector. It makes reassembly much easier.

Unscrew the A4000 motherboard from the chassis. There are almost a dozen screws that hold it down, so take your time and carefully locate each one. Don't forget to remove the two screws that hold the serial connector to the back side of the computer.

It should now be possible to remove the A4000 motherboard and the A3640 CPU Daughterboard from the chassis. With the motherboard out of the chassis, you will now have more room to carefully pry the A3640 off. Be gentle. Things like this break easy. There are three or four standoffs under the A3640. It is not important if they stay attached to the motherboard or the daughterboard when the two are seperated. The important thing is to not lose them.