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Removing and Replacing a PC104 CPU7 Board

This document applies to 1996 - 2002 M400 and M15 controls which use PC104-bus motherboards.

It is sometimes necessary to remove and replace the CPU7 board, which is plugged into the 104-pin bus connector on the motherboard.

In particular, with newer motherboards (Aaeon PCM-6890 and -6893) you may eventually need to replace the motherboard battery. The following instructions address battery replacement, but could apply to any situation where you need to remove and reinstall the CPU7.


The motherboard is in the console, sandwiched underneath the Centroid CPU7 board.

See here for an example of the Aaeon motherboard.

The battery is just below the PC104 pin bus (where the CPU7 plugs into the motherboard) and left of the Celeron CPU (the device with the aluminum heat sink). It is a common 3V type CR2032 battery.

To get to the battery you have to remove the CPU7 board.

In this situation you can generally remove the CPU7 board without unplugging any of the connections to it: the three or four encoder cables on the bottom edge; the five optical fibers on the left edge; and the jog panel connector just in from the left edge.

Remove the aluminum cover plate (5/16" socket for nylock nuts); remove the four hex standoffs in the corners of the CPU7 board (1/4" socket); and very carefully unplug the CPU7 board.

The CPU7 board is mostly held in place by the 104-pin bus connector, so you want to pull gently all around that connector, gradually working it loose. However, the corners of the board tend to hang up on the threads of the next layer of hex standoffs, so while working the pin bus loose you need to periodically free the corners so the board doesn't get flexed excessively.

Ground your fingers to the frame of the console and/or the hex standoff posts before touching the CPU7 board, to discharge any static.

Once the CPU7 board is free you can let it hang by its cable and fiber connections while you replace the battery.

To reinstall the CPU7, line up the corner holes with the underlying hex standoffs, and gently press it in while working it around slightly until you feel the pins of the PC104 bus connector start to fit in place. Then look between the boards with a flashlight and mirror to verify that all the pins are seating properly: all are going in straight; not off by a row or column; and not impaling any ribbon cables or other obstructions. Once you verify it is going on properly, squeeze the boards together with your fingers over the pin bus. Again, stop periodically to help the corner holes go onto the hex standoffs.

When the board is fully seated, double-check it with the mirror, then reinstall the upper set of hex standoffs and the cover plate. Power up and test.

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Copyright © 2010 Marc Leonard
Last updated 18-Apr-2010 MBL