This job is easy as long as you take your time and work methodically. There is no delicate work to be done and the only tool you need is a long Philips (crossblade) type screwdriver.
SAFETY
Very high voltages are generated inside the casing, around the cathode ray tube.
Before opening the casing of the computer switch off and leave for a few minutes
to allow static charges to leach away. Then remove the electric plug from the
mains socket. Even then, high voltage static charges will remain for a time
which can administer a shock. Whilst such shocks are unlikely to cause injury
they can be unpleasant and are best avoided, so I recommend that the machine
is left for at least an hour, preferably overnight, after disconnection before
removing the casing back.
METHOD
Remove the printer, keyboard and any accessories connected to the expansion
port. leaving the unit bare. Place a folded towel or similar soft cloth on a
working surface and lay the computer face down on it. Remove 6 screws from the
back and sides and place in a safe place. Remove the two small knobs from the
side of the case; they simply pull off. Carefully lift the back off. You may
need to insert a knife blade in the joint to start it, but it should lift off
easily. If not, find out why before proceeding.
Turn the machine right way up and examine it. Just below the tube is the power board, and beneath the power board is the CPU board and drive(s). These latter are screwed to the lower part of the casing which must be separated as a unit from the upper casing in order to access the drive(s).
These machines come in various layouts, so only general instructions can be given. It is recommended that notes and sketches be made whilst dismantling to ensure that all connections are remade correctly. In all cases that I have encountered on this machine plugs and sockets have been colour-coded, or marked or will only go on one way.
Unplug the cables which connect the power board to the CPU board. There are usually two; a white 5-way plug at the RH side and a blue 4-way plug at the LH rear edge. The plugs are usually colour coded and will only assemble one way. They have a security clip which must be held back whilst unplugging. Try to pull on the plug not the wires. They should separate easily; if not find out why. Finally disconnect the black earthing wire by unscrewing from the side of the power board.
Place the monitor face down on the soft cloth again and remove 4 black large-headed screws on the steel angle plates which hold the upper and lower parts of the case together. Carefully separate the lower part, checking that no connecting wires remain. There are lugs on the casing at the front which form a sort of hinge that can make it awkward to separate the casing sometimes, so use a little care here to avoid damaginr the case.
The CPU board can now be clearly seen. Unplug the black 4-way plug to the keyboard socket and cut the tie which secures the cable to the CPU board. Unscrew the two screws which secure the CPU board and draw it back. Unscrew the black earthing wire to the drive; this will free the back cover of the drive which can be removed.Unplug the data and power cables to the drive(s). The 4-way power cable will only go on one way, but make a note of the way in which the data cable goes. Usually the coloured wire goes next to the power connection. The CPU board should now be free of the machine.
Replacing the board is the reverse of the above. Check off the connections as they are made; it is easy to overlook one. The machine can be checked before replacing the back but don't make any revisions without switching off and leaving the machine for a time as described earlier. DON'T PLUG OR UNPLUG ANYTHING WITH THE MACHINE SWITCHED ON or you could do serious damage to the machine.
Ron King
e-Mail address......ron@king27.freeserve.co.uk