SAFETY
Very high voltages are generated inside the casing, around the cathode ray tube
and power board. 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 may 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 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 enclosed in a metal shield 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 plugs and sockets have been colour-coded, or marked or will only go on one way.
Unplug all cables which connect the upper and lower case. Smaller 4 or 5 pin 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.
Where there are larger type plugs they are often rather tight and should be prised apart with a wide screwdriver blade or something similar. Don't try to use brute strength or you may do some damage. A couple of two-pin plugs are identified on the printed circuit board where the colours of the wires are printed.
Finally disconnect all the black and yellow/green wires by unscrewing from the sides of the power board, casing etc. There are quite a lot of these as they link all metal parts together to help, together with the metal shields, to reduce radio interference from the computer.
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 by hinging it down to the table, checking that no connecting wires remain.
With the lower casing on the table the drive(s) can be accessed. Remove four screws from each drive and unplug the 26-way cable from the drive, first noting which way the plug is fitted to the drive (there is a coloured wire on one side of the cable).
Fitting the replacement drive is done by reversing the dismantling procedure. Connect the drive and screw it in place. The 26-way cable carries the power supply as well as data and instructions so make sure it's connected properly and the right way round. Reassemble the casing with the four screws and replace all the plugs and wires. Have a good look around before replacing the back for testing. Take your time and make sure everything is OK. Don't try to force anything. The back can be difficult to replace sometimes but patience will be rewarded. It only remains to plug in the keyboard and try the machine. Always use a spare disc if available to test a drive, never a valued one, or at least open the 'write protect' hole. It'll probably be OK, but .............
What if it doesn't work? Unlikely, if you've followed the above instructions.
The most likely cause of trouble is faulty connection of the cable, so switch off, unplug the cable and carefully plug it in again making sure that all pins are connected- it's easy to miss out a couple of pins or even a whole row. I don't know whether the drive can be damaged by connecting the plug wrongly; as the power supply is only 5 volts and the electronic circuit also uses 5 volts it is unlikely but it is not recommended so try to avoid it. If the light comes on in the drive and the motor runs the plug is fitted correctly.
Another possible cause of error is incorrect configuration of the drive. Drives are configured A: or B: by the position of a "jumper" at the rear of the drive. Drives ordered from me will be configured A: or B: as ordered but are not interchangeable unless reconfigured.
Failing this, the fault may not be with the drive but in the machine itself. If this is suspected then the drive should be returned for retesting; if it is still OK then the problem must lie within the machine.
Switch off and remove the wall plug before touching anything, unless you are experienced. NEVER DISCONNECT OR RECONNECT ANYTHING WITH THE POWER ON. This can damage the machine or you or both.
Ron King
e-Mail address....... ron@king27.freeserve.co.uk