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 remove the electric plug from the mains socket. Even then, high voltage static charges will remain for a time which can administer a nasty 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, to allow the static charges to leach away.
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The photo shows a PCW8512 with the back cover removed. The A: and B: drives can be clearly seen together with the CPU and Power boards. If your display rolls or is distorted it can be cured by using the horizontal and vertical holds, both of which are accessible when the back cover is in place. |
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 place in a safe place. 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 so that the drive(s) are nearest to you. Each drive has two connections. The wide (26 line) ribbon cable is the data cable, the small 4-pin connector is the power cable. These connections must be unplugged, but pull on the connectors, never on the cables. The small ones have a plastic clip nearest to you which holds the connector in place; Insert your fingernail or a small blade between clip and connector, pull back the clip a little and the connector will unplug easily. These connectors can only be replaced one way without force, but before removing the data cables check which way round they are connected, and make a note of it. Most models have the blue strip to your left (top of machine) but there are bound to be exceptions.
Just behind the drives is the CPU board which contains the Z80A CPU, the memory chips and much more. This has to be lifted out of the guides at each side and rested back behind the guides against the tube to make room. There is a clip about halfway down the guide on your left. Hold this back with your left thumb and lift the board by the top centre. It should lift easily, if not, investigate, do not use force. The connector for the keyboard may be displaced from it's socket, but this can be replaced in due course.
Remove the 4 screws which hold each drive to be replaced and lift out the drive carefully. Lower the replacement drive into position and secure with the 4 screws.
Replace the CPU board in it's guides, making sure that it is completely home, and that the clip is holding it. Replace the cables, ensuring that they are connected properly; it's easy to miss out some pins on the data cables, even a whole row, as I have discovered.
Have a last look around the innards, check that the mains power cable and the keyboard connector are properly seated in the lower case, then lower the back carefully down making sure that the expansion card and the printer connections feed through their respective holes nicely and that the back fits snugly on to the lower case. Once again, don't try to force it; if it won't go, lift it up and try again. When all is well, replace the 6 screws which secure the back and the job is done. 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 Highly unlikely, if you've followed the above instructions.
The most likely causes of trouble are the power and data connections to the drives. If the drive won't run or the red light doesn't glow, then suspect the power connection. If the machine won't boot then check the data cable(s). Either an A: or B: drive wrongly connected will prevent booting. Unplugging and replugging will sometimes cure a fault. If a drive is connected the wrong way round, it won't damage it, but will obviously prevent it working.
Leaving the back off whilst tracing a fault is safe if you keep well away from the tube side. The drives and CPU board carry a maximum voltage of only 24 volts. But switch off and remove the wall plug before touching anything, unless you are experienced. NEVER DISCONNECT OR RECONNECT A DRIVE WITH THE POWER ON. This can damage the drive and/or the CPU board.
Ron King
e-Mail ........Ron@king27.freeserve.co.uk