The Power board takes electric current at 240 volts and converts it into the various voltages to run the screen tube (CRT), drives, printer, keyboard and all electronic circuits The CPU board contains the Central Processing Unit (CPU) which is a Zilog Z80a, memory banks and controller chips for the drives, printer, keyboard and screen.
The power board supplies power to the CPU board, and through the CPU board to the drives, printer and keyboard via the controller chips. The CPU board then passes back information to run the screen and supplies video memory.
Common problems which affect the PCW are listed below with the probable diagnosis.
Screen does not light up when PCW is switched on
Check whether lights are on in drive(s). If not there is a total power failure.
Check fuse in mains plug; if broken replace with 3 or 5 Amp fuse. Check fuse
on power board; replace if necessary with another of the correct specification.
If lights are on in drive(s) it could be a partial failure of the power board or the CPU board. In very rare cases it could be a faulty screen (CRT)
Screen lights up but PCW fails to start when disc is placed in A: drive
Disc may be corrupted; retry with other discs. If this fails it may be a drive
fault or a fault on the CPU board; odds are heavily that it's a drive fault.
If the PCW tries to start with horizontal lines appearing on screen it is a
drive fault. If nothing appears on screen but after a minute or so the machine
emits 3 or 4 beeps it's most probably a drive fault; the beeps indicate that
the CPU board is working OK.
PCW starts OK but error messages appear on screen or machine behaves erratically. The most likely cause is a faulty drive, but first make sure that it's not a software fault. Persistent failure to format or verify discs could be a faulty batch of discs; there are some poor CF2 discs about, even new ones. If possible stick to well-known makes such as Amsoft, Maxell and Panasonic. Software faults can sometimes be difficult to diagnose, but if the same faults persist with different programs entirely then it's probably a faulty drive.
Machine boots Ok but then odd characters appear at the A> prompt or machine
beeps constantly. Keyboard does not respond.
Keyboard fault. Check that the keyboard is plugged in properly. If so the fault
probably lies in the keyboard connecting cable; a broken wire perhaps. Check
with a continuuity tester. If the machine has been opened the fault may be in
the connection between keyboard socket and CPU board.
Printer doesn't work
You may get the message "No Printer". Switch the machine off and check the printer
connections by unplugging and replugging a couple of times. If possible try
another printer or try the printer on another machine. Possible faults are failure
of the 24-volt supply, a faulty printer controller on the CPU board or a faulty
PC board on the printer.
Dot Matrix Printer. makes a line through text
Probably a fault on the printing head. A white line indicates that a pin is
sticking in and never makes contact with the paper, a black line indicates that
a pin is sticking out, making contact with the paper all the time.
Daisywheel printer PCW9512, PcW9512+ Printer behaves normally except that
it prints faintly or not at all.
Usually due to fractured armature. Move carriage to left side. Between the electric
coil and the guide rod, the armature is the oddly shaped part which goes in
and out under the influence of the coil and operates the hammer mechanism. Check
whether there is a crack (you may need a magnifying glass) in the side, probably
near one of the holes in the moulding. If so a new armature must be fitted as
it cannot be repaired.
These are a selection of the most common faults found on PCWs. They can be remedied with the correct spare part by anybody with a little patience, a minimum of tools and the full instructions that I can supply. Do not remove the back from the machine without observing proper safety precautions; extremely high voltages are within. Also unless you are an electronics wizard and have the necessary equipment and knowledge, it is not worth attempting to repair power boards or CPU boards; fit a replacement complete; it's more cost-effective. If your particular problem is not mentioned or you need more information E-Mail me.
Ron King
e-Mail address ...... ron@king27.freeserve.co.uk