The dot-matrix printer of the PCW8256 and PCW8512 is designed to be absolutely compatible with those machines. It cannot be used with other computers, because it is integrated with the machine and needs circuitry on the CPU board to function. It is connected to the PCW by a 34-way data cable and a 24 volt supply for the motors and print head. The data cable also carries 5 volts for the circuit board.
Many other printers can be used with the PCW through a parallel interface connected to the expansion port, but they may have slight problems, such as being unable to print some obscure characters, or may have paper loading problems, or may be difficult to stop in emergency. Despite it's shortcomings in quality of printing the 'built-in' dot matrix is very easy to use and is OK for most jobs.
The printer is quite rugged but like most pieces of equipment has it's typical faults.
The PCW8256/8512 dot matrix printers can be divided into two broad groups,
depending upon the type of print head fitted, although there are detail differences
within the groups.
One type of print head plugs into the head carrier. It can be be identified
by the word HOT moulded into it's top face. You can sometimes remove this head
by gripping the side between thumb and forefinger and pulling straight up. If
this doesn't work, look for the split-line on the side, about 12mm down from
the top and insert a fine blade to start it.
The other type, usually distinguished by a silver label on it's top face will
not unplug but can be freed from the head carrier by removing the bright metal
clip at it's base. It is connected to the plastic cable which conducts signals
to the pins. This cable can be easily unplugged from the carrier but is difficult
to replace, so don't remove it unless it's necessary.
Stuck Pins
Both types of head suffer from the same fault; if a pin does not operate
there will be, in effect, a white line across the page. (assuming that the paper
is white, of course). If a pin is stuck out a continuous line will be drawn
across the print.
In the latter case the pin may simply be stuck out by dried ink. Removing the
head as discussed before, give the pin ends a good clean with a toothbrush and
meths, or better still WD40, as this also has lubricating properties. Another
reason for a pin sticking out is if the pin has become bent, maybe by using
a cloth ribbon which has been inked too often and has become baggy. In this
case there is little that can be done.
If a pin is not operating (stuck in) it could still be a case of ink gunge,
but it may be that the tiny solenoid which operates the pin has broken. This
can be checked with a continuuity meter. Both types of head have 11 connections.
The centre, wide one, is 0 volts and common, and nine of the narrow tracks are
5 volt connections to the nine pin solenoids; one is not connected. With one
probe on the wide centre track, check each of the narrow tracks for continuuity.
If nine of the ten check OK all solenoid windings are good. The plug-in type
can be tested directly in this way but it is necessary to unplug the cable from
the head carrier to check. As I said, it is difficult to replace and it is often
easier to remove the whole printer mechanism for easier access; not a big job.
A broken solenoid usually means that the head is scrap unless a solenoid plate
from a similar head with damaged pins can be found.
In extremis, the head can be dismantled to try to straighten pins or repair
other damage, but should only be attempted in a spirit of adventure with a head
that is otherwise not salvageable. Before starting, check that you have three
hands and six fingers, at least, on each hand. A pencil and paper, to make sketches
as you go along is a necessity. A set of small screwdrivers is useful and a
pair of tweezers are invaluable. Some heads are just held together with a spring
clip, others by screws. Try to keep the pins in position; if you take them out
they can take a lot of time and patience to replace.. In each head there are
several types of pins so if you do take them out be sure to place them in a
pattern on a marked sheet of paper so that you know which pin goes where. If
the pins flip out, as they have a nasty habit so to do, don't despair. Their
correct positions can be worked out; it's where a degree in solving Chinese
puzzles is useful.
So much for print heads and their problems, but there are other things which can go wrong
A message on the screen says that there is no printer, or the Save menu doesn't show one.
Switch off the machine, unplug the printer, then plug it back in again.
Do this a few times. Sometimes a slight oxidisation occurs around the pins which
prevents a good connection. If the plug is loose the two rows of pins can be
prised apart a tiny amount to counteract this. If this fails there is probably
a fault in the driver chip on the CPU board or in the PC board inside the printer.
If the printer fails to work check also that the 24 volt supply is OK. Substituting
with another printer can also help to pinpoint the fault.
Paper doesn't feed properly or skews.
When paper is put into the printer and the bail bar pulled back, rollers
at the rear of the platen pinch the paper against the platen whilst the paper
feeds in to the initial printing position (Top of form). When the bail bar is
released it holds the paper against the platen and the rear rollers release
their grip. The major force then which advances the paper is the friction between
paper and platen and this friction is drastically reduced by ink which has dried
on the platen.
The platen should be cleaned occasionally with methylated spirit and a clean
cloth, cotton wool or kitchen paper. Scrub the platen vigorously whilst turning
it, until most of the dried ink deposit is cleaned off. It will take quite a
time and you'll never get it all off but keep going until there is only a little
ink showing on the swab.
The bail bar helps by ensuring that the paper wraps around the platen. It is
held against the platen by a spring at either side. If the platen contacts the
platen more firmly one side than the other suspect a missing spring. These springs
are very hard to see unless the whole mechanism is removed from the casing and
viewed from underneath. If a spring is missing, a replacement can be made using
piano wire purchased from a model-makers shop, using the remaining spring as
a model.
At the front of the platen, where the ribbon runs, is a bright plate which also guides the paper. Sometimes this plate becomes displaced, particularly if continuous address labels have been wound backwards. It is just clipped in position and can be relocated fairly easily with the mechanism out of the casing.
Dismantling the printer 1) Pull off the handwheel 2) Prise off the bail
bar operating wheel 3) Turn the printer upside down and remove 6 screws. 4)
Turn the printer right way up and take off the top cover. 5) Remove the 4 screws
which hold the printer mechanism in place. 6) Lift the mechanism off the locating
pegs and it can be removed entirely from the lower case together with the PC
board.
Needless to say, all this must be done gently, taking particular care when removing
the PC board and noting which way it goes into it's slot and how the cables
are routed.
Note that some of the cable connectors, notably the black ones, are very poor,
and if you are getting electronic problems such as motors not working, printhead
problems which are not covered by earlier notes or sensor problems, check these
connectors.
With the innards removed, the casing can be washed in warm soapy water and the
mechanism brushed clean using a small soft paintbrush.
If you need to dismantle further it easy to see how thing come apart; for example,
the platen can be taken out completely without much hassle, but be careful around
the bail bar mechanism because the plastic connectors on the links are easily
broken. There are spaces for four small roller assemblies behind the platen,
but if your printer has only three, don't worry. I have seen many like this
and they work OK. I expect Amstrad must have been short of these assemblies
at one time, so fitted one less.
Ron King
Andover, UK
Email address.... ron@king27.freeserve.co.uk