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M
G
OTOR AND
EAR
The motor and gear train assembly drives the following:
a) Belt assembly, which produces the printout image
b) Paper feed roller, which moves the paper upwards as printing proceeds
c) Encoding disc, which functions in conjunction with the control electronics PCB to provide the
printout signals to the styli on the belt assembly.
The horizontally mounted motor drives, via bevel gearing, the vertically mounted pulley and wormshaft
which rotates the belt assembly. This wormshaft drives a horizontally mounted wormshaft which, in turn,
drives the paper feed roller assembly. At the lower end of the pulley and wormshaft, a spur gear drives
the encoder disc, both items being mounted within the underside of the base frame.
C
E
ONTROL
LECTRONICS
The control electronics board is mounted on the upper surface of the base frame. In conjunction with the
encoding disc and the LED/photodiode combination, the board provides signals to drive the motor and
the printing system. The PCB is connected to the double-sided edge-connector by a short loom; the PCB-
end of the loom is clamped between the top cover and the base frame when the cover is secured to the
base.
B
F
A
ASE
RAME
SSEMBLY
The base frame assembly comprises the base frame and the base frame insert, both of which are plastic
mouldings. The base frame provides a chassis on which most components are mounted; the base frame
insert is a removable section which fits into the underside of the base frame. The insert contains the lower
bushes for the shafts of the drive and idler pulleys, as well as the mounting for the LED. It is secured to
the base frame by two of the four screws which retain the top cover, and by two shorter screws (see
Figure 3).
P
R
C
APER
EEL
ARRIER
The paper reel carrier assembly consists of a plastic moulding which houses the reel of electro-sensitive
paper, and a spring-loaded pinch roller. The paper is supported in the carrier on two plastic spigotted end-
caps which are inserted into the ends of the tube at the centre of the reel; these end-caps should be
transferred to the new reel when the reel is changed. The spring-loaded pinch roller forces the paper into
contact with the paper feed roller to provide the 'grip' necessary to enable the paper to be fed through
the printer. The complete assembly slides into the base frame, and clips into place; it is released by
pressure being applied to the point marked 'PRESS HERE' on the underside of the carrier.
Normally, the paper feeds through the printer as printing takes place. However, a manually operated
paper feed switch is fitted to enable the paper to be fed through without printing, for example, to provide
a tear-off margin at the end of a print-out. The operating button for this switch protrudes through the top
cover.
6
Sinclair ZX Spectrum Service Manual
Spectrum For Everyone https://spectrumforeveryone.com/
T
A
RAIN
SSEMBLY
B
OARD
A
SSEMBLY
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