Fault Diagnosis And Repair - Sinclair ZX Printer Service Manual

The following table is intended as a general guide to the diagnosis
and rectification
considerable usage of the printer.
FAULT
1. Poor print quality:
(a) Vertical zig-zag
usual ly worse on
right-hand side.
(b) Horizontal lines
unevenly spaced.
(c) Print fading out
over part of line
(d) 'Noisy' Printin5-
2. No p r i n t :
SECTION 3

FAULT DIAGNOSIS AND REPAIR

of most of the
POSSIBLE CAUSE
(a) Worn belt.
(b) Worn belt.
(c) Dirt on conductor
strip in top
cover.
<d) W Excessive
( i i ) I n s u f f i c i e n t
(a) If print is all
b l a c k , check TR4.
(b) If no image, check
that white wire
is connected to
conductor strip.
(c) Dirt on photo-
diode and/or LED.
{d} Defective photo-
diode and/or LED.
3.1
faults which may occur after
(a) Fit new belt.
(b) Fit new belt.
(c) Clean and
(d)
gain on TR5.
signal from
encoder.
(a) If defective,
( b ) Connect white wire
(c) Clean photodiode
(d) Fit new photodiode
REMEDY
lubricate
conductor strip -
use El ectrolube.
/^ Fit ZTX551 in
place of
ZTX550
( i i ) F i t n e w ULA.
change TR4.
to conductor strip
and check 50V is
present on strip.
and/or LED.
and/or LED.