2.2
Power
Supply
Unit
The unstabilised external power supply unit is a source of some
problems. The design is such that, at minimum input voltage
(215V a.c.) and 1.4A output, the voltage trough should not be less
than 7.0V; at maximum input voltage (265V a.c.) and 60QmA output, the
voltage peak should be less than 13V.
2.3 Initialisation
At switch-on the computer should automatically 'initialise' and
produce a clear screen with the statement
(01982 Sinclair Research Ltd
displayed in the lower left section of the screen. This indicates
that most of the system is working. If the Spectrum does not
initialise,
carry
out the
following
basic
checks.
Basic Checks. It is difficult to be specific in a fault-finding guide
because of the large variety of fault conditions which can occur, but
the following procedure, starting with a table of checks set out in
order
of
priority,
will
however
isolate
the
major
fault
area.
FUNCTION CIRCUIT REF. WAVEFORM/VOLTAGE
Voltage regulator +ve side of C50 +9V d.c. ± 2.0V. At less
input than +7V the regulator may
not operate correctly.
Voltage regulator +ve side of C34 +5V d.c. ± 0.25V - no
output
discernable
ripple.
On-board power supply
outputs:
+5V d.c. IC6 pin 9 +5V d.c. ± 0.25V - no
discernable ripple.
-5V
d.c.
IC6 pin 1 -5V
d.c.
+ 12V
d.c.
IV6 pin 8
+12V d.c.
+ 12VA(to IC14 only) LT end of C52 +12V d.c.
Clock pulses IC1 pin 32 14MHz squarewave at +5V
TR3 base and amplitude,
collector IC2
pin 6
Address and data RT side of R17-R23 Waveform of amplitude 3.5V
lines (following
through to relevant RT side of R1-R8
ICs)
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