Power Supply Unit; Crt Control Circuits; Auxiliary Circuits - Philips PM3055 Service Manual

3-13
* CRT control circuits:
The FOCUS AMPLIFIER
block
is
influenced by both front-panel FOCUS and
INTENS controls
to
provide a
focus that is
independent
of the
intensity, and drives the
focusing grid
G3 of the CRT.
The -100 V BLACK
LEVEL block provides
the
correct presetting
of the
cathode voltage.
The CRT BIAS gives
a
d.c.
voltage to the
grids G4 and G5 to
provide an
optional adjustment for
geometry and astigmatism.
3.2.7
Power supply unit
The mains input voltage is
filtered and
then applied
to
the
RECTIFIER
block
to
obtain a
d.c.
voltage source.
Another output of the LINE
FILTER block
is
routed via the LINE TRIGGER PICK-OFF and serves
as a
MTB LINE trigger signal. The rectified mains source
is
routed to
the
FLYBACK CONVERTER, which generates the
necessary voltages
for the
oscilloscope circuits. Each supply voltage
is
rectified in the
RECTIFIERS block.
The LOW-voltage supplies are stabilized by the CONTROL
circuit
to
the
converter.
The +10 V REF supply serves as a
low-voltage reference
and
is
generated
in
the +10 V
REFERENCE source block. This
reference voltage is
also fed
to the
different circuits on the
power supply
or in the
oscilloscope.
The EHT CONVERTER generates the -14 kV for the
post-accelerator anode
of the
CRT and
the -2
kV
for the
cathode circuits.
*
Auxiliary circuits:
The CALIBRATION
GENERATOR generates the
CAL voltage, which
is
applied
to the
output socket
XI.
The CAL
voltage has
a 1,2
V p-p level with a
frequency of 2kHz square wave.
The ILLUMINATION CIRCUIT determines the amount of current
passed to the
graticule illumination lamp of
the
CRT controlled
by the
ILLUM control
on the
front-panel
.
The
TRACE ROTATION CIRCUIT determines the
strength
and sense of the
current passed
to
the trace
rotation coil around
the
neck
of the CRT.
The current is
influenced by the
front-panel screwdriver operated
TRACE ROT control.