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The secondary voltage induced in the S1 - S2 winding is
rectified
by D951
to produce
the +B
(H.T.), which
is
smoothed by C952.
The S3-S4 winding produces +12v via D952, and this is
smoothed by C954.
It is then applied to Q953, and in conjunction with IC951
produces the chassis +9v supply.
Q951 stage controls the H.T. regulation.
The base of Q951 is set to a pre-determined level by the
resistor network R952, VR951, and R951.
Should the H.T. rise, the base current fed to Q951
will
increase, turning the transistor on harder. This causes more
current to flow through the opto-coupler IC901.
An output is then produced from pin 5 of the opto-coupler,
which is applied to the transistor network Q901, Q902.
As these transistors
control the on time of the power
transistor Q903,
a constant
and regulated
H.T. level is
maintained.
ZD952
offers protection to the H.T. circuits should the
voltage level rise excessively.
When the standby mode is selected, pin 20 of I1C001 will go
"Low", removing the drive to Q952.
As a result, Q953
is turned
off, and the +9v to IC201
disappears, therefore shutting down the deflection stages
of the 1C201. E.H.T. generation will then cease for as long
as the standby condition exists.
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