High Voltage Protection Circuit - Tatung OMNISCAN SERIES Service Manual

3.25 HIGH VOLTAGE PROTECTION CIRCUIT
(Refer to circuit diagram Fig-25)
The high voltage protection circuit triggers when the
voltage is grossly over voltage and liable to cause
harmful X-ray emissions from the CRT. The winding
on T603 (pin 6) produces a flyback pulse train of
amplitude proportional to the final anode Voltage.
This is DC-restored by D617-C631. Potential divider
R634-R641 and R640 determines the protection
voltage, in the normal operation region, 0618-0619 is
off. About the upper limit, the DC-restored voltage is
sufficient to cause zener diode 0618 to conduct, pin
13 of Q403 is triggered, Q403 is held off.
Pin 13 is also controlled by horizontal deflection
output pin 4 of T401 via 0413-0414. Potential divider
R487-R488 determines the protection voltage.
HIGH VOLTAGE PROTECTION CIRCUIT Fig-25
~. DF.f PR01 F.CT I ON
3.26 SYNC. SIGNAL (HOR. AND VERT. SYNC.)
PROCESSOR
The product is designed to compatible with worksta-
tion, computer or adapter card having the different
sync. signal such as G+SYNC., COMPOSITE SYNC.
or SEPARATE SYNC. signals.
G+SYNC. - - - - > ~~~~Ff:ig~o ----1-------> ~5~;KT. ------------------>101
Q052, Q053
I
r
-----> SYNC. SW.
Q551
I
I
I I
HjH+V
SYNC. MODE
I
r---> POLARITY
DETECTION
I I
DETECTION
0507, C552
I I I
I I I I
I I I
~--'----------~--------->
H POLARITY
I I I
I I I
Q562b
I I I I
I
L-----r----->
~--------------------->
CLAMP PULSE
I I I
H + V BUFFER
------~
" H SYNC.
H -> Q562a
V
BUFFER
Q553
t - - - - - - - - - - - - - - > H SYNC.
I
t----> Q515a ----------> H SYNC.
I
(MICRO)
I
V SYNC.
> SEPARATOR - - - > 102 ----> 102
=
3-24
=
Q553, Q552 CKT.
Q562c Q515b
I
I
V POLARITY - - - - - - - - - - > V POLARITY
DETECTION - - - - - - - - - > V SYNC.
Q556, Q559
Q562d