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2-13 Protection circuit (RC transformerless
model)
This chassis employs two kinds of protection
circuit, one controlled
by software through the
CPU and the other by hardware.
Protection circuit (software)
The protection
circuit is provided to disable the operation of the TV set in case of a circuit
malfunction.
When an abnormality
occurs during
TV reception
it causes
pin 31 of the CPU to go
continually
Low (less than 0.8V) for about one second.
The CPU detects that this has
occurred and outputs the signal to cut off Q551 and Q554.
Protection circuit (hardware)
When a power failure is detected
by diodes D565, D566 and D564, this protection circuit
operates causing the power oscillation to stop.
If one of the above diodes is turned on, the voltage of Q553-emitter
decreases,
and it turns
on completely.
Photo-coupler
D515 is driven by this and generates
a current which drives
-
Q512 on. As a result, the operation of the power oscillation circuit is stopped.
Under normal circumstances
these parts, D515, Q553, D561, R552, R553, VR551, are
operating as the error detection and regulation circuit for B1 +130V power supply.
-=—.—=—
1.,.,
. . . . . . . . . . . . . . . . . . . . .
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0551
!
Vert.&Horiz
:.. .. ........
:
: :
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:
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T511
j
.—. —.—
.—
:...-......:
:
. .
:
Power
~
.—. —.—.
—
supply
j
circuit
~
.—. —.—
.—.
;
;
: :
:
: :
.........."........"M .."
CPU
Protect 31
Power 4S
Normal
Power faiiuer
operation
I
T
v
R780
lOOk
I
~
Power On
~.aoo,...........,
............................... ~
Stand-By
,
circuit
;
:
;
~
DS93
:
. ..... ............
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—
D515 :
:
~
:
~
~
R552
VR551
:
R553
~
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IlalaI*
Regulator
circuit
Norma
operation
-
-20-
A7-A
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