Zenith CM-150 Series, Service Manual

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PRODUCT SAFETY SERVICING GUIDELINES FOR AUDIO-VIDEO PRODUCTS
THEORY OF OPERATION (SHUTDOW N CIRCUIT)
The HV shutdown circuit appears on sheet 5 of the
schematics for 9-1979. The basic HV shutdown circuit is
illustrated below.
The peak pulse voltage from deflection transformer
TX3204 is rectified by D3205 and C3217. The resulting
37 volts is then divided by RX3015 and RX3019M to
approximately 8.5 volts. It is applied to the
non-inverting input of one of the op-amps in ICX3200
(pin 10). This op-amp is used as a voltage comparitor.
It’s inverting input (pin 9) is held at a reference voltage
of 9.1 volts by the Zener diode ZDX3004 and RX3025.
Any failure in the deflection circuit that would cause
excessively high, High Voltage at the CRT will also cause
an increase in the sampled 37 volts. This increase will
result in an increase in the voltage at the non-inverting
input to op-amp IC3200 (pin 10). When this increased
voltage exceeds its reference 9.1 volts, the op-amp
output goes from low to high. DX3009 provides a
feedback path that holds the non-inverting input high
so that the op-amp stays
latched with its output high until power is removed by
turning the TV off. DX3009 and RX3016M pull pin 2 of
3N2 high (about 12 volts). This is the horizontal drive
signal pin from the video processor in the small signal
module. The video processor turns off horizontal drive
when its output is pulled high.
When the high voltage shutdown circuit is activated,
IC3200 is no longer supplied with 23 volts to its power
input pin (pin 4) because the 23 volt supply comes from
the deflection transformer, which has been shutdown.
QX3410 and QX3411 provide a connection to another
supply at this time.
The shutdown circuit may be tested for operation by
momentarily connecting a 1k ohm resistor in parallel
with RX3015. This will boost the non-inverting input
above 9.1volts and trigger shutdown.
GM Directview HV & B+
Chassis B+ [VDC] HV (nominal
@ 0 beam kV) HV (max @ 0
beam kV)
135 32.0 33.0
HV SHUTDOW N FOR DIRECT VIEW
GM Direct View CRT Protection Circuit Diagram
3A6
Q3410
QX3408
ICX3405
Q3202
Q3001
Q3002
IC3200
CRX3008
CRX3009
H Drive DR SC
CDisable
(not used GZ/GM)
10 10
9
8
1K
1K
2K
9.76K 110K
5.6K
1uF
100uF
CRX3010
CRX3012
CR3012
1K
Q3000
CR3016
CR3003
1K
10K
CR3004
15VSW
50VPSW
CR3405
10K
470
4
3
2
1
1K
15VSW
15VSB
15V Ref
to ICX3401-15
To ICX3401-14
SW On
1K
PW R CTRL
12VSW
1
8
CR3005
CR3006
8.56K
10K
0.47uF
8.56K
10K
PwrCntrl
15VSW
15VSW
1K
Blank
CR3014
CR3212
CR3210
1K 1K
130K
1K
2.2M
56K
1.8K
15VSB
250V
4.7uF
+ -
G1SK
4.7uF
+
-
15K
G1
1K
330K
390K
740V
10K
10K
51K
CR3002
CR3001
10uF
100
+
10uF
+
10K
1M
VSense
3B5
1
8
250V
15VSW
Blank
G1
Gnd
6.3VAC Fil
Fil. Gnd
nc
To Video Output
Modules
From Small Signal
Module
Daughter Module
A - 17821 - XX
ABL SW 9.1V
Ref
0V = normal
12V = fail
30V
-5V
with
scan
2V
with
scan
L = normal
H = fail
L = normal
H = shut down
-250V
20V
normal
shut down