Sony KV-32HS500 Training Manual page 46

As the current in the FBT secondary increases, the ABL line will pull increasingly more current through the
voltage divider network at the top of R8190 and less current will flow through R8190. The voltage drop across
R8190 will decrease, causing the combined voltage drop across R8191 and R8190 to decrease. At the same
time, the 0.6V at the base of Q8029 is decreasing, which turns OFF Q8029. A High will now be developed at the
collector through pull-up resistor R8173. D8023 is now forward biased and a High is applied to IC8007/pin 5. A
High will now be output at IC8007/pin 7 and Q8022 will turn ON and stop H drive at the emitter of Q8041,
stopping the HV.
IC8006/pin 5 has the identical function as that of IC8007/pin 5 just described. These are backup FBT OCP
protection circuits protecting against excessive beam current in the CRT. IC8006 uses Q8021 switch to stop H
drive at the emitter of Q8041.
IC8006/pin 3 protects against excessive HV the same as IC8007/pin 3. The difference between the two circuits
is where the HV is monitored. IC8007/pin 3 monitors HV at the HV Block whereas IC8006/pin 3 monitors the HV
using a coil in the primary side of the FBT located at FBT/pins 5 and 6. The output at FBT/pin 6 is directly
proportional to the HV. If HV increases, so will FBT/pin 6. The output is rectified, filtered and applied to IC8006/
pin 3. The function after a High is applied to IC8006/pin 3 is identical to IC8007/pin 3 described above except
Q8021 is used to stop the H drive at the emitter of Q8041.
The Standby/Timer LED flashes a 7X sequence when a failure occurs.
Regulated 5V Protection Circuit
(Reference Figure 4-10)
The regulated 5V line is monitored using Q2314 and Zener diode D2310 (3.6V) on the M-board. The output of
the 5V regulator IC504 is applied to the emitter of Q2314. In normal operation, Q2314 is turned ON and D2310
is conducting holding the base at 3.6V. Approximately 2.8V is applied to System Control IC2300/pin 43 indicating
proper level of the regulated 5V line.
If the 5V line falls below approximately 4.5V at the emitter of Q2314, D2310 will stop conducting, Q2314 will turn
OFF and a Low will be applied to IC2300/pin 43. IC2300/pin 69 will then turn OFF the AC relay.
The AC relay shuts down and the Stby/Timer LED flashes a 6X sequence.
R2298
R2300
D2310
3.6V
O
IC504
G
5V REG.
I
A BOARD
UNREG. 7V
FIGURE 4-10 - REGULATED 5V PROTECTION CIRCUIT
SYSCON
IC2300
(I-LB-ERR)
43
R2375
Q2314
R2299
C2361
44
4. DA-4 & DA-4X Protection Circuits
M BOARD
C31P15-4-10 11/12/02