Sony KV-32HS500 Training Manual page 44

4. DA-4 & DA-4X Protection Circuits
HV Protection
(Reference Figure 4-8)
Also attached to the H-Prot. input IC2801/pin 57 is the HV-PROT. This circuit is actually monitoring two functions:
HV OVP and Beam Current through D8043 and D8025 respectively. If an excessive HV or Beam current condition
should occur, IC8006/pin 5 will go High, which will cause IC8006/pin 7 to output a High. The High will forward
bias D8051 and a High will now be applied to IC2801/pin 57 to blank the video. IC2801/pin 52 will then communicate
with IC2300/pin 31 and shut off the AC relay. The standby/timer LED will flash a 7X sequence.
Vertical Deflection Protection Circuit
(Reference Figure 4-8)
IC2801/pin 56 monitors the low side of the vertical deflection coil [V-DY (-)]. IC8003/pin 5 drives the high side of
the V-DY, while the other side goes to ground through R8036. A small vertical feedback signal is developed
across R8036, which is applied to IC2801/pin 56.
If the vertical deflection circuit should fail (no drive to V-DY), IC2801/pin 56 will detect the missing vertical
feedback signal and blank the video output to the CRT. The TV will be placed in Vertical shutdown and the
standby/timer LED will flash a 4X sequence. The AC Power and Audio will remain ON.
IK (White Balance) Protection Circuit
(Reference Figure 4-8)
Each CRT driver IC9101, 9201 and 9301/pin 7 (located on the CR, CG, and CB boards) produces an IK feedback
pulse directly proportional to the current in each cathode (which indicates the condition of the cathode). All three
IK feedback pulses are combined at Q9104 on the CR board and sent back sequentially to IC2801/pin 24.
Each pulse is monitored for level by IC2801/pin 24. If a pulse is low, IC2801/pin 52 will detect a weakened
cathode and IC2801 will increase the drive signal to that weakened cathode until optimal white balance is achieved.
If white balance cannot be achieve within two seconds then IC2801/pin 52 will communicate with IC2300/pin 31
and the TV will go into IK protection mode. The video to the CRT will be blanked and the standby/timer LED
will flash a 5X sequence. The AC power and Audio will remain ON.
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