Sony KDP-51WS550 Training Manual page 21

4. AX-1 Protection Circuits
Reference Figure 4-1
B+ OCP (Q6803) monitors the current draw on the +135V line. If the current should increase due to an excessive
load on the +135V line, the Latch will be triggered and shut OFF the AC-Relay. Also note that there is a direct
connection from the B+ OCP circuit to IC0001 Main Microprocessor for self-diagnostics indication processing.
B+ OVP (IC6801) monitors the +135 voltage level. If an over-voltage condition occurs, the Latch will be triggered
and shut OFF the AC-Relay. Also note that there is a direct connection from the B+ OVP circuit to IC0001 Main
Microprocessor for self-diagnostics indication processing.
IK-Protect 1 (Q8008) monitors the current in the secondary of the FBT using the ABL voltage. If excessive
current flows in the FBT secondary, Q8008 is used to mute the video. Q8008 works simultaneously with Q8007,
which turns off the AC relay.
IK Protect 2 (Q8007) monitors the current in the FBT secondary. If the current increases, Q8007 will disconnect
the AC power via IC0001. Note that this circuit is connected in parallel with B+ OCP circuit and will produce a 2X
flash sequence (same as B+ OCP). Q8007 works simultaneously with Q8008, which mutes the video output.
V-Protect (IC5101) is the vertical deflection output drive IC. The protection circuit monitors the vertical feedback
signal from the VDYs. A feedback pulse is also produced at IC5004/pin 3 when IC5101is working properly and
driving the VDYs. If a vertical failure occurs, the feedback pulse is not produced and the vertical feedback is
grounded. The video is muted (AC-Relay and Audio remain ON).
H-Protect (IC8006) monitors the horizontal deflection output drive. If the horizontal deflection stops, IC8006 will
turn-off the HV converter IC8002 (this circuit is connected in parallel with IC8001 HV OVP).
H-Protect (IC5202) monitors the horizontal pulses. If the horizontal deflection stops, so do the horizontal pulses.
This circuit will cause the Y/C Jungle (IC0401) to blank the video and also shut off the AC-Relay via the PF and
Main microprocessors.
HV LVP (IC8004) monitors the HV output. If the HV is LOW, IC8004 detects this condition and the AC power is
removed via IC0001.
HV OVP (IC8001) monitors the HV level. NOTE: this circuit is on the HOT (or primary) side of the transformer,
so use HOT Ground for measurements. If the HV increases, IC8001 will turn off the HV converter IC8002.
Low B+ Protect (Q0008) monitors the 5V dc level. If the dc level falls below 4.5V, Q2314 detects this error and
the AC input is disconnected.
White Balance Prot. (IC9001, 9002, and 9003) on the CR, CG and CB boards are the cathode drive ICs. Each
IC produces a separate IK pulse directly proportional to the current in each cathode. The current in each cathode
indicates the physical condition of the cathode. Depending on the cathode condition, the set will either increase
RGB drive to the cathode or go into IK Protection mode.
Zero Detect (Q6110, Q6111, and Q6112) are used to monitor the frequency of the AC Input signal at initial unit
power-on. The circuit detects the zero-crossing of the AC signa, and times the power-on of the unit to coincide
with the zero-crossing eliminating as much as possible initial surge currents that could cause damage to the
power supplies. This circuit basically takes the place of the Inrush Relay circuit in previous models.
Audio Protect (Q2005, Q2006, and Q2008) monitors the speaker output for a positive (Q2006) or negative
(Q2005) DC voltage. If a DC voltage exists on either output, the circuit will trigger.
Regulator Protect monitors the various dc regulator outputs for an over voltage condition.
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