Protection Circuits - Sony KV-13FS100 Product & Training Manual

secondary of the FBT. With the +/- 13V missing, IC545 will not function and IC001 will detect a vertical failure
and place the unit into protection mode.
+135 Supply (OVP and OCP)
Note: Reference Figure 5-2 during the following discussion:
The +135V supply OVP is simply zener diode D614. If +135V line rises above 150V, D614 will break down and
regulate the voltage at 150V. Most likely D614 will be destroyed (shorted circuit) and short the +135V to ground.
Note: D614 is physically connected prior to the OCP circuit (Q590). So, when D614 shorts, all current is sent
through D614. The OCP is not triggered. System Control in IC001 detects a vertical circuit failure due to the
following sequence of events:
Follow the order of events as shown below:
1) +135V is missing
2) +135V is supply voltage to FBT and Horizontal Output transistor
3) No drive to FBT
4) No +/- 13V developed on FBT secondary
5) +/- 13V is supply to IC545 (Vertical drive IC)
6) No Vertical drive output
7) IC001 detects vertical failure
The +135V supply OCP is monitored using Q590, R591 and associated circuitry. The current draw on the
+135V line flows through voltage divider R594 and R595 series resistor R591. If the current rises on the +135V
line, so will the voltage drop across R591. When the current is great enough to cause the voltage drop across
R591 to be approximately 1.2V, Q590 will turn ON. Current will now flow through voltage divider R592 and R593.
Once the voltage drop across R592 reaches 1.2V, D562 and 0.6V will be applied to latching transistor Q572.
The Latch circuit (Q572 and Q573) operates in the following manner: Q572 is forward biased by applying 0.6V
to its base circuit. Q572 then saturates and passes ground to the base circuit of Q573. Q573 turns ON (once the
Latch is activated, it will remain in this state until the unit is unplugged from AC power and reconnected). The
voltage at the base circuits of Q006 and Q608 is reduced below turn-on (0.6V). Q006 shuts off and a High is
applied through R055 to IC001/pin 72 (I-HLDWN). Q608 is simultaneously shut off, which removes the ground
return to the AC relay (RY600). AC power to the Main Switching Power Supply is disconnected and the unit is
placed into Standby Mode. The High at IC001/pin 72 (I-HLDWN) activates the self-diagnostics and the Standby/
Timer LED flashes in groups of TWO.
High Voltage (OVP)
Note: Reference Figure 5-2 during the following discussion:
The HV (OVP) monitoring circuit will also trigger the Latch circuit (Q572 and Q573). The condition of the High
Voltage (HV) is continuously checked by monitoring FBT/pin 7 secondary AC voltage (not shown). This Ac
voltage is fed to a half-wave rectifier circuit D566 and C566. The resulting DC voltage is then applied to IC561/
pin 5. This voltage is proportional the HV and will follow if HV increases. The voltage at IC561/pin 5 is compared
to the reference voltage (10.3Vdc) on IC561/pin 6. The reference voltage 10.3V is developed from +135V using
regulator circuit consisting of D568, D567 and R567. A High will be output on IC561/pin 7 when the voltage on
IC561/pin 5 rises above the reference voltage on IC561/pin 6. This high will activate the Latch circuit as described
in the previous paragraph. Once again, the unit is placed in Standby Mode and the Standby LED Flashes in
groups of TWO.
26

5. Protection Circuits