Q-Box, Primary And High Voltage Power Supplies - Sony KDP-51WS550 Training Manual

TV will have problems turning ON. If C6120 became defective (open circuit), the AC voltage input can only go as
low as 105VAC before erratic TV turn-ON function.
At the same time the AC Relay is energizing, Q6109 is turning ON. When Q6109 turns ON, it shorts the emitter
to base on Q6107 and it turns OFF. Once Q6107 turns OFF, D6120 reverse biases, D6123 forward biases and
applies a HOLD voltage of 7V from the standby power supply to the AC Relay to hold the relay ON in the ON-
Mode.

Q-Box, Primary and High Voltage Power Supplies

Reference Figures 3-3, 3-4, 3-5
All three power supplies use the same converter IC (MCZ3001D) as the heart of their separate switch-mode
power supplies, along with two drive MOSFETS and associated components. MCZ3001D contains all the circuitry
necessary to function as a switching power supply (except for the Power Switching MOSFETS). It contains:
Control Circuitry
Oscillator/Oscillator Control
Output Driver Transistors
10V Regulator
Soft-Start / Delay Shut-Off Timer
Over Current Protection
Over and Under Voltage Protection
The same basic circuit Theory of Operation and Troubleshooting Procedures described in the imminent paragraphs
can be applied to all three Power Supply circuits.
NOTE: The Q-Box Power Supply component reference numbers will be used in the following circuit description
and troubleshooting procedures, just change the component reference numbers to apply the descriptions and
procedures to the Primary and HV Power Supplies. There are a few circuit connections that are different between
the power supplies, which will be addressed in the text under the appropriate diagram. The only other difference
between the power supplies is the operating frequency and some slight voltage readings, which are illustrated on
each separate diagram.
Switching Power Supply Operation
Reference Figure 3-3 for the following circuit description.
AC signal is applied to the rectifier block D6005. The AC component is filtered-out by the filter circuit (circuit not
shown; located on A-Board). A DC voltage of 296V is produced at the output of the filter circuit.
IC6900 Startup Sequence
1) Turn ON Voltage: The 296Vdc from the filter circuit first passes through fusible link resistor R6918 and
then is voltage divided by R6907, R6904, R6900 and R66902 down to 2.5Vdc. This voltage is applied to
IC6900/pin 1 (Vsense) and IC6900 turns ON. IC6900/pin1 (Vsense) is also used for OVP protection
(IC6900/pin 1 > 8V will trigger OVP).
2) Internal Circuit Start Voltage: The 296Vdc also passes through voltage dropping resistor R6909, and
279Vdc is applied to IC6900/pin 18. This voltage is used to initially power the internal circuits and begin
oscillations. Note that the 296Vdc from R6918 is connected directly to the Drain of Q6900 and serves as
the High-side FET power source.
Internal circuits initially powered by IC6501/pin 18
•
Internal drive transistors for the output FETS Q6900 and Q6905
•
Oscillator
•
Control circuit
12
3. AX-1 Chassis Power Supplies