Sony KDP-51WS550 Training Manual page 15

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10V regulator (IC6501/pin 10)
Note: The 10V output at IC6900/pin 10 passes through D6901 and is then fed back into IC6900/
pin 14, supplying power to the internal driver transistor for the Low & High side output FETS
Q6900 and Q6901.
3) Output Oscillations: At this point, initial square-wave oscillations of approximately 125KHz are output at
IC6900/ pins 16 and 12. Normal operation frequency is approximately 90KHz.
4) Regulator Feedback: The feedback line is connected to the +9V secondary output. Once IC6900 is
turned ON and oscillations begin, the secondary winding at T6900/pins 6 and 8 and associated circuitry
produces +9V. The +9V is applied to IC6901/pin 1 (Control IC).
IC6901 controls the voltage at the PH6900/pin 3, which controls the current output of the optic-coupler
PH6900. The amount of current supplied to IC6900/pin 2 depends on how hard PH66900 is turned ON.
In normal operation, a voltage of 1.8Vdc (which is proportional to the amount of current) is present at
IC6900/pin 2. The feedback loop is now complete.
5) IC6900 Normal Operating Power Supply (VC1): Produced simultaneously with the oscillator feedback
is the operating power source VC1.
IC6900/pin 8 (VC1) is produced using a winding on T6900/pin 5. The AC is rectified and filtered, and a
DC voltage of 15.6V is applied to IC6900/pin 8. Once the 15.6V is stable, IC6900's internal control circuit
disconnects (internally) the power source at IC6900/pin 18. All IC6900 internal circuits are now powered
from IC6900/pin 8.
Also, note the second connection at T6900/pin 5 consisting of components R6925, D6908 and C6918.
This rectifier circuit supplies the Primary Power Supply with its VC1 voltage on IC6400/pin 8 (reference
fig. 3-4)
Over Current Protection (OCP): ref. Figure 3-3
The current flowing through the switching FETS (Q6900 and Q6901) also passes through C6916, T6900/
pins 1 and 3, R6920 and then to ground. The same current also passes through the parallel resistor circuit
of R6908 and R6903. This current is directly proportional to the current through the switching FETS. The
voltage across R66903 is applied to IC6900/pin 9. The OCP is activated when the voltage at IC6900/pin 9
exceeds 0.2V.
Over Voltage Protection (OVP) and Under Voltage Protection (UVP): The voltage at IC6900/pin 8 (VC1) is
monitored by circuitry inside IC6900 for Under-voltage and Over-voltage conditions. The two conditions are
as follows:
OVP – greater than 33V
UVP – less than 8V
If either of these two conditions occurs at IC6900/pin 8, the unit will go into protection mode.
Troubleshooting Tips (ref. Figure 3-3)
NOTE: Follow previously discussed "IC6900 Startup Sequence". The five steps are in sequential order.
NOTE: Use HOT GRND when making measurements on primary side of T6900. This includes all
measurements on IC6900.
Symptom: Unit goes into protection mode, LED flashes in six times pattern.
Check: This indicates either a +5V or +9V shorted condition. Also, there could be a possible open feedback
circuit to IC6900.
1) Check power supply secondary outputs.
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Check 5V and 9V conditions at output of the power supply.
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If the 5V line comes up to proper level and the 9V line goes up to 14V before shut down, a problem
exists in the feedback circuit from the 9V output back to IC6900/pin 2 (open circuit)
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3. AX-1 Chassis Power Supplies