Sony KDP-57XBR2 Training Manual page 74

business. This supply has ± supply rails, so do not forget to read across them for low resistance readings.
A quick visual check for overheated components is also a good idea. Check for open fuse links on the
secondary lines, as these are valuable clues. If the above items check OK, the supply can now be
started.
Primary Supply Starts - Unit Shuts Down: Two rapid relay clicks are heard followed by a third click one to several
seconds later. The big question is whether the problem is in the primary supply. The unit is shutting down and
many other areas can be the cause. A good way to approach this situation is to monitor AC current draw.
Low AC Current Draw: If it is low at power up, check the 6.5V source generated by the primary supply
during initial turn on. Troubleshoot the regulation stage if it is too high. If it is significantly low, the
regulation circuit may be at fault or the oscillator is staying in startup mode due to loss of VC1 at pin 8 of
IC6002. This line is protected by fusible resistor R6082.
High AC Current Draw: In order to isolate this condition to the primary supply, disable the secondary
supply by grounding pin 1 of IC6001. Although the unit will still shut down, the loss of high AC current will
eliminate the primary supply as the source. If high current draw remains, the failure is isolated to the
primary. Chapter 17 will deal with shutdown problems.
Regulation Problems: Since the diagnostics circuits monitor the 6.5V source for OVP, problems in this circuit can
be isolated quickly. Verify a legitimate problem by measuring the 6.5V at turn on. If it stays at 6.5V, suspect a
faulty zener diode D6133 or Q6110, Q6111 and associated components. If the over-voltage condition is occurring,
locating the component is done by grounding pin 2 of IC6002. This should bring the 6.5V line below its normal
voltage by forcing the oscillator to a higher frequency. If not, IC6002 is faulty. If the 6.5V source drops, work your
way back by grounding pin 1 of PH6005 followed by pin 3 of IC6107. Grounding any one of these lines should
bring the 6.5V below normal level. If grounding these points does not reduce the voltage, the problem is likely
one of the sampling resistors (R6162 or R6163). Error amps such as IC6107 are very reliable and should be
suspected least.
Secondary Power Supply
The operation of the secondary supply is virtually identical to that of the primary, as shown in Figure 16-3. It
generates the higher voltages in the set and drives two transformers instead of one. The sources needed to turn
it on are different from the primary. It requires unregulated B+ like the primary but the startup line at pin 18 of
IC6001 is not used. The V sense line is still used to monitor unregulated input. It is also used to control the
oscillator on via a high from the VCC line. A main SW high from IC001on the B board controls this line. It is also
controlled by latch transistors Q6004 and Q6005 for protection. VC1 at pin 8 is supplied by the primary supply to
provide the oscillator with its operating voltage. This is why the secondary supply cannot operate without the
primary running.
Regulation is controlled by monitoring the 135V line instead of 6.5V. Two transformers are driven T6001 PIT and
T6002 PIT AUX.
16. RA-5A Power Supply Troubleshooting
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