Sony KDP-57XBR2 Training Manual page 104

High Voltage Shutdown: Verification of an over-voltage or over-current condition must be checked first. Monitor
the AC current draw at shutdown to determine which is causing the condition.
Excessive Current: If the AC current exceeds 2A or more immediately at turn-on, begin by disconnecting
the HV block from the circuit. The circuit will still shut down since the error loop for the PWM has been
removed, but the current level will drop significantly if the block is defective. If the current remains
excessive, check for shorts on the filament or 200V line. T8004 or T8005 could be defective and can be
tested by following the procedures in the previous section on replacing a shorted Q8038.
Nominal Current: Either the high voltage level has exceeded acceptable limits or the protect circuits are
activating erroneously. Verify Q8035 is not shorted. The HV block has an extra output port for testing the
HV level. Simply remove the cap and insert a HV probe. This is a very important step. If the high voltage
level is excessive, extra caution must be taken while diagnosing the circuit. Due to the small size of a
projection CRT, it is easy for the high voltage to exit the anode cap and arc to the deflection yoke. This
usually cracks the CRT. Turn the set on and watch the HV meter for a reading before the unit shuts down.
Normal HV should read 31± .40KV. A properly functioning and adjusted protect circuit will trip at 34.5±
.50KV so you should be able to see this with the probe.
High Voltage Exceeds 35KV: Connect a DVM with peak-hold to pin 12 of IC8008. The voltage should
read approximately 7.5VDC. A peak voltage of 7.5V or less indicates a defective HV block or IC8008 is
loading the feedback line. If the voltage level exceeds 7.5V by a considerable amount, the feedback loop
from the HV block is OK and the PWM generator is not operating properly or the tuning components at
Q8034 are defective.
To isolate the problem, take a peak reading at the output (drain) of Q8035. If the PWM circuit is operating
properly, the voltage should be substantially less than the 135V supply. This indicates the PWM circuit is
attempting to reduce the HV level. Suspect an open C8123 or C8124 (not shown) at Q8034-C. Full
voltage at the input and output of Q8035 indicates a short or leakage of this component or an improperly
operating PWM circuit. Check VR8001 for resistance at the contact wiper to both ends along with a
reading from end to end. If this VR fails, the high voltage will rise to maximum potential.
High Voltage Reads Approximately 31.5KV: The regulator stage is assumed to be working correctly. The
protect components are inappropriately firing. If the unit is going into full shutdown, troubleshoot IC8006
and its associated components. If the unit is only shutting down the HV circuit, check IC8007 and its
components. As illustrated in Figure 25-2, both IC8006 and IC8007 use a 5.1VDC reference at pins 2
and 6. Pin 3 of IC8006 monitors a voltage sample of T8005. Pin 3 of IC8007 monitors a HV block sample
from PWM IC8008. FBT ABL is monitored by Q8028 and Q8029. These transistors are normally on
unless FB current becomes excessive and the ABL voltage approaches zero volts.
Check for proper reference level if 5.1V at the inverting inputs of both ICs. If OK, check for voltages at the
non-inverting inputs that exceed 5.1V. If none exceed 5.1V and pin 7 of either IC is high, replace the IC.
25. RA-6 High Voltage Circuit Troubleshooting
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