Philips 7592, Руководство по обслуживанию

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Troubleshooting Tips
Troubleshooting tips for the deflection and power supply circuitry.
The Deflection Circuit:
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Measure for VBAT (140V) across 2939/2940 (Section - A1 POWER SUPPLY). If the voltage is not present, disconnect
jumper 9936 and 9937
(see A1 Power Supply) The complete Line Deflection stage is now disconnected. If the voltage is
present then the deflection circuit may be the cause of the problem.
Possibilities include:
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Defective Transistor 7410
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Faulty driver circuit around transistor 7481
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No horizontal drive signal coming from the BOCMA (signal processor) IC 7301 pin 56 on the SSB
Note: If the Collector and Emitter of 7410 are shorted, a “hiccup” noise may be heard from the power supply circuit.
To determine whether the fault is present in the line deflection circuit (Section - A2 LINE DEFLECTION) or in the EW
circuit/panel (screen size above 21”), insert jumper into position numbers 9409 (in this case the EW protection is disabled). If
the basic deflection is working (picture is parabolic distorted), then the fault is located in the EW circuit/panel. If there is no
horizontal deflection, the fault is present in the basic deflection circuitry.
Also take note of protection circuits in the line output stage. If any of these circuits are activated, the set will shut down.
Depending upon protections, the LED will blink according to the fault defined. In order to determine which protection circuit is
active, isolation of circuits is necessary. These protection circuits are:
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High beam protection. See error 1 - High Beam Protection.
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X-ray protection : See error 1
If the high beam protection or the X-ray protection is active, it will switch the set to protection and the SDM will be automatically
activated. The service LED blinks repeatedly 1 time. If this happens, isolate each circuit to determine the cause
The Power Supply Circuit:
Trouble-shooting the H8 Switch Mode Power Supply (SMPS)
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First check the +5V_STBY voltage on IC 7968, pin 3/4.
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If this voltage is not present, check fuse 1961 and D6961.
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If there is not an open circuit at 1906 or D6917, the problem may be caused on the primary side of the switching supply.
Check the output of the bridge diodes on the cathode side of D6912/D6913 or D6915 - pin 1 for approximately 150V DC.
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If this voltage is not present, check the bridge diodes and the fuse.
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If fuse F1900 is open, check IC7921 (circuit A1) between pins 2 and 3 to insure that there is no short circuit present.
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If the 150V DC is present on pin 3 of IC7902, check for a startup voltage of 16V on pin 4 of IC7921.
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If the startup voltage is not present, check R3914 for an open circuit; a short circuit between pins 4 and 5 may also be the
cause of this problem.
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It is necessary to have a feedback signal from the hot secondary side of switch mode transformer T5912 at pin 8 and pin 9
for the power supply to oscillate.
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If this startup voltage is present on pin 4 of IC7902 and the supply is not oscillating, check R3929 and D6929.
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The H8 power supply has been designed with Over Voltage Protection (OVP).
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To determine whether OVP is active, check whether VBAT – 141V is present at IC7971 pin 1. If not, check the components
D6938, C2939 and C2940 and L5941.
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If these components are O.K., then check voltage at pin 3 of IC 7942.
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If this voltage is not present check fuse 1941 and fuse 1942. Replace if necessary.
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If dc-voltage is present at pin 3, replace opto-coupler 7929.
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Another way to confirm whether OVP is active is to measure the voltage with an oscilloscope at IC7902 pin 4. If the voltage
is fluctuating between 11-14V, then check the components described above.