Philips 43P 8341 Service Manual Download

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Troubleshooting Tips

The Power Supply Circuit

When the set is turned On, the Main Switch Mode power supply is turned On. This supply produces the
+130 volt,+32 volt,-32 volt, two +15 volt, and Audio supplies. When IC 7302 develops a normal steady
state operation, the 130 volt supply is sampled by resistors 3324,3323,and 3322.

This sample voltage is then sent to Shunt regulator 7303 which drives the feedback optoisolator 7303.The
feedback voltage on Pin 14 is then compared with an internal 2.5 volt reference by comparator "C".
Comparator "C" then sets the reference voltage on the inverting side of comparator "B" to control the On
time of the drive at Pin 3.If the voltage on Pin 14 increases due to the 130 volt supply increasing, the On
time of the pulse on Pin 3 will be reduced. If the 130 volt supply decreases, the voltage on Pin 14 would
decrease, causing the On time of the pulse on Pin 3 to increase. This is used to keep the 130 volt supply
at the correct voltage. Variable resistor 3322 is used to adjust the 130 volt supply to the correct level.

The overvoltage protection circuit of the IC will shut the IC down if the VCC level on Pin 1 exceeds 17 volts.

To troubleshoot this circuit, first check the On/Off line from the Small Signal Panel to ensure that it is
going Low. Then check for the presence of startup voltage on Pin 1 of the regulator IC 7302.If the IC is
working correctly, this voltage will be changing from 9.4 to 14.5 volts. If the startup voltage is not present,
check the startup resistor 3300 and the bridge rectifier. If the voltage on Pin 1 is changing, check the drive
signal on Pin3.Then check for signal on the gate and drain of 7301.An excessive load on the secondary,
a short on the 130 volt line for example, would cause the supply to pulse with little or no voltage on the
secondary.

Picture problems

Picture too dark or too bright

Press “Smart Picture” button on the remote control. If this improves the picture, increase / decrease
the brightness value or increase / decrease the contrast value.

Enter the Customer Service Mode. If this improves the picture, exit Customer Service Mode, then
Increase / decrease the brightness value or increase / decrease the contrast value.

White line around picture elements and text

Press “Smart Picture” button on the remote control. If this improves the picture, decrease the
sharpness value.

Enter the Customer Service Mode. If this improves the picture. Decrease the sharpness value.

Snowy picture

Snow is an antenna or antenna connector problem. Check tuner and AGC.

Black and white picture

Press the “Smart Picture” button on the remote control. If this improves the picture, increase the color
value.

Enter the Customer Service Mode. If this improves the picture. Increase the color value.

Menu text not sharp enough

Press the “Smart Picture” button on the remote control. If this improves the picture, decrease the
contrast value.

Enter the Customer Service Mode. If this improves the picture. Decrease the contrast value.

Sound problems

No sound or sound too loud (after channel change / switching on)
- Enter the Customer Service Mode. If the volume is OK, increase / decrease the volume level.