SONY TRINITRON KV-1404 [NO SOUND: PICTURE OK]
Before proceed to repair, note whether the sound mute function is On. If ON, make it OFF. If this setting is alright, check the voice coil of the speaker with a multimeter. If speaker also has found good then proceed.
- Check all the solder terminals [9 of them] of the audio output IC (IC251_ TDA 2007). It is best to resolder all these solder terminals of thie IC, by applying a little more solder, becuse some loose solder points are very difficult to detect, as they might be microscopic to normal vision.
- If all of above are found OK, check the supply voltage comes to this IC. Its main supply voltage is given to its pin (8). 14VDC should be present at this pin. This voltages comes from SMPS power supply section, through a resistor [protection resistor]. [R613 - One Ohm]. Check this resistor for continuity. If found open, make sure that there is some short circuit with the circuit related to audio output section.
- Check (C251 - 1000Mfd 25V) for short. It is best to measure the voltage between pin number (8) of the audio output IC to main ground. In most cases, if the measure resistance is very low; say lower than 15Ohms or so, the audio output IC is likely to be shorted. Resolder out the audio ouput IC from circuit, and measure this resistance. Still found low, repalce [C251-100MFD 25V). It is shorted.
- If the voltage at pin (8) of audio output is found OK, and thee is no output from the speaker, check the voltage at pin (9) [audio output]. It should be about 6.8VDC. If this voltage is found abnormal [approximately equal to the supply voltage - 14VDC of found to be zero volt]; Without any doubt, repalce the audio output IC. It has damaged.
In this set, sound processing section is inside the video IF unt [IF201 - IFB 389HS]. Check the voltage at teminal (8) of this unit, (audio out). This voltage should be about [3.6VDC]. This is the audio signal output pin. Electronic volume control is used here. The intensity of audio signal appear at pin (8) will depend upon the applied voltage at terminal (70 of this unit. Check the voltage at this point. It should vary, as we increse the volume of the set, either by its front panel of remote volume control buttons.
This voltage comes from pin number (2) of main system control IC [IC 002 - PCA 84C640P-016]. Being picture is OK, sound must be there, as video IF signal out from the video output will have audio signal with it. Because, audio signal is being modulated with video IF signals. The main function of audio processing section is to seperate and to pr-amplify these signals to sufficiant level to drive the audio output IC.
The voltage at pin number [2] of the system control IC, stated above should vary according to the level of volume we set with panel controls. So if there is no voltage deveation present at termianl (7) of video IF unit, come to this check point at pin number (2) of main system control IC. If voltage varies here with adjusting the controls, and not appear this difference at terminal (7) of VIF module, check [R093 -2K2, R030-3K3, R091 - 1K, C017 - 10MFD 63V and R011 - 100K, Zener diode D200 - 6.2V Zener diode, R 211 - 10K]. Check the Zener diode D200 for short]. Check the assicated components connected to termianl (7), if any.
If all are Ok, and still there is no votage variation at pin (2) of main system control IC, it is defective, and should be repalced. If there is voltage variation at pin (20 of system control and terminal (7) of VIF module, and still there is no sound output, make sure that the video processing section inside the VIF unit is faulty. There is no repair to this unit. It should be replaced with same number.