Assignment 9

TV Sound Section Problems and Solutions

Introduction

Problems that occur in a television’s sound section are usually not accompanied by any picture problems. This report will discuss the common problems that are encountered in every day use of a TV

Symptoms and Possible solutions
Problems caused by external blocks

If there’s poor sound quality accompanied by an unstable picture, the problem may lie in the AGC circuits. If the sound and the picture do not track properly, this may be a problem with the detector coil or a poor sound alignment. A hum or a running sync suggests a problem with the sync section or the AGC circuits.
Squealing or whistling, distorted or intermittent sound or no sound accompanied by a normal picture and raster will lead us to the following procedure in the sound section

Sound Section
Inject a signal into the speaker to make sure that the speaker is operational. If a hum or a tone is audible, then the speaker is not faulty. But it is still wise to check the speaker for beaks or warps in the cone. Check the speaker impedance and relate it to the indicated value.
If the speakers still do not produce sound, then there could be an open connection in or around the audio amplifier, however, trace the sound from the video section, through the sound IF, the sound detector or the amplifier to eliminate other possible causes.
If the sound for the speaker is continuously humming, then the audio amplifier is the most probable cause for this fault. A humming sound could be caused by a leaky or open transistor or capacitor, a change in resistance or voltage that could be too high or too low, Check the output of all stages and match the theoretical values to the actual ones, its best to trace back form the speaker, this may help in isolating the fault more quicker. If the sound is weak and slightly distorted, then adjust the detector coils to remove the frequency variations. If the television is using an IC, then test all pins for the expected voltages. Squealing or whistling sound may be a faulty transistor or capacitor in one of the audio stages. Check each component around the IC and compare the measurements with theoretical values.
If there’s a popping or cracking sound, check the audio amplifier stages and test the transistors. One may have to remove them from the circuit; open filter capacitors can also cause this fault. If the sound is mushy (blatting) when the volume is turned down or dull, low pitched and vibrating when turned up, there could be a faulty transistor, resistor, or poor sound alignment.
Loose wiring and open or shorted connections cans also cause intermittent sound problems. With the chassis and speaker on, lightly pull all the components to ensure that they are connected, use a cold spray to detect cold solder or heat sensitive components.

Reference:
Howard W. Sams, Troubleshooting and Repair Guide to TV, 1st Edition, ©1996 by Howard W. Sams and Company, Prompt Publications, Indianapolis, Indiana. Pg 116-120