Assignment 8

The sync seperator

Introduction
The sync seperator is very important in the tv because it syncronises the vertical section and the horizontal section.This report descuses the problems and solusions of the sync seperator.

• Loss of Vertical Synchronization or Rolling

After other obvious causes have been eliminated, this problem can be caused by a defective tube, an open integrator transistor, a shorted integrator capacitor or an open resistor between the sync separator and the vertical oscillator. If there’s a hum accompanied with the symptom, it can be caused by poor B supply filtering. The best way to approach this is to test all components and check all outputs for expected readings in order to isolate the problematic component.

• Loss of Horizontal Sync

If this symptom is not accompanied by a loss of vertical sync, it may be assumed that the sync stage is working and the problem lies in the horizontal section, otherwise it may be caused by a defective horizontal sync amplifier, and an open or leaky capacitor in the horizontal Automatic Frequency Control (AFC). A defective AFC may also cause this problem. Test all components in the horizontal sync to isolate the cause.

• Loss of Vertical and Horizontal Sync

This problem indicated that the deflection oscillators are free running and that either the video is not reaching the sync separator or the sync separator is not functioning. One should trace the signal to determine where it halts or diminishes in order to find the cause. The possible components that could be defective are a transistor in the sync or noise limiter stages, open, shorted or leaky video coupling capacitors or a change in value of the video sync isolation resistors (possibly open).

• Horizontal Bending or Pulling

This may be caused by a defect in the video strip, the AGC section, the sync separator, the horizontal AFC or the low voltage power supply. An overloaded video strip may be the cause of this symptom due to a bad hum modulation in the low voltage power supply section. One should check all the filter capacitors in this section to locate the fault. Other causes may be a defective transistor or IC or a leaky coupling capacitor. Due to the vast possibilities in this problem, one should test all components and work up the sections to the sync separator strip to best isolate the problem.

• Vertical Jitter

The picture in this problem seems to lose vertical synchronization and may be the result of poor waveform separation, such that the picture appears to bounce. This may be caused by a defective IC or transistors in the sync separator section, or a defective component in the integrator section. One should trace the signal form the video section and isolate the section which withholds the output, then isolate the defective component by testing each one.

• Lack of sync horizontal

The picture drifts smoothly horizontally. Depending on the difference between the video horizontal rate and the free-run frequency of the horizontal oscillator, the picture may be torn left or right is a special case where the frequencies are virtually the same. This may mean that the horizontal sync signal is missing due to a sync separator problem or that there is some a fault in the sync processing circuitry. Trace forward and isolate the cause.

• Incorrect lock horizontal

This may mean a more-or-less stable torn picture. This means that the sync signal is reaching the deflection system but that it is having problem locking to it. The horizontal oscillator free-run frequency may be too far from what it is supposed to be.

• Lack of sync vertical

The picture rolls smoothly vertically. This may mean that the vertical sync signal is missing or the deflection system is ignoring it.

Conclusion

Sync Problems usually reflect on the picture tune as irregularities in the raster but not sound (usually). One can visually determine its malfunction externally and save a lot of troubleshooting time.

Reference:

• Samuel M. Goldwasser, Notes on the Troubleshooting and Repair of Television Sets, Copyright © 1994-2007 Samuel M. Goldwasser, http://www.repairfaq.org

• Alvin A. Liff, J.A. Sam Wilson, Color and Black and White Television, Theory and Servicing, 3^rd Edition©1993 Prentice Hall Inc. upper Saddle River, NJ 07458