Assignment 7

PROBLEMS AND SOLUTIONS OF TV HORIZONTAL SECTION

Introduction
This is the section in the receiver which receives the high voltages. It is responsible for the deflection of the beam in the horizontal direction. It receives the high voltages form the flyback. The main problems may lie on the high switching diodes or the capacitors. Some of the problems would include:

• No Raster, No sound

This is usually caused by a failure in the high voltage supply, accounted by the loss of raster and sound. This points to the horizontal output transistor, which is inoperative. What could have caused the shorting of the transistor could be shorted turns in the yoke, a shorted flyback transformer, a shorted high voltage rectifier, a shorted pincushion transformer, an open tuning capacitor, a shorted scan rectifier, incorrect horizontal drive frequency and high voltage arcing. One should never eliminate one and not test other devices. In this section of the receiver, it’s imperative to be sure.

• Insufficient or Excessive Width, All Else is Functional

This can be caused by a reduced power supply voltage, a leaky capacitor other leaky or shorted components. It can also be caused by a tuning capacitor that is too small or too large.

• The Horizontal output transistor (HOT) keeps blowing

This may be caused by dried up capacitors, open resistors or chokes, bad connections, or a driver transformer with shorted windings or broken or loose core. Excessive voltage on the HOT collector (check LV regulator) can cause this problem or defective safety capacitors or damper diode around the HOT. A new transistor not mounted properly to a heat sink may cause this and probably needs a mica washer and heat sink compound. Another possible cause for random failures of the HOT are bad solder connections in the vicinity of the flyback and the HOT as well as the horizontal driver and even possibly the sync and horizontal oscillator circuits, power supply, or elsewhere

• Lose of horizontal sync

The problem lies either in the horizontal oscillator or in the sync system. If it really is a problem with sync pulses not reaching the oscillator, the picture will move around horizontally and can be brought to hold momentarily with the hold control. If the picture breaks up into strips, there is a problem in the horizontal oscillator. One should rotate the hold control: if the frequency is too far off, the picture will not settle into place at any adjustment of the hold control. One should look around the horizontal oscillator circuit: all of the oscillator parts will be right there, or check on the horizontal oscillator module.
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