NotTaR of Television Sets : Width and height change with warmup     
 Copyright © 1994-2007, Samuel M. Goldwasser. All Rights Reserved. Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying. I may be contacted via the Sci.Electronics.Repair FAQ (www.repairfaq.org) Email Links Page.

    << Flameproof Resistors |  Index  | Problems with SCR based r.. >>

Width and height change with warmup

Since both width and height are affected, this points to something common like the low voltage power supply. If there are any indications of hum bars, first check the main filter capacitor(s) or substitute a known good one. There might even be other symptoms like faint retrace lines on at least part of the screen.

Start by monitoring the B+ to the flyback (feeding the HOT) to see if this drifts at all. If it does, then there is probably a low voltage regulator problem - bad capacitor, resistor, or chip. Use freeze spray to narrow it down. If this is solid, then there could be a high voltage drift but this would be somewhat unusual without other symptoms (like arcing) since the HV is nearly always tracks the low voltage supply.