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NotTaR of Television Sets : Trailing lines in one or more colors
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.
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Assuming this is not a form of ghosting resulting from poor reception
conditions, then it could be any of the following:
- Poor decoupling in the power supplies for the video drive circuits - probably
on the CRT neck board. Check for bad (low uF or high ESR) filter capacitors
(electrolytic mostly) on this board or the power supplies feeding it.
- Insufficient CRT filament voltage. This could be a result of bad connections
or a bad component in the filament power supply (probably from the flyback).
Check to see if the filaments are glowing bright orange and check the voltage
if possible (though this can be tricky since it is often fed from a winding
on the flyback and is a pulse waveform, not DC or a sinusoid. The service
manual (or Sams' Photofact) will probably have info and waveforms.
- Bad CRT (more likely if only one color is affected). A weak electron gun can
result in this behavior. Swap it with one that work properly. If the same
color is still bad, that CRT gun is weak. The CRT will need rejuvenation or
need to be replaced (more likely, the entire TV will be tossed into the
dumpster).
One simple test would be to swap two of the color outputs to the CRT
pins. If the behavior moves with the swap (i.e., from red to blue), then it
is likely an electronic problem. If it is still the same colors, it is
probably the CRT.