Since the tuner and sound are ok, horizontal deflection which usually
generates power for most of the set is also working.
|NotTaR of Television Sets : Blank picture, good channel tuning and s..
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.
<< Charlie's comments on foc.. |
| Purple blob - or worse >>
Does 'blank picture' means a totally black screen with the brightness and
contrast controls having no effect whatsoever? Or, is there is no picture
but there is a raster - scan lines on the screen? The direction in which
troubleshooting should proceed differ significantly depending the answer.
Here are some questions:
- As above, is there any light on the screen at any settings of the brightness
and contrast controls, and/or when switching channels? Can you see any
raster scanning lines?
- Can you hear the high pitched (15735 Hz) of the horizontal deflection?
- Looking in the back of the set, can you see the glow of the CRT filament?
- Do you get that static on the front of the tube that would indicate that
there is high voltage? Any cracking or other normal or abnormal sounds
Possible causes of no raster:
- No or low high voltage (low voltage, deflection, or high voltage power
- Fault with other voltages like G1 or screen (G2) to CRT.
- Filament to CRT not getting powered.
- Drive to CRT bad/shut off as a result of fault elsewhere. For example,
failure of the vertical deflection may disable HV or blank the screem to
protect the CRT from burn-in due to the very bright horizontal line that
would result. With some sets, it is possible that the X-ray protection
circuitry will blank the screen without affecting tuning or audio.
Possible causes of no video (but a good raster): Problem in video IF, video
amplifiers, video output, cutoff due to other fault.
It could be as simple as a bad connection - try gently prodding the boards
with an insulated stick while watching the screen. Check for loose connectors
and reseat all internal connectors.
<<Charlie's comments on foc.. |
| Purple blob - or worse>>