I would start by making some voltage measurements on the signal processor IC to see if the black level pin voltage can be varied. if not that might be the issue, but I have a feeling that it will vary so lets look at what else could be wrong. I know I harp on this circuit so much, but I have seen its failure so many times that I suspect it when ever HV issues occur. Inside of your TV there is a circuit that is supposed to shut the TV down whenever there is excessive HV pulses coming from the HV output of the IHVT (flyback transformer) if this circuit fails there will be an excessive amount of HV delivered to the anode of the picture tube, and this would cause the picture to become too bright. In addition this could be caused by a failure in the HV/Horizontal section of the TV in question. I would begin checking waveforms and voltage levels in that section if the brightness control on the signal processor IC is indeed working but not controlling the black level of the picture. I can not tell you what components are bad, just that you should concentrate on the HV/Horizontal section and the shutdown circuit for measurements. Get a schematic. If you dod not feel comfortable doing this take the set to a qualified TV technician.
May 13, 2007 |
Durabrand DWT1905 TV