[TechAssist] FIXED!! Toshiba 28510, TAC9005 chassis, weird brightness problem
- From: Kevin <kevintv@xxxxxxx>
- To: TECH-ASSIST <techassist@xxxxxxxxxxxxx>
- Date: Fri, 19 Mar 2004 14:34:03 -0800
When the brightness is set to factory setting and the set is turned on
the picture is black and the video driver transistors on the CRT board
are maxed out at 216 volts. As I slowly increase the brightness,
increment by increment, the voltage decreases down to about 100 volts as
the picture gets brighter and brighter. With the picture at its
brightest and all washed out, changing channels makes the picture go
black again and then slowly brighter again!
I also found D866, a 30 volt zener, in the power supply that was shorted
and supposed to be causing "blooming" problems. I replaced it with no
difference that I could see. I guess the other problem overshadows this
blooming problem!
I also replaced IC501, the jungle IC, and ICX01, the digital converter
IC with no change.
Finally with the help of another tech we noticed that the sub-brightness
control was not working. The trace leading back from the middle leg of
the control had a minute break. Even after scratching the green off the
trace to reveal the copper, it was impossible to see the break except
under magnification (and then it barely could be seen!) What would
cause this type of break in the trace when everything "looks" good?
Enough to drive a technician CRAZY.
Kevin Wilks
Kevin's TV & Video Repair
Penticton BC Canada
kevintv@xxxxxxx
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