I have a 27" Toshiba Cinema Series tv set I've been working on, the problem is a dark picture, the High Voltage is where it should be and it appears to have plenty of Screen Voltage Range, I suspected a video problem, and replaced the Video Detector IC with no luck, at this point I have no idea where to look next, any ideas?
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There are two small holes on the rear side through which you can adjust focus and screen. Use a flash light and locate the two adjustable slots inside the holes. This part carries high voltage. Do not use a metal screwdriver to adjust. Put the TV facing a mirror so you can see how it works. Do not turn more than 1/8th of a turn. The focus control makes picture sharp or fuzzy. Screen control could change brightness. While watching the picture in the mirror, slightly adjust the screen control. Do not turn too much. If it doesn't work, then call a JVC authorized repair center.
Dark picture? hmm. meaning there is no brightness variation, assuming this is the fault I think U might be having low screen voltage. Check for high value ( around 2W) resistor, preferably from 100K to 680K on the "C" board or neck board. Post back Rifaa
If you promise not to touch the wrong thing, you can adjust the
screen and focus knobs on the high-voltage transformer (what we call
the flyback). Do you see the big red wire going to the CRT tube?
That is the anode lead of the high voltage (around 25,000 volts).
The thing that it goes to on the circuit board has 2 little knobs
coming out the back of it. Try adjusting those (use a tool with
insulated handle if you please) to increase the brightness and improve
the focus. When the screen adjustment is all the way up and it is
still too dark - then its time for a new TV.
this problem is due to
1 not proper voltage on crt terminals
2 check video output supply voltage
3 check luminance section of chroma ic
4 if tv is very very old than there is a possibility of crt getting weak
If the picture is fading slowly out it could just be a cold solder connection on the ctr board or the Hi voltage circuit that supplys the filiment voltage to the crt. To check this you have the back off and when the pic goes out you look at the crt to see if its still lighting up. if its not then you gotta find out where your missing the filiment voltage at> If there is still a light inside the tube when the picture is dark then it could be a PIP problem or in the video section /video jungle IC on the set. Now these sets have alot of high voltage inside them even when the sets unplugged so I advise against going inside and tweeking with the set unless you know all the safty issues with the Hi voltage and storage capacitors inside this set. there are no real user serviceable parts inside these sets and should only be serviced by a quilified service person. Good Luck