The picture is still barely visible but very gray, with retrace lines. I can adjust the brightness but it will only go brighter. If I adjust the contrast the retrace lines will fade but the picture is no longer visible.
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Check the screen voltage. Adjust it to a little lower and check. Check the supply voltage to its video output stage [CRT base card]. If this voltage is less than normal, this kind of fault can occur. Check the smoothing capacitor [the electrolytic capacitor of low capacitance value] is bad. If it is bad, the voltage stated above will go low,and the retrace lines will be visible. Check these.
The fault you now see is technically called vertical retrace lines with picture. The above said are the main causes for this.
If you wish to get some details; check the site linked here. Viewing it in "Mosaic" will make surf easy. Surf the site with patience. http://electronicshelponline.blogspot.com/ Pull up older posts.
The faint background lines are vertical flyback lines. Start your diagnosis by turning the brightness and contrast controls to minimum and view the screen in a darkened room. If you can now see a raster with horizontal lines visible then it is likely that the tubes A1 screen voltage is excessive. The screen voltage is usually within the range of 400v to 600v. Adjustment for this is often part of the flyback transformer. Check all high value resistors
in the screen and focus circuitry. Some of these reistors may be
built into the flyback transformer. As the picture gets brighter the beam current increases, this will eventually cause the X ray protection circuits to trigger shuting off the set. A fault in the video drive circuits to the cathodes of the tube will cause similar symptoms but usualy results in a predominance of one colour, ie
bright red, blue or green raster with flyback lines.
This fault can occur to mainly three reasons. ABL circuit failure. Low screen voltage or lack of emission from picture tube cathode. Just advance the screen voltage to a little, and observe the result. Screen control can be located on its Line Output Transformer [LOT]. there will be two variable controls built on to LOT marked as screen and focus. Screen control will be at lower side, and focus will bw on the top. Just advance [clockwise movemnt] to a little, not more, advance it till retrace lines are just visible on the screen. Before doing this, set all the picture controls, contrast, colour and brightness of the TV to zero. Once the retrace lines[thin horozontal white lines across the entire screen at about 1 inch distance with each other]; are visible, stop there, turn the screen control counterclockwise to just a point when these lines are just goes off. make this adjustment in a dark room so that you can set this point very correct. After this check the perfomance of the picture. If this does not help you, ABL circuit should be checked for any fault.
If emission of the picture tube has got down, even the screen adjustment said above won't help you. The only way is to replace the picture tube with same type and number. OK.
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1. Turn the green
screen control on the Focus Block until retrace lines appear and gradually turn
it back Until the point where
you can see the retrace line disappears, just before cutoff. 2. Turn the red screen
control on the Focus Block until retrace lines appear and gradually turn it
back Until the point where
you can see the retrace line disappears, just before cutoff. 3. Turn the blue
screen control on the Focus Block until retrace lines appear and gradually turn
it back until the point where
you can see the retrace line disappears, just before cutoff. 4. If the
screen still appears too bright after proper G-2 adjustment, you need to adjust
the sub-bright adjustment in the service menu control down
until screen cut-off. (Service data Range is usually 21 to 25 in the Service menu, for Sony
sets you first go to category "MCP2", & then adjustment item 01(
"SBRT")= subright. For electrical the focus, put on the screen a
clear picture of your choice thru an input of the TV set from a DVD, then pause
the playback of the DVD Look into each color and rock that color focus control
back and forth (turn the control one way then the other way slowing down as the
picture goes into the best focus. till the picture looks sharp do each color
till they all look in focus. NOTE: it is best to look into each color
tube to achieve the best electrical focus.For optical focus please follow the manual lens adjustment in the sets
service manual By Larry
Those are retrace lines, the screen controls which are a technical control located under the front gray panel of your tv needs adjusted. This also could be an indication of a bigger problem, most common would be the focus block failing. it could also be of the picture tubes failing but this is not as common or possibly the crt driver ic's. There are specific diagnositc steps to preform to isolate the potental failure. this could lead to the tv going very bright then shutting down. The first thing a tech is going to do is to adjust the screens and leave, somtimes this is enough, but sometimes it is not. if you want to try and adjust the screen i have an instruction set below, but i must warn you that there are high voltages present when attempting this adjustment and can be dangerous if you are un familure with tv repair.
Turn your color all the way down and the brightness in the middle, then
find the focus block, it will be a block with 6 controls one row will
say screen the other will say focus near the picture
tubes, adjust the screen controls(one control for each color) until the
picture has a good black and white look to it, then turn your color up
and it should look fine. This is how i balance out the picture. But
there is another method that allot of techs use, the other method is to
adjust the brightness up until you see what is called retrace lines it
is a jagged line going down the screen, once you see these lines back
the adjustment down just until they disappear. Do this for all three
colors. This method works but on an older set can throw the white
balance off because of tube wear.
Where only one color is showing, suspect an incorrectly adjusted individual background/bias control or bad part on the CRT neck board for that color.
Individual brightness/background/bias control(s) - mark setting of pot for the problem color and then see if a slight adjustment removes the retrace lines. See the chapter: "TV Adjustments". Of course, if this happened suddenly, the problem is not due to a misadjusted control though a dirty pot is possible - turn it back and forth - this might clean it and restore normal operation.
Component or connection on CRT neck board - insufficient voltage to or incorrect biasing of the video driver for this color can result in the CRT never totally blanking. Compare voltages and signals, and swap components between good and bad channels to confirm.
Blanking circuit - this may be a part of the video/chroma chip or separate. Check and compare waveforms of good and bad colors to determine if the blanking pulses are making it to the video output.
There is a slight possibility that a bad CRT may result in visible retrace lines. To eliminate this possibility:
Disconnect the filament - all evidence of a picture, raster, and retrace lines should disappear once the filaments/cathodes have cooled (15 seconds or so. If there are still visible retrace lines, the CRT is suffering from cold or field emission from someplace (may not even be the cathode).
Turn down the screen (G2) control on the flyback (usually). If one color remains no matter how you set the control, again there is some kind of weird emission from the CRT. However, if white/gray retrace lines remain, the problem may be in the screen supply.
You will be greatly helped if you have a schematic for your TV set, and you may need to change some parts, clean some connector contacts and/or tweak settings inside the set, so remember the original settings before you tweak them...
The screen voltage adjustment should be on the back of the high voltage multiplier. It should be marked as "Screen", or "G2". Next to it, is the "Focus" adjustment.
Some models of Sony sets have two focus adjustments. This is for H and V focus.
When increasing the screen voltage will usually increase the wear factor of the electron-gun assembly in the CRT. This is because it is increasing the screen bias current.
When increasing the screen bias, the brightness will increase a little. When the CRT is weak, this may produce visible retrace lines more so than on a good working CRT. This is because the excessive screen current will stop allowing the electron-gun assembly to work at its proper cut-off level in order to allow the blanking drive to bias it off during the retrace period.
Increasing the screen bias will usually cause a shift in the colour temperature especially in the low level gray colours. This is because the AKG reference for the electron-gun biases will be offset due to the differences in the electron gun performance characteristics change.
The front panel normally has some screws that need to be removed from the inside of the set. You need to remove the back cover first and you should see the screws. Then the panel pops off. Good Luck