This is a catch-all for some of the most common TV and monitor problems.
|NotTaR of Television Sets : Intermittent or missing colors
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.
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Note that due to the additive color scheme used in all emissive color displays
like CRT or flat panel TV sets and video monitors, a single missing primary
color (red, green, or blue) will result in the following appearance (for a
Missing Color Appearance
Red Cyan (blue-green)
Green Magenta (reddish-purple)
Which color is affected may be even more obvious if the set has a color
on-screen display for which you recall the proper colors.
- If gently whacking the set can make the color(s) come and go suddenly, then
bad connections are probable. The most likely place for these are solder
pads on the little circuit board on the neck of the CRT or even dirty CRT
socket pins that are not making solid contact. Try prodding the CRT neck
board with an insulated stick to see if you can affect the colors.
Although not impossible, this is not likely to be a CRT problem.
- If the color fades in and out with a delay of about 10-15 seconds, it is
probably intermittent power to the CRT filament for that color and probably
means a bad CRT since the three filaments are wired in parallel inside the
CRT. One of the internal connections has come loose.
Look in the neck of the CRT to make sure all three filaments are glowing
orange. If one is out or goes on and off, toss the set. Replacing the CRT
is probably not worth it. However, if they all go on and off together (all
colors would be fading in and out though perhaps not quite in unison), then
bad connections for the CRT filaments on the CRT neck board are indicated.
To narrow down the problem:
- Locate the output for the bad color on the video driver board on the
neck of the CRT. This will probably read a significantly higher
voltage than the corresponding pins for the good colors. A circuit
problem is likely - probably on this board.
- Test components on this board for the good and bad color channels. A
shorted transistor or open resistor can kill one channel. Swap parts
between good and bad colors to confirm.
- Gently pull the CRT neck board off of the CRT and replace it. This will
tend to clean the contacts.
- Connect an output of the video/chroma circuit/chip that is working (i.e.,
a color that appears on the screen) to ALL three color drivers on the CRT
Most of the causes of intermittent colors boil down to bad connections
of one form or another. For totally dead colors - not intermittent - bad
components are also a possibility.
- Printed circuit board on the CRT neck. This is a common location for
cold solder joints. Check with a bright light and magnifying glass
for hairline cracks around the pins of larger parts. Prod and tap with
an insulated tool to see if the problem is effected. Resolder if necessary.
- Cold solder joints elsewhere in TV or monitor usually around the pins of
large parts such as transformers, power transistors and resistors, and
- Internal connectors (including CRT socket) that need to be cleaned and
reseated. Remove, clean with contact cleaner, burnish, and replace.
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