Monday, November 21, 2011

One color is too weak or too strong

If the problem is slight and/or has gradually gotten worse, this may just
require an adjustment of the color brightness/background/bias and/or color
gain/drive controls inside the monitor. See the section: "Brightness and color balance adjustment

Even if it appears as though there is an excess, this may actually be a
reduction in one of the primary colors. For example, a magenta tinge is
represents a reduction in the strength of the green signal.

* Too high an intensity for one of the color channels will result in a tint of
one of the primaries: red, green or blue.

* Too low an intensity for one of the color channels will result in a tint of
the complement of one of the primaries: yellow, cyan, or magenta.

* Problems mainly in the shadows or dark areas of the picture usually represent
a fault with brightness/bias/background.

* Problems mainly in the highlights or bright areas of the picture usually
represent a fault with the gain/drive.

A color that that is now suddenly brighter or darker than normal resulting in
incorrect color balance or a tint in the background could be due to a number
of causes:

* Bad cable or pin bent on cable connector.

* Bad connections or bad component in video amplifier or on CRT neck board for
that color.

* Weak gun in CRT (reduced color).

* Bad video card or incorrect software color map settings.

* For monitors with sync-on-green capability, the monitor may think you are
using sync-on-green when in fact you have separate sync. In particular,
this may result in a problem with excessive green:

(From: Bob Myers (

Some monitors provide a user-selectable setup option for "sync-on-green"
vs. separate syncs. Sometimes, this doesn't really change where the
sync itself is coming from. In those cases, it's automatically detected
but *does* change where the reference level for the video is expected
to be. You might try checking this setting, if you have it, and changing
it back and forth to check the effect. It's not likely to be the problem
in a separate-sync system like a PC, but weirder things have happened
and it's easy and cheap to check out.

No color - black and white picture

This means absolutely no color - equivalent to a black and white picture.
Not even a hint of color.

If you are using a composite video input, troubleshoot the chroma circuitry
like you would a TV - see the document: "Notes on the Troubleshooting and Repair of Television

This is an extremely unlikely failure mode for a computer monitor
unless you are using a composite video input. It is most likely to
a software driver or program problem. Sometimes, the PC will think that
the monitor you have connected is not capable of color and certain programs
will then display in B/W no matter what.

In some cases this is due to an initialization problem - possibly a race
condition during the boot process - especially likely if you are using an
older video card with a new fast processor.

First, confirm that the source is actually in color - try the monitor on
another computer or vice-versa.

Check the settings of any mode switches - in rare cases there is a color/mono
switch or button.

Note that to the average person, the obvious question becomes: is my color
picture tube bad? The answer is a definitive NO. It is virtually impossible
for a defective CRT to cause a total loss of color. A defective CRT can
cause a lack of a primary color - R, G, or, B which will mess up the color
but is not likely to result in a black and white picture.

Brightness control has no effect

The following assumes that the picture is fine but the brightness is
fixed - probably at too high a level. However, there could be several
interrelated problems if a common supply voltage were missing, for example.

If it is a knob, then it should be varying the control grid (G1) voltages
relative to the cathodes (K) of the CRT. This is not likely to be a very
complex circuit. If you do not have a schematic, I would start by tracing
from the control, check continuity and solder connections. Check the
control itself for proper operation with an ohmmeter. A power supply going
to one side of the control (negative probably) may be missing. Tbe control
grid voltage will end up on the little board on the neck of the CRT - check
there as well for bad solder connections or open resistors.

If brightness is a digital control, then you will need a schematic unless
there is an obvious bad connection.

Blank picture, power light on

Does 'blank picture' means a totally black screen with the brightness and
contrast controls having no effect whatsoever? Or, is there is no picture
but there is a raster - light on the screen? The direction in which
troubleshooting should proceed differ significantly depending the answer.

Verify that you computer has not simply entered power saving mode and
blanked the screen or shut off the monitor video and power circuits

Confirm that the video source is not defective or blank - try another one.

Here are some questions:

1. Is there any light on the screen at any settings of the brightness
and contrast controls, and/or when switching channels. Can you see any
raster scanning lines?

2. Can you obtain a raster of any kind by adjusting the screen (G2) control
(probably on the flyback) or master background or brightness?

3. Looking in the back of the monitor, can you see the glow of the CRT

4. Do you get that static on the front of the tube that would indicate that
there is high voltage? Any cracking or other normal or abnormal sounds
or smells?

If the answer to all of these is 'no', then you have a power supply and/or
deflection problem. Refer the the section: "No picture but indications of power".

Possible causes of no raster:

* No or low high voltage (low voltage, deflection, or high voltage power
supply failure).

* Fault with other voltages like G1 or screen (G2) to CRT.

* Filament to CRT not getting powered.

* Drive to CRT bad/shut off as a result of fault elsewhere. For example,
failure of the vertical deflection may disable HV or blank the screem to
protect the CRT from burn-in due to the very bright horizontal line that
would result. With some monitors, it is possible that the X-ray protection
circuitry will blank the screen.

Possible causes of no video: problem in video input, video amplifiers, video
output, cutoff due to other fault.

It could be as simple as a bad connection - try gently prodding the boards
with an insulated stick while watching the screen. Check for loose connectors
and reseat all internal connectors.