Wednesday, November 23, 2011

Washed out picture

If you can obtain a full intensity raster by varying the brightness or screen
control, then your problem is most likely in the video amplifiers or power
for the video amplifiers.

If, however, the screen control varies the brightness but will not get
a bright raster, you probably have problems either with the HV power supply
or the filament supply for the CRT - is there the normal bright orange
glow at the base of the CRT? If it is dim or very reddish, there may
be a marginal connection or bad component in the filament circuitry.

Ghosts, shadows, or streaks in picture adjacent to vertical edges

Complaints about these kinds of problems are very common especially as
the screen resolution and necessary video bandwidth keeps increasing.
Most are due to cable and video termination deficiencies and not actual
monitor defects.

The video signals for red, green, and blue (or just a single signal for
monochrome) are sent over cables which are generally 75 ohm transmission
lines. These are coaxial cables that may be combined inside a single
sheath for VGA, SVGA, MACs, and many workstations but may be separate coaxes
with BNC (or other) connectors for other video applications.

Without going into transmission line theory, suffice it to say that
to obtain good quality video, the following conditions must be met:

1. A good quality of cable must be used. This means one in which the
characteristic impedance is close to the optimum 75 ohms, one which has
low losses, and one which has good shielding. For installations
using BNC connectors, a good quality of 100% shielded RG59U is often used.
The BNC connectors must be properly installed or they will contribute
to mismatch problems.

2. Where multiple monitors are to be connected to a single video source,
all wiring is done in a daisy chain fashion. The only taps permitted
are the minimum necessary to connect each monitor to the chain. This
usually means a BNC-T connector or a pair of connectors on the monitor
for each video signal. T connections with cable must be avoided.

3. Only the last monitor in the chain should be terminated in 75 ohms. All
of the others must be set to Hi-Z. Monitors with BNC connectors will
usually have one switch or a switch for each color to select termination.

Monitors for PCs, MACs, and workstations usually have built in
termination and do not offer the choice of Hi-Z. This means that without
a video distribution amplifier, it is not possible to connect multiple
monitors of this type to a single video source with any expectation of a
good quality display.

Failure to follow these rules will result in video ringing, ghosts, shadows,
and other unsightly blemishes in the picture. It is often not possible to
control all aspects of the video setup. The cable is often a part of the
monitor and cannot easily be substituted for a better one. The monitor
may not have properly designed circuitry such that it degrades the video
regardless of the cable and display board quality. The display card itself
may not have proper drivers or source termination.

Ironically, the better the video card, the more likely that there will
be visible problems due to termination. This is due to the very high
bandwidth and associated signal edge rates.

Some examples of common termination problems:

* Overly bright picture with trails following vertical edges, perhaps with
periodic ringing. This is due to a missing termination. Check if the
monitor is set for Hi-Z instead of 75 ohms. If there is no switch, then
the termination may be faulty or the monitor may need an external resistor.
For BNC connectors, plug-on terminations are available.

* Bright ghost images adjacent to vertical lines. This may indicate that
the terminating resistor is greater than the impedance of the cable.
You may be using Ethernet Thinnet cable by accident which is RG58 with
an impedance of 50 ohms.
* Dark picture and ghost images adjacent to vertical lines. This may indicate
that the terminating resistor is too low - multiple monitors on a chain all
set for 75 ohms instead of just the last one. Or, an improper type of cable
such as audio patch cord.

* Fuzzy vertical edges. This may indicate a poor quality cable or a run
which is just too long. For high resolutions such as 1280x1024, the
maximum cable length may be as short as 25 feet or less for poor quality
cable. Better cable or fiber-optic repeaters may be necessary.

* Other similar problems - check cables for defective or improperly installed
connectors. This is especially applicable to cables with BNC or UHF type
connectors which require a kind of artistic talent to assembly properly and

If only 1 or 2 colors (of the R, G, and B) are effected, then look for
improper switch settings or bad connections (bad cable connectors are really
common) on the problem color cables.

Intermittent, flickering, or missing colors

This is a catch-all for some of the most common monitor problems. Most of
the causes boil down to bad connections of one form or another. However,
defective components like bias resistors on the CRT driver board or in the
video circuitry could also be at fault.

* Does whacking the monitor have any effect? If so, then bad connections
are confirmed. If the color(s) come and go suddenly, then it is most likely
*not* a CRT problem. The bad connections could be at the VGA cable, video
driver board on the neck of the CRT, or elsewhere (see below).

* 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 monitor. 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

Possible causes of intermittent or missing colors:

* VGA or other video input cable. Sometimes these develop intermittent
problems at the connector to the VGA board. These may be internal
to the cable in which case it will need to be replaced or if you are
handy and have infinite patience, you can replace just the VGA connector.

Alternatively, the male pins of the cable may not be making good contact
with the female VGA socket. First try contact cleaner. If this does not
work, gently squishing the male pins with a pair of needlenose pliers may
provide temporary or permanent relief if the pins are a tad too small.
However, if you go too far, you can damage or break the pins or cause the
female socket to become enlarged and loose fitting for any other monitor
you may use.

If this just happened after reconfiguring your system and reconnecting
the monitor or installing a new monitor, check your video connector - you
may have bent over or pushed in pins 1, 2, or 3 - the R, G, and B video
signals respectively.

If you find a bent pin, ***carefully*** straighten it with a pair of
needlenose pliers. If it is pushed in, try to grab onto it and pull it
out - then put a drop of Epoxy or other adhesive at its base (don't get
any on the part of the pin that makes contact) to prevent it from being
pushed in again.

There may be cold solder joints on the VGA board itself at the VGA
connector. These can be resoldered.

* 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 monitor usually around the pins of
large parts such as transformers, power transistors and resistors, and
internal connectors. Inspect with a strong light and magnifier if

* Internal connectors that need to be cleaned and reseated. Remove,
clean with contact cleaner, burnish, and replace.

* Bad filament connections inside the CRT (gradual fade in and out or
one filament not lit). Replace CRT or monitor.

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 but it could be in other
parts of the video circuitry.

* 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 circuit/chip that is working (i.e., a color
that appears on the screen) to *all* three color drivers on the CRT neck

- If you now get a more-or-less black and white picture (there may be a
moderate color tint as the relative intensities of R,G,B may not be
balanced), the problem is likely with the circuitry on the mainboard.

Note: the picture will be the intensity of only one color channel so it
will not be quite *normal* in any case.

- If you still have missing or messed up colors, the problem is on the CRT
neck board or with the CRT.

Psychodelic color

The means colors that are not normal and that adjustment of the user
controls is not able to correct it so that all colors of the picture
are properly displayed at the same time. For example, you are unable
to get any yellows or blues in picture that should have these colors.

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

* Confirm that the input is not a weird color video - try another software
program or video source. We have a draftsperson who always sets up his
Windows color scheme in this manner - we keep wishing it is the monitor
as **that** could be fixed!

* Verify that this is not a missing color problem - one of the primary R, G,
or B, has disappeared. If so, refer to the section: "Intermittent, flickering, or missing colors
* If this is a monitor with BNC connectors and you are using them, make sure
you had the video termination switches set correctly (75 ohms if this is
the only monitor or the last monitor in a daisychain; HiZ if an intermediate
monitor in a daisychain.) A very common cause of unbalanced or blooming
colors assuming the monitor itself is good is incorrect settings of the
* A bad connection, bad component, or short circuit in the video circuitry
or CRT neck board could also result in strange colors.