dim mvs monitor

Is there a way to repair a dim monitor (brighten the picture) without replacing it? I was told its dim because of age.

At the risk of looking biased (I think this is one of my cabs we are talking about)Here is a Usenet posting by Randy Fromm, who is generaly considered to be the authority on arcade monitors and troubleshooting them:

BRIGHTEN UP YOUR DAY
A Simple Modification Makes Picture Tubes Brighter!
By Randy Fromm

When you have an old monitor, it's sometimes difficult to get the picture
as bright and sharp as you'd like it to be. No matter how you fiddle and
tweak the adjustments, the picture looks dim and/or out of focus.

The culprit here is probably the picture tube (the CRT) not the chassis
of the monitor. You can verify this by trying the chassis on a good
picture tube. If it works okay, the CRT is at fault.

Before you throw the picture tube in the trash, here are a couple of "last
ditch" things to try to restore some usable life to the CRT and save some
bucks. You can take the picture tube (or the entire monitor, although
just the CRT is required) to a local TV repair guy who has a "CRT
Rejuvenator." He can connect the CRT Rejuvenator to your picture tube (it
connects to the pins of the CRT in place of the monitor's neck board) and
"shoot" the tube. The CRT rejuvenator works by increasing the voltage to
the CRT heaters, making them glow extra hot and bright. This causes the
"cathode" in the electron gun to emit more electrons.

Then, the momentary pulse of a high voltage capacitor discharge is
placed between the cathode and the nearest "grid" of the electron gun.
You can see a visible spark in the neck of the picture when this happens.
The resulting arc will blow away the crusty layer that is covering the
cathode and expose fresh cathode material (barium oxide.) The newly
exposed surface will produce a much better stream of high-energy
electrons, resulting in a much clearer and brighter picture.

HOWEVER . . . There is about a 50/50 chance that the CRT rejuvenation
process will completely ruin the electron gun. Don't do this until the
CRT is otherwise unusable. The TV repair guy will probably warn you about
this beforehand. If the CRT is bad, you've got nothing to lose and
everything to gain. The process takes only a few minutes, so he shouldn't
charge you more than $10.00 for the job. If he won't do it for that, call
around and try to find someone who will.

Cheep-o Tube Brightener

Here's another last ditch CRT brightener. Once again, this has to do with
brightening (and heating) the CRT heater in the electron gun. The CRT
heater is driven by an output winding on the flyback transformer that is
in the high voltage unit. Just a few turns of wire is all that is
necessary to develop the low voltage required to operate the CRT heaters.


The CRT heaters are designed to operate on a steady 6.3 volts AC.
Because the output of the flyback transformer is actually short pulses
instead of a continuous AC voltage, the pulses are around 20 volts or so.
It averages out to be the same. The short pulses create the same heater
brightness (and heat) as the continuous 6.3 volts AC.

When a monitor manufacturer selects a certain type of high voltage unit,
they will often find that the output voltage of the CRT winding on the
flyback transformer is a bit too high for the picture that they're using.
A resistor will be connected in series with the CRT heater to cut down
the extra voltage. It will be a low resistance; typically around 2.2 ohms
or so.

It's easy to find this resistor. On the schematic diagram, follow the
wires back from the CRT heaters. One side of the heater is usually
grounded. The other side connects to the resistor (if the resistor exists,
that is.) If the other side of the heater goes directly to the flyback
transformer, you don't have a resistor in series with the CRT heater.

If you don't have the schematic diagram, you can probably follow the
traces and wires back from the heater pins of the CRT. They will usually
be labeled with the letter "H" on the monitor's neck board. If not, use
your meter set to the lowest resistance scale (ohms) and check for a low
resistance between two pins of the CRT (power off.) These will be the two
heater pins. You will see only an ohm or so between the two pins. Try
pins 9 and 10 first as these are commonly used for the heater connections.


Now that you've located the resistor, short it out. Just solder a piece
of wire across the resistor on the bottom of the board. With the resistor
eliminated from the circuit, the heater voltage will be boosted up a bit.
You'll probably notice the increased brightness of the CRT heater and a
brighter, sharper picture as well. If the CRT heater is too bright (like
glowing yellow/white) you may want to replace the existing resistor with
one of half its value instead of shorting it out completely.

And here is Randy Fromm's <a href="http://randyfromm.com/" target="_blank">web page</a>

[ September 03, 2002: Message edited by: Briggs ]

[ September 03, 2002: Message edited by: Briggs ]</p>

Does it help if you turn up the screen volts slightly, thats the lower pot on the flyback tx. It will brighten the pick, if you go too far you will see retrace lines.

If the crt has low emmission you will notice low contrast as well as brightness, also may affect the focus resulting in a blurred pic.
Usually one gun will go down before the others ie lack of R, G or B.

Often find a combination of all of the above if your CRT is on the way out.