This article is going to cover a very common problem with cathode ray tube (CRT) monitors.  This issue is often discussed but rarely properly fixed or addressed in complete form.  We’re going to cover all aspects of this issue and help you diagnose and hopefully fix your monitor purity issues.  Parts of this article may be a little technical, but continue reading as there are some easy fixes included…

What is purity?

CRT monitors are additive color systems, meaning that all colors are created by adding a percentage of primary colors together.   These primary colors are Red, Green and Blue.

White = ( R:100% +  G:100%  + B:100% )

Black  = ( R:0% +  G:0%  + B:0% )

Red = ( R:100% +  G:0%  + B:0% )

Green = ( R:100% +  G:100%  + B:0% )

Blue = ( R:0% +  G:0%  + B:100% )

If your monitor exhibits any one of the following impairments, you have a problem with purity

In the neck of each CRT is a primary color electron gun.  The electrons are directed up/down and left/right by way of a magnetic coil located at the base of the CRT glass.  When an image can be displayed in perfect geometry and color, the CRT is considered to be calibrated  as pure.

The best example of purity is displaying a full screen of each primary color.  If each color can be displayed perfectly square (4×3 on standard CRT) and without color splotches, then the CRT is calibrated correctly (for that region of the world) and that there are no environmental impairments affecting the direction of the internal electron guns.  Purity is adjusted by moving the location of the windings used to redirect the electron gun beams (yoke).  More on this later.

What is Convergence?

Convergence plays hand in hand with purity in creating an image of expected color and with perfect alignment.  We know that each color is controlled by a separate electron gun.  Each gun is located in the neck of the CRT, but not in the same location.  So slight adjustments need to be made so that each gun illuminates the same exact location on the CRT to create a single pixel element.

Here is are a couple examples of very poor convergence.  You can also see the distinct primary elements.

Ok, so now what?

So, how did we get here anyway?  Why would my monitor look like this?

Simple Fix Convergence

First, let’s start with convergence problems.  Convergence is set and locked in place in the factory.  Arcade games typically get man-handled and relocated every couple years to new locations.  Operators are not usually very gentile with these machines and sometimes the glue which holds the yoke in place comes loose.  Sometimes convergence can easily be fixed by re-centering the yoke with the rubber wedges and gluing it back in place.   If that doesnt work, it is possible the  convergence rings were broken off or knocked out of position.  They too are glued in place and if they havent broken off, can be easily be slid back in position.  The manufacturer usually aligned these and marked them with ink or glue so relocating them back should be very simple.  If they have broken off, you will need to look into having this corrected by a professional or replacing the monitor (which is probably your best course of action).

Simple Fix Purity

All monitors have a purity fixer built in.  It’s called a de-gausser.  Most all  monitors have built in de-gaussing circuits that automatically run every time a monitor is turned on.  However, this only happens when a monitor is COLD.  So, if you are seeing this problem, shut off your game and wait about an hour.  When you turn it back on, you should hear a funny twang sound.  That is the degauss circuit attempting to rid the picture tube of unwanted magnetic interference.

Sometimes, when relocating an arcade game, the monitor will pick up stray magnetization.  Try running the automatic degauss circuit a couple times.  If the splotch has not been corrected, you may be one of what we call “the 1%”

Environmental Fix Purity

Sometimes, you have to adjust for environmental conditions that cannot be fixed.  You may have an I-beam in the wall or ceiling that is locally augmenting the Earth’s natural magnetic field.   Sometimes, it is in the ground below you.  Either way, this too can be overcome.

First, relocate the machine to another part of the room OR turn the machine temporarily 90 degrees.  Re-run the automatic degauss circuit a couple of times and see if this condition goes away.

If it works, then you have 2 choices:

1)  Relocate the machine or turn it 90 degrees.

2)  Compensate with magnets

Magnet Fix Purity

Ok, so we don’t love this solution because it is a trial and error solution, but it works – and nobody ever knows to do this.  This method also requires a little dexterity and risk of electric shock.  So, if you are not familiar with electronics or qualified for working with high voltages, please find someone who is.

First, you need some thin flexible magnet material.  Not too strong, typically fridge magnet strength.  A strip of flexible magnet can be purchaed in Home Depot or a craft section used for making picture frames etc.

The idea here is to use the magnets  on the back side of the monitor to compensate for the area that is not pure.  Experiement by moving the magnet along the back side of the glass tube.  The closer to the center (yoke), the more compensation.  Turn and spin the magnet until the blotch goes away and then glue the magnet in place.

You may see other magnets already glued in place by the factory.  Use that as a guide for size and location.

Again – do this with the monitor OFF and wait 15 minutes between each attempt so that high voltage is discharged.  Do all adjustments to the monitor in the position where the game will reside or you’ll be chasing your tail.  

If you have any questions, please comment on this article

So, how do you know when your monitor is ready to be replaced?

The Obvious

Ok, so your monitor wont turn on.  This could be for a number of obvious reasons.  Check these in order:

1. Look for something that may have damaged the monitor.  Many times an overhead marquee light fixture will fall and damage the tube, neckboard or chassis board.  If you don’t see any large parts lying around, you’re probably safe
2. Does the rest of the game work?  Is the overhead marquee on?  Are there any LEDs blinking on the game board?  Do you hear any sound when you insert a credit or press Player 1 Start?
3. Power is going to the monitor.  Check the main fuse.  This is sometimes located on the floor of the arcade game.  One or more fuses will supply power to the rest of the machine.
4. Check the fuse on the monitor.  Every monitor will have a small glass fuse located somewhere on the main chassis board.  Make sure the entire game is unplugged before you start poking around.
5. Make sure the video cable is plugged in and all wires are connected.  (Red, Green, Blue, Black and White

User Adjustable

Ok, so the monitor works, but it doesn’t look right.  There could be some simple adjustments to check first.

Check if your monitor had a wired remote control board.  It is usually about the size of an open matchbook and tethered to the main monitor board by a 24-36″ cable.  You need to understand the controls in order to adjust the monitor.  Most all of the following controls will be located on the wired remote control, however some may be located on the main chassis pcb.

Horiz Hold:  Use this to adjust the picture if it is rolling left / right.  If this does not work, check to see if the white wire is properly connected on the video input.

Vert Hold: Use this to adjust the picture if it is rolling up/down.  If this does not work, check to see if the white wire is properly connected on the video input.

Horiz Size: Use this to adjust the width of the picture

Vert Size: Use this to adjust the height of the picture

Horiz Pos:  Use this to adjust the position of the picture left/right

Vert Pos: Use this to adjust the position of the picture up/down

Bright: Use this to control the overall brightness of the screen.  This is in conjunction with the contrast.   First set the contrast in the middle. Adjust the brightness up all the way until the black image area is no longer black.  You may need to turn down the lights to fine tune this.  Then adjust the contrast up/down so that the colors aren’t too bright and washed out.

Not So Obvious

This is the grey area where a monitor works, but not even close to the way it should.  Unfortunately, many used arcade resellers leave their monitors in this condition and crank up the brightness and contrast to compensate.  Often this results in washed out colors.  Usually RED is the most obvious color of a tired monitor if the color bleeds onto other graphics.  Additionally, many arcade resllers rejuvenate their monitors to fix this issue.  This is a process of introducing high current into the tube to burn off deposits from the guns.  This actually works for a short time.  Sometimes for only hours, sometimes for months.  Either way, long enough to prove to someone that it looks good enough to sell.  This is unscrupulous behavior in my opinion, but you get what you pay for.  The problem is that there is no good way to tell if a monitor has been rejuvenated until it’s too late.   In this event, you’ll need a new monitor.

Repair or Replace

We can take your old monitor and give you credit for a fully rebuilt monitor (given it is the same or similar model and not physically damaged).  All of our monitors come with guaranteed clean CRTs with very low hours.  We rebuild all the typical wear components on all circuit boards and calibrate the monitor so that all color guns aim true.  Call or email us for detail.