How to Correctly Set Up Monitor Colours and Brightness

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Colguide 1 picture.jpg

This looks terrible. Here's how to fix it.


  1. Learn where the RGB cutoff and gain, brightness and contrast, and screen pots are on your monitor chassis.
  2. Install a PCB into the cabinet, power on and let the monitor warm up for 15 minutes using the PCBs test screen mode. Use something that has a grid and colour bars on the same screen, as this provides a good brightness mid-point.
  3. A darkened room. As little ambient light as possible.

Tools Required

  1. An insulated screwdriver or plastic tool suitable for adjusting the chassis pots.
  2. A torch of some description.
  3. Eyes. Just one will do, but two are ideal. Each must be connected to your own optic nerve.


The example below uses a Nanao MS8 chassis as it's a good base for the theory. The idea is to get the colours as bright as possible without any bleeding, with clear gradient steps stretching to a pure black background. Notes on other chassis are found at the end.


To begin with you need to set the pots to a sensible default. You want a completely blank slate. Set the following to their lowest position:

  • RGB cutoffs (sometimes labelled "background")
  • RGB gains
  • Brightness
  • Contrast

Your pots may have a notched "middle" position that you can feel when they're turned, if they do you may want to set them to this as a default. With experience you'll understand how the various settings interact on your chassis - for example if your gains don't go high enough having the contrast at more than zero will help with this. It should never be set high though, if that's required you've done something wrong.

Don't touch the screen pot yet, do that in the next step.


Set the screen pot so that the picture is entirely black, just where the visible (raster) lines disappear.


Colguide 2 raster lines.jpg


Colguide 3 black.jpg


Turn the brightness pot up to its middle position. If there's no notch estimate where the middle is.

Colguide 4 brightness.jpg

RGB Cutoffs

Turn these up one by one until the gradient stretches all the way across for each colour. The last bar should be fully black, and the one immediately next to it should be barely visible. Make sure that the true black areas of the screen are still 100% black - study the display up close and personal if you have to.

  • If the cutoffs do nothing except change the colour of the whole screen, turn the gains up to their middle position as a default.

Red cutoff

Colguide 5 red cutoff.jpg

Green cutoff

Colguide 6 green cutoff.jpg

Blue cutoff

Colguide 7 blue cutoff.jpg

RGB Gains

The gains are used to alter the cutoffs, and you will need to switch between both of them to adjust them correctly.

  1. Turn up the colour gain until the two brightest colour bars are virtually the same shade when you're about 30cm away from the screen, yet distinctly different when you're a metre away. Typically this is at the middle of the pot.
  2. Turn up the cutoff to bring the dark shades back up to the level they were before you adjusted the gain, again ensuring that black is still perfectly black.

Red gain and cutoff

Colguide 8 red gain.jpg Colguide 9 red cutoff 2.jpg

Green gain and cutoff

Colguide A green gain.jpg Colguide B green cutoff 2.jpg

Blue gain and cutoff

Colguide C blue gain.jpg Colguide D blue cutoff2.jpg


  • Toei TC-A252S: Requires gains to be set to middle default.


You should now have a marvellous on screen image. If your monitor is normally under tinted glass and you've removed this to adjust it, you may want to make a further boost to the brightness pot once it's back under glass but if doing so make sure that black is still black!

Note that all pictures in this guide are representative and do not reflect how your screen will look exactly. It's extremely difficult to photograph a CRT monitor accurately!