Stuff you need to know
RGB CUT OFF: I like to say that this is the “canvas” upon which the game board then will draw the graphics (using the RGB GAIN/DRIVE channels) by pushing RED, GREEN and BLUE in the amount and mixture needed to get all the colours used by the game’s palette. CUT OFF = The background colour. These pots are on the main chassis under the front of the screen.
RGB GAIN/DRIVE: Using these channels the game board can produce any colour it needs by mixing the amount of each together. Anything from one single red dot, fill the whole screen with white or nothing at all = black (if the RGB CUT OFF is correctly tuned). GAIN/DRIVE = The foreground colour. These pots are on the remote board inside the door with the coin mechanism.
Conclusion: The CUT OFF is like a lamp screen and the GAIN is the colour of the light bulb.
One *could* say that the formula used to show a picture on a CRT screen looks like this:
Video = (Colours pushed out from the game board x GAIN/DRIVE) + RGB CUT OFF.
If the CUT OFF for example has the GREEN turned up a bit too high, the whole screen will be out of the colour balance “sweet spot” all the time, even when the game board isn’t pushing out any green on the RGB GAIN/DRIVE. For example if the game board was showing a completely white screen, it would have a light green tint.
One other important factor to consider with the EGRET II monitor tube is the “anti glare” coating which has a magenta tint. Some EGRET II private owners prefer to remove this coating as scratches on the tube surface will “light up”. This will show the true colour of the tube, that is green. So if you fine-tune your video picture to perfection, then remove the coating, the screen will again need to be readjusted as the basic conditions has been changed. The GREEN CUT OFF will most likely have to be adjusted as the green tint of the tube glass would affect the balance otherwise.
It’s best to do these adjustments in a dark room.
01. Boot up a game that has a nice TEST MODE. A grid and colour bars where the contrast is clear so you have “steps” in the bars. PGM or CPS2 games for example. For my example below I’ve used the grid from Do-Donpachi.
Note: If you plan on using a CAVE SH3 board, don’t forget that those games have a built in contrast/brightness in the TEST menu, if so, make sure that those settings are set to neutral (defaults) or all of your other games will need adjusting.
02. Open the back door to get easy access to the SCREEN and FOCUS pots that are situated on the flyback (that black block on the monitor chassis) and also lift up the hood that holds the bezel so you have access to the chassis situated pots under the front of the tube
Note: If you’re comfortable around your monitor you can reach these pots from the front door (right above the PCB mounting board). Reaching up from the front door is much better in my opinion, as you can see the results right away in front of you. Especially for the FOCUS setting. I suggest you get acquainted with where they are situated with the power off. It’s not dangerous, but when you are nervous around hot electronics you tend to make mistakes, and that often leads to stuff breaking. Safety first.
03. Start up your cabinet and bring up a grid in the TEST MENU and then let the chassis warm up for 15-20 minutes
04. On the remote inside the coin door, turn all of your RGB GAIN/DRIVE pots all the way down, and put the BRIGHTNESS pot in the midnight/neutral position
05. On the chassis under the front of the tube, turn down the RGB CUT OFF pots to a neutral postion (50/50)
06. Now adjust the SCREEN pot on the flyback until the screen is totally black (you want to go just past the last trace of the grid
07. Turn each RGB CUT OFF pot up until you see the black space around the white grid turn into the colour you’re adjusting, then turn it down until the black is perfectly black again
08. Adjust the RGB GAIN/DRIVE controls on the remote board until the grid is really white without bleeding out/turning blurry
09. In the game’s TEST MENU, select a COLOUR test picture instead of the grid (you want columns of RED, GREEN and BLUE and a contrast/brightness column (shades from black to white) then adjust each colour’s GAIN/DRIVE until you get the brightest, yet sharpest setting (for the colour) and also the white in grey-scale column sharp and bright
Tip: The “sweet spot” for the RGB GAIN/DRIVE is when the white and the first grey have the same glow up close but when you back away from the screen clearly are distinguishable from each other – WHITE and GREY, side by side.
10. Take a final look at the grey scale column to make sure that there is no tints of RED, GREEN or BLUE – adjust if needed
11. Adjust the FOCUS pot on the flyback on the chassis to ensure maximum sharpness
If you have succeeded in following this guide, you will have a picture that has pure blacks and sharp RGB graphics. Enjoy!