RGB Monitor Adjustment

[Pyronious]

I recently purchased a Japanese sit-down JAMMA cabinet (the Neo Candy 29). It has a 29" Hitachi arcade monitor in it.

When looking at color bar test patterns (such as the service menu color bars in the Capcom CPS2 games),  I am not seeing some of the darker shades of color. They show up fine on the PC, but the arcade monitor just draws everything below a certain brightness as black.

For example, if there are 16 shades of red, the darkest 4 shades aren't visible at all -- they are just black.

For the most part the monitor image looks fantastic -- whites are bright and clear, etc.

On the front of the monitor are RGB Gain controls and a brightness control. Tweaking these makes the image brighter and darker but does not reveal the hidden bars of color.

On the back of the monitor are RGB "BKG" controls as well as "Drive" controls for I believe G and B (it's two of the three anyway).  Toyed with these a bit and was unable to reveal the hidden bars of color.

In the attached image, the shot on the left is what I would expect to see. The middle shot is what I actually see.  The shot on the right is what happens when I tweak with the R "BKG" control.

Can anyone give me any tips on how to adjust an RGB monitor?  I don't even know what some of these knobs actually do electrically. I understand black point and white point but I don't know how those relate to the controls available on this monitor.

If I decided to replace the monitor, where could I find a replacement?  WG doesn't seem to make a 29" Universal Mount monitor.

Pictures of the machine can be seen at my web site (http://www.pyronious.com).

[RandyT]

I guess the first thing I would say is, if the monitor looks "fantastic" you might just want to ignore the test and be happy.  You would only be sacrificing some of the subtle dark shades that probably aren't all that important to the games anyway.

You should also keep in mind that a PC monitor and an Arcade monitor are two very different beasts.  One sure way to understand this is to look inside each one of them.  A good PC monitor can have as many as 3 circuit boards inside that are responsible for digital controls, geometry, focus, color, digital convergence and just about everything else that is important to an accurate picture.  An arcade monitor will usually only have the most basic of adjustments and perfection is low on the list, with cost being more important.

This means that, compared to a PC monitor, the image will only ever get to just a certain level.

So I guess what I'm trying to say in a round-about way is that it may just be that way.  I have seen a number of monitors that seem to have poor "gamma" (might not be the correct term).  Meaning that they were nice and bright and the blacks were solid as well, but the scale seemed to be off on the shades. Mostly I have seen this on small tubes that have been rejuvenated, but large tubes with "cheap" circuitry might lack the granularity to achieve the subtle shades in the low end.

Then again, I might not have a clue and it could just need a cap  

*EDIT*
BTW, don't mess with the BKG controls.  That will just mess with the background and turn your blacks into colors you don't want.  Brightness and contrast are the controls you are after, but if you are at the end of the range, there may be an internal limiter that can be adjusted.  There is also the possibility that a slight increase of the HV adjustment on the flyback could help, but I would avoid this as it can cause other than healthy levels of XRay radiation to be generated by the tube.

RandyT

[Pyronious]

OK.  Although the whites look great I am not happy with the loss of the lower shades, and it is significant enough to make some games appear too dark and a somewhat difficult to play.

I'll keep looking for information on how to adjust this correctly.

I understand that the "brightness" control should allow more of the lower colors to appear, but instead it just does this:

[kspiff]

Do you have a large POT labeled screen?  That might help a bit, just don't crank it too high.  You might have to readjust the focus knob a bit, too, if you turn it up..

My monitor has the same issue, but I don't consider it to be too big of a deal.  I can only really notice it in 3D fighting games, and with those it *always* seems either too bright or too dim on an arcade monitor :/

BTW, the focus and screen controls are usually mounted to the chassis towards the back.

If you already tried this.. I've no ideas

[Pyronious]

I can't seem to find a "screen" pot.  I have the following controls on this monitor:

R/G/B Bias (neckboard)
R/G/B Gain  (front-panel)
R/G Drive (neckboard)

I have a good understanding of what the RGB Gain controls do, but the Bias and Drive are pretty much a mystery to me.

[Edgedamage]

Hi the screen pot is on the flyback transformer. Most if not all arcade monitors I have worked on have the focus and the screen controls on the flyback.

[Pyronious]

Okay, I've looked at the main board that has the large transformer on it and found 2 pots that are mysteriously labelled in Japanese.

Pot 1 is near a place on the board where all the major adjustment pots (brightness, v/h hold and position, etc.) would be if they weren't moved to a breakout board as they are on my monitor.

Pot 2 is tucked away near the large high voltage transformer I presume is the flyback.  I can't really show it in the picture because it's difficult to get an angle on without removing the monitor.  It is also mysteriously labeled in Japanese.

Based upon your experience, which one do you suppose is the "screen" pot?

P.

[Edgedamage]

Ugh great show me a monitor I never seen before! Ok if there is no pots on the flyback the "big black thing with the red wires" my only suggestion is get a friend and have him sit in front of the monitor and adjust one pot at a time until you get the right pot. Also when adjusting unknown pots you should think of a clock face so when you have to adjust the pot back to where it was just remember "I started at 10:00" Hope this helps.