please help me with my crt tv

[steve612]

hello

this is the first day i tried to connect a jamma board to a crt tv and i am very proud i did it:)
works perfectly, but the problem is that some parts of the image are missing:(
here is a picture  http://i47.tinypic.com/ajndqc.jpg

i tried to change the ratio from 4:3 to 16:9 but it can't show the image right. i dont know...

what can i do for that?
thanks very much

[mgb]

Does the Tv have any adjustments for picture size. I know alot of tvs are typically overscanned so the picture is a bit bigger than the screen.
What are you using to convert rgb to an input to the tv? does it have adjustment?

[steve612]

thanks for the reply! unfortunetly there is no adjustments for picture size:(  ony ratio 4:3 and 16:9
i am in europe so jamma to scart and it has no adjustments.. only some resistors for typical reasons...
i don't know what to do

[rCadeGaming]

I'm not familiar with that set, but adjusting the geometry should certainly be possible.  You need to get the model number off the back and then find a service manual for it online to find out how.  Depending if it's an analog or digital chassis, you will either have to open up the case (learn about discharging the tube first!!!) and adjust some potentiometers, or get it into the digital service menu by connecting a jumper or putting in a special code on the remote.

[matsadona]

Well, this is quite common. The good thing is as you already noticed the perfect picture in terms of colors etc.
But since all arcade games have more or less variations in resolution and (horizontal) frequency, a perfect geometry is very rare without tuning.
As mentioned before, what you need is access to the service menu. Hopefully there are settings for HOR SIZE, and HOR FREQ (or similar).

[apfelanni]

google the tv type and find out what kind of chassis it uses , or open the backplastik and make a snapshot . maybe its a grundig cuc chassis , analog poti or digital osd based. 

[steve612]

unfortunetly i can't change any settings and i cant find the service menu in the net i searched everything:(

[rCadeGaming]

did you get the model number off the back of the set and search "(model) service manual"?  Keep digging, I'd be surprised if you can't find it.

[apfelanni]

here are some service codes for " schneider " tvs . what is the problem witch checking  the tv backside for a modell or chassis number ?? btw . the picture looks a little bright and blurry . guess u have to adjust some input levels . most cheapass chassis ( like beko ) are not handling offspec signals very well.

http://www.reparaturtipps.tv/diverses/marken/schneid.htm

[rCadeGaming]

the picture looks a little bright and blurry . guess u have to adjust some input levels . most cheapass chassis ( like beko ) are not handling offspec signals very well.

I think arcade boards usually put out a hotter signal than NTSC/PAL standards, I'd put some 220uf capacitors on the RGB lines to smooth them out, as well as some 100 or 200 ohm pots to tweak color levels.

[steve612]

i personally like the colours, i put 82ohm resistors in front of rgb lines

[rCadeGaming]

Just because the color looks good now doesn't mean that it can't be improved with $3 worth of trimmer pots.  These will let you individually tweak the brightness of red green and blue on the fly.  You might not know the optimum picture until you see it.

This kind of old analog hardware rarely put out perfectly balanced color levels.  For example the Super Nintendo (mine at least, could vary between systems, and TVs especially) looks decent at first; but when you get into it, you realize that the blue is a little stronger than the green, and the red is way stronger than either of them.

One good way to measure color brightness is to look at the width of the scanlines (the black spaces in between the colored lines) around different colors.  The scanlines in areas that are supposed to be pure bright green should be the same width as the scanlines in pure bright red.  Using a test pattern for this is best, but not always possible. 

On the SNES, the letters on the Mario World title screen are a good reference as they are large areas of pure red, green, and blue.  In my case, the scanlines between green were huge, the ones between red were almost non-existent, and the ones between blue were in the middle.  This indicated that green was weak and red was way too strong.  I left the pot for green all way up, turned down blue a tiny bit, and turned down red a lot.

Just be sure you're not using color areas for reference that are supposed to be mixed or dimmer colors, and keep an eye on the overall tint and where you want it as well.

Is this a little over the top?  Well yeah, and the difference isn't night and day; but I do think it's worth spare change in parts.  It's noticeable once you know what you're looking for, and it's fun to adjust.

[steve612]

Thanks for the information!

[rCadeGaming]

Hey, I've since found a much better method of equalizing the colors than just comparing scanline width.  First, focus only on red, and set it to go a good level.  This depends on your preference.  You can make it as vibrant as you want, but you will be able to see when it's too much as subtle difference in shade blur together and it will bleed over onto neighboring areas.

Then look for something that's intended to be pure yellow.  In terms of light, pure yellow is an equal mix of red and green.  So, now that red is set, adjust only green.  When there is too much green, yellow areas will have a green tint.  When there is too little, they will have a red tint.

Finally, look for something intended to be pure white, which is equal parts red, green, and blue.  Since the other two are set, finish by adjusting only blue.  When there is too much blue, white areas will have a blue or "cool" tint.  When there is too little, they will have a yellow or "warm" tint.  Some people may prefer a cool or warm tint, but I just set it as neutral as I can.  Pure white means the colors are well balanced.

[steve612]

I have placed 3 potentiometers of 1 kΩ in front of 3 colours, and i adjusted the picture. Thanks for the help. I found out that puting more resistance in front of the colours, the screen minimizes a little but not to much as I wanted.