Category Archives: CRT to LCD – right and wrong

Arcade: using an LCD instead of a CRT

Part 1 – debunking other peoples work, as I would like to be debunked

I saw this video from TNT amusements:

As you can see, they swapped the CRT for an LCD. They use a converter board to get the 15kHz to 31kHz and in that process scale the image in the converter and in the monitor(1280*1024). They did this for one of their customers. I am unsure as to the result of this operation, mostly due to these statements made in the video:

1) They will install a brand new LCD monitor
2) They claim the image is crisp and clear.
3) They offer it as a service

So, I went and found that exact LCD monitor, the same converter PCB and since I do not own a Moon Cresta PCB, I used my Frogger which uses the same resolution.

lcd1

lcd2
The Dell monitor is from 2006. This is somewhat old in LCD terms. I got the monitor for 10 USD. Like my SCI project below, it has a resolution of 1280*1024 and a ratio of 5:4. The converter board does not output in this resolution, so you have to choose one of the available resolutions in the menu and then let the monitor scale that to its native resolution. This can have drastic effects on the image quality, especially in games with thin 1 or 2 pixel lines. These can jerk around when they disappear and reappear as they move.

The monitor itself is extremely slow and is rated at 25ms. I know these values are highly subjective, but the number is from the manufacturer’s own specs. I tried running Terra Cresta on it, to see what a scrolling game would look like. Results are jerky movements and tearing.

Setups:

lcd3

lcd4

Running this test I got pretty nice colors. The picture quality was overall okay, but a little soft. Nothing that I would have a great problem with. However, the excessive blurring of moving elements is completely unacceptable. The frog(or ship in Terra Cresta) is completely blurred out when in movement. When it comes to Moon Cresta I suspect that the black background and being a fixed shooter will combat tearing but then again, bright space ships against a dark backdrop must look horrible when moving.

Here is a short video, please note this is recorded of the screen. Keep your eyes on the ship.

Since there are two parts to this setup, the converter and the monitor, I have tried another LCD monitor with the converter. In this case, an LG 22″ TV. The results were far better, but still not great. Installing an LCD screen in your arcade demands a fast monitor. These days 16:9 screens are 99% of the market, but there are still a bunch of 5:4 1280*1024 monitors being made, mostly for business and writers. These monitors go for about 200USD. One can only wonder what the image quality would be like if one of these(5 ms or lower) has been installed in the Moon Cresta from the video.
I tried the setup one last time with my 27″ AOC LCD monitor which is stated as having a response time of 2ms, and it is leaps and bounds better than the two other monitors.

My final conclusion is: The setup seen in the TNT video is completely unacceptable. I would have a hard time finding anyone who would think this image quality is OK. You need to find a fast LCD monitor for this to work, and it probably will never look right with a game like Moon Cresta. The monitor used by TNT is unsuited for any kind of gaming.

 

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Part 2 – scaling at its best…doubling (or the like)!

First of all: I know this will be frowned upon by many readers. But please try to follow my thoughts. Maybe it is possible to implement an LCD monitor in a classic arcade machine, in this case my Special Criminal Investigation(SCI from here on out). I got this machine years and years ago, with graphics problems. At that time I did not know anything about PCB repair and while SCI is an okay game, I like the prequel, Chase HQ, a lot better. So, I decided to remove the original PCB and use PC emulation. The inside of the cabinet never got to that point of tidiness that I like, so recently I decided to go back and give it an overhaul.

This is when I decided to give the LCD idea a try. I have always been a ‘CRT-guy’, not from arcades really, but from CRT projectors. I still use a Marquee CRT projector daily, and the choice of changing a tube monitor to a flat panel does not come easy. But these days I try to keep a more open mind than I used to.

Going into this project I had some concerns/demands/wishes. Let me put them in a bullet point list.

1) No stretching of the image in any way.
2) How will rescaling be done, and can it be acceptable?
3) Lower total-weight of the machine
4) Less heat
5) Less reliance on old parts, especially dangerous parts

The first point mentions stretching. I have a Cruis’n World (with the original CRT), and I see a lot of people put 16:9(1.78:1) TV’s in their driving cabinets. When these guys do this, they stretch the image from 4:3(1.33:1) to 16:9(1.78:1) which is 100% unacceptable to me. If they do not strecth the image, the image will probably be smaller than the original monitor due to the format and width of machine. I remember of friend of mine having a Sega Model 2 cabinet(I think), in which he put a vertical 16:9 LCD. He turned on Galaga while I was there, and it was horrible, just horrible. The problem is, you cannot get 4:3 LCD monitors in these sizes.

SCI and Chase HQ run 320×240 resolution. The 5:4(1.25:1) LCD monitor I ordered have a resolution of 1280×1024. This works out awesome, since 1280/320=4 which gives perfect scaling. No guessing, just multiply by 4. On the ‘line’-side(to stay in old-land), the game has 240 lines. 1024/240 = 4.27 which is not very even scaling. But if we instead do this: 240*4 = 960 then we get perfect scaling again, but leaving a small black bar in the top and bottom of the screen, which also gives you the 4:3 picture! And that is it! It cannot be better than this. Imagine off-scaling like this: You have two lines, one is black the other is white. Scale that to three lines; you have to flip a coin to decide if the third line should be black or white. Doing even scaling, no guessing is required.

I weighed the items. The CRT + chassis came in at 15.5kg, the LCD at 3.5kg. This makes the already insanely heavy cabinet 12kg lighter. I have not accounted for the Hantarex US250 power supply in the bottom yet, which is, of course, also gone.

I know that nobody has been injuried greatly from the anode cup or otherwise, from working on CRT chassis. However, these CRT pcbs are getting older and older, maybe pushing 25+ years. Also, how many people have worked on the chassis before it reaches you? Should this be cause for concern, or at least cause for concern for the next guy when you have worked on it?

All these points lined up, and I took the plunge. I am not the type of guy that forces himself to like something just because he has it, so I will be completely honest.

Image quality:
Very, very nice. Nice strong colors and good blacks(CRT-guy, remember?). Does the image actually warrant an ‘upgrade’ from CRT to LCD? No, they are on par. Colors and precision goes to the LCD, slightly. Everybody will love the image from the LCD.

Cabinet-feel:
I get a bit worried with myself about my connection with curved CRT’s in arcades. I just expect to see that curved screen when I stand near an arcade machine. It is not bad on the SCI, but on more classic machines, it really pops out at me. Not in a horrible way, but just a gut feeling that something is wrong. I once saw a picture of an arcade machine with an LCD running Pac-man, and my mind could not handle seeing the maze un-curved. It looks absolutely crazy, but it is, of course, right. The maze should have perfect geometry. Of course a picture should be flat, and CRT TV’s in homes has been flat from the mid-90’s. That is 20 years! However, not all cabinets will look right with an LCD. I think that older machines with the screen almost lying down, and the graphics bezel ‘try’ to surround the picture, but fail because of the curve. Would such a game, like Galaga, be so bad if the LCD was all the way up to glass and going to the sides of the bezel? This is more difficult on games where you have the glass close to the players face.

Picture of SCI with LCD.

sci1

I also need to address the problem of changing a CRT for another CRT. You can get into a lot problems with a new tube. I think about that plastic bezel that often surrounds the tube, and follows the curve of that exact tube. I have tried several times where I needed to discard the plastic bezel after a tube swap.

So, can my SCI project be translated to other games? Well, that depends. I saw a Youtube video where a couple of guys put an LCD in a Moon Cresta. Now, being a PC monitor, it starts at 31kHz but the game board is 15kHz. The resolution of Moon Cresta is 256×224 and the monitor is 1280×1024. 1280/256 = 5 and 1024/224 = 4.57. Pretty uneven scaling. So, let us do as before and use 4. 256*4 =1024(of the 1280) and 224*4 = 896. This will leave black bars all around the image, and it will not be doable in their setup. What they do is: They use a converter that takes the 15kHz RGBS from the original PCB and outputs 31kHz VGA(RGBHV). At the same time, it scales the image, but the device does not have the resolution of the LCD. This means that they scale the image in the converter and then again in the LCD. I would love to see how that image looks in real life. *I have one of these converter units on order to test it*

The main question must be: one of these years I am going to get a Galaga. My favorite game of all time. Could I put an LCD in that? No, I could not. I think Galaga would suffer a lot from off-scaling. If Galaga was 320×240, like SCI, then maybe! But it is not. These games with very fine, straight lines do worse compared to games like Out Run and maybe Neo Geo games. But for games that has resolution that you can multiply up, think about it! Consider it.

As a final note, I also feel that some games deserve to be kept original more than others. Donkey Kong is more a piece of arcade history than SCI. Same goes for Galaga compared to Cruis’n World. I love Cruis’n, but it is really just a racing game. And what about the future? Maybe when OLED TV’s comes about, we can have those curved since they use no backlighting, like LCD uses fluorescent or LED to light up the panel.

sci2

Picture of free space where the CRT used to live.
/Nicholas