Modelines for NTSC Television and Component Transcoder

[Jason125]

Hey Everyone, really enjoyed studying every post to piece together the mystery of GroovyMame and VMMAKER.

I have followed the advice offered in various threads to build the following configuration:

Intel Core 2 Quad
Windows XP 64
ATI Radeon 4670 PCIe
GroovyUME 148u2
VMMaker 1.3c

Using primary DVI output, DVI-VGA adapter, connected to Crescendo TC1600
Component output connected to NTSC Sony Trinitron KV-24FS100. No secondary monitor.

My question is whether anyone has created a good modeline for either VMMaker or GM with this setup. I have tried using many of the examples posted here, finally settling on horizontal settings 55-65, and vertical 15200-16200 (see attached file). Many of the arcade settings begin with 49.5, which seems to be too low for NTSC televisions. The rest of the modeline is black magic to me. I can play with the h-front and back porch easily enough, but many of the vertical settings result in too much overscan (where the top and bottom of the ArcadeOSD test pattern are missing the top/bottom 1-3 rows). I have noticed that 224 modes work great, esp with 60 hz, but 256 modes often require adjustments to v-fp to settle.

Can anyone provide suggestions on making this "lock in" with native resolutions?  I would love to find the best solution possible with this configuration. Please let me know if it is unreasonable to expect perfect geometry with this as well, so I can adapt my expectations. I will post and test anything you need!

Thank you!

[mikecrj]

Hi, Jason125. I'm running a similar setup as you. I'm using a TC1600 with a Sony KV-20FS120 which utilizes the same BA-6 chassis as your TV. I use these monitor specs in VMMaker:

monitor_specs0 15625-16200, 55.50-61.00, 3.766, 4.842, 6.456, 0.192, 0.192, 1.024, 0, 0, 240, 480

monitor_specs1 15625-16200, 55.50-61.00, 3.766, 4.842, 6.456, 0.960, 0.192, 0.512, 0, 0, 256, 480

My TV can display about 238 lines (not the full 240 lines). The first monitor spec centers resolutions up to 240 lines and the second monitor spec centers resolutions up to 256 lines. So, if I were to play a game with 240 lines such as Captain America and the Avengers, I would lose 1 line at the top of the display and 1 line at the bottom. If I were to play a 256 line game like R-Type II, I would lose about 9 lines at the top and 9 lines at the bottom. If I were to play a game with 224 lines such as Street Fighter 2, I wouldn't lose any lines and there would be black borders at the top and bottom of the display.

These monitor specs center the picture horizontally and vertically based on the settings I've made in my TV's service menu. I use the default values as indicated in the service manual with the exception of: HSIZ 26; HPOS 44; VSIZ 30; VPOS 38; and PAMP 22. These settings may not be right for your TV.

I would first try these monitor specs in VMMaker, reboot, launch ArcadeOSD, display 720x480@60i (need to have added to ReslList.txt) and adjust your TV's HSIZ, HPOS, VSIZ, and VPOS until you can get the image centered as best possible. If your TV is like mine and does not display the full 240 lines, you will not see the full top and bottom borders, but you should see most of the horizontal borders.

If that doesn't seem to work, I would try the different "H center" presets in ArcadeOSD at 720x480@60i in conjunction with your TV's HSIZ and HPOS. You can then plug the "H front porch," "H sync pulse," and "H back porch" into your monitor spec line in VMMaker.  The VfrontPorch (0.192), VSyncPulse (0.192), and VBackPorch (1.024) should center resolutions of 240 lines vertically. Often a VfrontPorch of one line (0.064) is used, but I found that three lines (0.192) is necessary for my TV.

Also, in VMMaker make sure to set ModeTableMethod_XML = 2 to utilize magic resolutions in GroovyMAME. In GroovyMAME, I use these lines:

crt_range0 15625-16200, 55.50-61.00, 3.766, 4.842, 6.456, 0.192, 0.192, 1.024, 0, 0, 240, 240, 480, 480

crt_range1 15625-16200, 55.50-61.00, 3.766, 4.842, 6.456, 0.960, 0.192, 0.512, 0, 0, 240, 256, 480, 512

I hope some of this will be helpful. To be honest, I don't know much about the technical reasoning behind these settings. I spent a lot of time reading this thread: http://forum.arcadecontrols.com/index.php/topic,116669.0.html

I just recently got my TV and transcoder and I spent the better part of last weekend coming up with these settings. But now that it's done, all of the games are centered. Also, I've been playing with GroovyUME and getting excellent results with NES, SNES, Genesis, etc. Having only played these systems with composite cables in the past, they look incredible through the TC1600.

[Jason125]

Wow, that is the most clearly written, most helpful single post I have seen yet. I have spent weeks trying to get the right settings, not being certain if my expectations were too high with our config. I also have a 32-inch Trinitron, so will be interesting to see if it uses the same settings. Would you be willing to share your VMMaker and MAME files?

Do you have a decoder ring / service manual for the other settings in your TV?

Hopefully some of the great folks like Calamity or RCadeGaming can weigh in on this and help both of us understand or tweak these further.

Thank you!

[mikecrj]

I have attached VMMaker.ini and mame.ini. Note that I use g:\ in VMMaker.ini and d:\ in mame.ini. Make sure to use the appropriate drive letters for your configuration. You can find the service manual here:
http://www.4shared.com/document/7IcQrQ9D/2913233-SONY-KV20FS120-Chasis-.htm?aff=7637829

To access the service menu your TV must be turned off, then on the remote press Display, Channel 5, Volume +, then Power. Select items with the Channel 1 and 4 buttons and change data with the Channel 3 and 6 buttons. Save your changes to memory by pressing Muting and then Enter.

I used ArcadeOSD to make my horizontal and vertical adjustments. To center the horizontal, I used 720x480@60i and tried the various "H center" presets and then fine tuned my TV by adjusting the HSIZ and HPOS. I noted the "H front porch," "H sync pulse," and "H back porch" and then incorporated them into my monitor spec lines in VMMaker. I ran VMMaker again, rebooted, and then worked on the vertical adjustments.

To center the vertical I used two resolutions, one for 240 lines (256x240@60p) and one for 256 lines (256x256@55p). This is why I have two monitor specs. If I were to use just the first monitor spec, games with more than 240 lines would be cut entirely at the bottom with the top left intact. I prefer to cut an equal number of lines from the top and the bottom so that the image appears centered. Note when centering the vertical in ArcadeOSD, be sure to reduce the VSIZ on your TV to 0 so that all of the lines are visible.

In testing the 256x240@60p resolution, I started with a "V front porch" of 0.192 and a "V sync pulse" of 0.192. I then adjusted the "V back porch" until I found that a value of 1.024 cropped an equal number of lines from the top and bottom of the picture. I then updated my first monitor spec line in VMMaker with these three values.

In testing the 256x256@55p resolution, I tried the various "V center" presets until I found the one which cropped an equal number of lines from the top and bottom of the picture. I then updated my second monitor spec line in VMMaker with the values for "V front porch," "V sync pulse," and "V back porch."

I tested with Captain America and the Avengers as it is 240 lines and has text on the very top line ("1P" and "2P") and bottom line ("Credit"). I verified that my findings in ArcadeOSD cut an equal number of lines from both the top and the bottom. I then adjusted VSIZ and VPOS in the service menu until I maximized the viewable area on the TV. I then tested R-Type II and Mortal Kombat and confirmed that the image appeared cropped an equal amount from both the top and the bottom.

If you do not wish to cut any lines from the top, set VfrontPorch to 0.192, VSyncPulse to 0.192, and increase the VBackPorch from 1.024 in 0.064 increments (probably to 1.152). Then test Captain America and the Avengers to see if the top line ("1P" and "2P") displays fully. I remember having problems with the VfrontPorch set to 0.064 or 0.128. I was losing lines at the bottom of the screen in games with 232 lines (none of the image should have been cropped at that resolution). I found that a VfrontPorch of 0.192 was my minimal value which resulted in no cropping for those games (e.g., Elevator Action Returns).

[Jason125]

Mike,

Thank you so much for the detailed instructions. If I can get this going properly, I am not certain what I will do in those early morning hours, trying just one more adjustment. I hear sleeping is a good possibility!

What are you using for a front end, if any? Any other emulators on your system besides UME? I have an old Neo Geo cabinet that I'd like to adapt for an MAME system eventually, but getting the software portion completely working has taken so many months now. I love seeing everything come together, but I have a sneaking suspicion my wife doesn't share my joy when a modeline finally works at 2 am.

[mikecrj]

Jason, I have been working on the monitor specs in order to get the horizontal better centered.  However, I'm having problems with a few games.  For example, with donpachi (320x240@57.551), twincobr (320x240@55.500), and tdragon2 (384x240@56.000) the top border is off an inch from the top of the screen and the bottom is cut slightly.  These resolutions look fine in other games such as goldnaxe (320x240@60.054) or ffight (384x240@59.629), the difference being the refresh rate.  I think I could modify the vertical porch settings to get tdragon2 to display correctly as it is only 224 lines.  But I wouldn't know how to build an additional monitor spec in mame.ini because I'm not sure what is causing the problem with these particular games.  Other games display low refresh rates fine, for example I have mk, dbz, and kungfum at 55.500 Hz.  Also, these three games that are giving me trouble are all vertical games and I am displaying them vertically using the rotate_r command for orientation in mame.ini.  If anyone has any idea of what the issue may be, please let me know.  Thanks!

VMMaker.ini
monitor_specs0 15625-16200, 55.50-61.00, 3.202, 4.803, 6.938, 0.192, 0.192, 1.152, 0, 0, 256, 480

mame.ini
crt_range0 15625-16200, 55.50-61.00, 3.202, 4.803, 6.938, 0.192, 0.192, 1.152, 0, 0, 240, 256, 480, 512

[Calamity]

Hi mikecrk,

Let's see if I understand: the problematic games are run at their native resolution (full screen) so you are physically rotating the TV, or otherwise you are rotating the picture keeping the TV static?

[Jason125]

Calamity,

Unlike Mike, I am using the default settings in MAME to display vertical games on a 24-inch or 32-inch NTSC television, using the TC1600 VGA-to-Component transcoder. Could you please review the modelines Mike generously offered to see how we might optimize image quality with our configuration? Is it necessary to have 2 (or more) modelines to effectively display all resolutions on an NTSC-only TV?

Thank you!!

[mikecrj]

Calamity, yes I am running vertical games at their native resolution.  So for example, in donpachi "Player 1" appears along the right edge of the screen.  I don't physically rotate the TV, I just remap the controls so that left goes up, right goes down, etc.

Since my last post, I have begun to figure out what is happening.  With my monitor spec, as the refresh rate decreases from 60Hz, the picture is pushed down.  This leaves a black border at the top of the screen, the top of the image is not cut, but the bottom of the image is cut.  As the refresh rate increases from 60Hz, the opposite happens and the image is pushed up.  This was more noticeable with vertical resolutions of 240 compared to 256.

I added some resolutions with VMMaker and then adjusted them in ArcadeOSD so that the top line appears at the very top of the screen.  Here is what I found:

256x240, 54.918Hz, 15.597kHz (23-3-18 or 1.475, 0.192, 1.154)
256x240, 55.902Hz, 15.597kHz (18-3-18 or 1.154, 0.192, 1.154)
256x240, 56.922Hz, 15.597kHz (13-3-18 or 0.834, 0.192, 1.154)
256x240, 57.976Hz, 15.653kHz (9-3-18 or 0.575, 0.192, 1.150)
256x240, 58.962Hz, 15.625kHz (4-3-18 or 0.256, 0.192, 1.152)
256x240, 59.939Hz, 15.824kHz (3-3-18 or 0.190, 0.190, 1.138)
256x240, 60.999Hz, 16.165kHz (2-3-20 or 0.124, 0.186, 1.237)

256x256, 54.918Hz, 15.597kHz (7-3-18 or 0.449, 0.192, 1.154)
256x256, 56.006Hz, 15.682kHz (3-3-18 or 0.191, 0.191, 1.148)
256x256, 56.919Hz, 15.994kHz (4-3-18 or 0.250, 0.188, 1.125)
256x256, 57.627Hz, 16.193kHz (3-3-19 or 0.185, 0.185, 1.173)

I added multiple monitor specs to mame.ini, adjusting the vertical frequency range and the vertical porch settings.  I then tested those problem games that have a vertical resolution of 240.  They are no longer being pushed down, but now sometimes the horizontal is not centered and the image is being cut along the left side.  Also, sometimes the native refresh rate was not picked, but a lower refresh rate.

Am I on the right track?  If so, can you recommend some monitor specs given my findings?  By the way, I'm using a X600 XT and Windows XP 32-bit.  Thanks!

[Calamity]

I added some resolutions with VMMaker and then adjusted them in ArcadeOSD so that the top line appears at the very top of the screen.  Here is what I found:

256x240, 54.918Hz, 15.597kHz (23-3-18 or 1.475, 0.192, 1.154)
256x240, 55.902Hz, 15.597kHz (18-3-18 or 1.154, 0.192, 1.154)
256x240, 56.922Hz, 15.597kHz (13-3-18 or 0.834, 0.192, 1.154)
256x240, 57.976Hz, 15.653kHz (9-3-18 or 0.575, 0.192, 1.150)
256x240, 58.962Hz, 15.625kHz (4-3-18 or 0.256, 0.192, 1.152)
256x240, 59.939Hz, 15.824kHz (3-3-18 or 0.190, 0.190, 1.138)
256x240, 60.999Hz, 16.165kHz (2-3-20 or 0.124, 0.186, 1.237)

256x256, 54.918Hz, 15.597kHz (7-3-18 or 0.449, 0.192, 1.154)
256x256, 56.006Hz, 15.682kHz (3-3-18 or 0.191, 0.191, 1.148)
256x256, 56.919Hz, 15.994kHz (4-3-18 or 0.250, 0.188, 1.125)
256x256, 57.627Hz, 16.193kHz (3-3-19 or 0.185, 0.185, 1.173)

Beautiful. It seems that somebody finally figured out the Sony TVs

It's been frustrating all this time when people reported their issues with vertical centering on Sony TVs, I knew it couldn't be random but unfortunately I don't have one to test and nobody ever came up with a simple but comprehensive report like yours.  However I don't know if this will apply to other models.

Well, this is what is happening: when padding lines are required to achieve the desired refresh at a given frequency, GroovyMAME adds the half of them to each vertical porch. This guarantees vertical centering for arcade monitors. But Sony TVs (and probably others) work in a different way. It seems that the back porch must be constant, and padding lines need to be added to the front porch only. According to your report, once the 60 Hz boundary is reached, the behaviour must be the opposite.

This would require to add a new option to the modeline generator for this special case, quite a simple thing to implement. You may try to do it by dividing the specs into multiple ranges and it may work to some extent, but it's not a good solution and you can't guarantee that the right range is picked all the time.

[rCadeGaming]

Hopefully some of the great folks like Calamity or RCadeGaming can weigh in on this and help...

Hey, just saw this.  I hadn't been on in a while.  I'm guessing you already know that I'm using a KV-27FS120, which is also chassis BA-6.

Sounds like you guys are already figuring it out, but the biggest general tip I can give is that you need to have a rock solid understanding of how the CRT actually works and what you're really adjusting.  I mean how it is physically scanning the lines onto the screen, what the h and v sync pulses do, horizontal and vertical scan rates, and how all of these are controlled by active pixels/lines, front porch, and back porch  values.  Then on the computer side, learn exactly what EVERY number in a modeline represents, and what the graphics card's pixel clock is/does.  Get on the Googles.

Knowing all of these things makes adjusting geometry through modelines much easier, as its no longer such a process of trial and error, poke it and see what happens.  You will also be able to squeeze a LOT more adjustability out of these TV's.

Also, get more acquainted with the service menu.  Most of the important geometry setting will be in the DEF section near the beginning.  Always make adjustments using a test pattern.

In addition to MAME, my TV is also set up for consoles (real hardware).  So, I have my service menu geometry adjusted to a happy medium for the common ~224p resolutions from older consoles.  I've found this is great for MAME as well.  There are a ton of games that run around 224p.  To fit a few more lines, adjust overscan, etc, you can get some vertical size adjustment using a combination of horizontal scan rate and total horizontal pixel adjustment.  To fit in something a lot taller, like 256p, there is an interesting behavior of the TV that can be exploited.  If you increase the total lines (total, not active) to over a certain value (288 in progressive I think, haven't played with it in a month or so) the picture will snap to a much smaller size, and a much larger resolution will fit on-screen.  If you find this value in ArcadeOSD, you'll literally see a huge change in size as you cross over it.  256p games now fit very well. 

For example, I can switch between Street Fighter II (224p) and R-Type (256p) with no service menu adjustments, and have the exact amount of overscan I want in both.  This works the same with interlaced resolutions (the boundary value is the same amount of lines per field, or double that amount per frame), and I have my desktop running in 704@512i, to make Windows a little more manageable.  So my tip is to learn to how use these two different "pictures sizes" above and below this total horizontal line value.  Optimize the smaller picture size for 224p, and the larger size for 256p. 

A real console, like a SNES or Genesis will provide a good reference for a standard "224p picture size" to shoot for when adjusting the service menu.  I also use a PS3 to output test patterns in NTSC standard 480i.  Using a PC isn't the best point of reference to begin with because your modelines can vary all over the place.

Also, be sure you're getting the vertical scan rate as close to the original game's as possible.  These TV's work with a VERY wide range of vertical scan rates, I've pushed it down into the forties.  If you find that you're starting to lose picture, it may not be because the vertical scan rate is too high or low.  It's more likely that you're pushing the horizontal scan rate too far in the process.

[Calamity]

Knowing all of these things makes adjusting geometry through modelines much easier, as its no longer such a process of trial and error, poke it and see what happens.  You will also be able to squeeze a LOT more adjustability out of these TV's.

I completely agree rCadeGaming. These numbers are not black magic, they have a very real purpose, and the maths behind are quite simple. It's very gratifying to learn how it works.

To fit in something a lot taller, like 256p, there is an interesting behavior of the TV that can be exploited.  If you increase the total lines (total, not active) to over a certain value (288 in progressive I think, haven't played with it in a month or so) the picture will snap to a much smaller size, and a much larger resolution will fit on-screen.  If you find this value in ArcadeOSD, you'll literally see a huge change in size as you cross over it.  256p games now fit very well.

 

Yes, I've heard about this before, and it's something that should be considered. I wonder if that boundary total lines value is constant or depends on some other variable like vfreq or something. If it's constant, then it would be quite easy to model it by doing two separate ranges as mikecrj is doing. I believe this was designed to make these TVs autoadustable when switching between PAL/NTSC frames.

So to properly model one of these chasis, we have to consider:

1.- Centering works by adding padding lines to back porch only if vfreq < 60 Hz, and to front porch only when vfreq > 60 Hz
2.- A jump in v-size happens at the 288(?)-line boundary

[rCadeGaming]

The NTSC/PAL switching theory makes perfect sense.  I think the boundary is 288 lines, and I'm pretty sure it's constant, as I've used it with a few different resolutions of varying vertical scan rate .  I'll test to confirm.

[Jason125]

All,

Really appreciate your suggestions, and I promise I am trying to study up on the theory to understand what is really happening with each setting!

With many of the modelines generated with these settings, I noticed a strange curling in the top few lines, almost like a bowing (upper left and right only) in the top row of squares using ArcadeOSD using 256x240@60 as an example. When I adjust the dotclock manually down to 5.27 MHz, the bowing goes away! But then my vertical settings are 4-3-18 or 0.261,0.196,1.176 at 57.767 Hz. This does result in a perfectly centered picture, with clear borders seen on each side of the test pattern.

The complete line for this mode is 15625-16200, 55.50-61.00,4.557, 4.557, 7.596, 0.261,0.196,1.176, 0, 0, 240, 480

What component of the vertical or horizontal modeline causes the bowing to occur? Is the limitation in the Sony Trinitron (NTSC) CRT, or my settings?

Any updates regarding the 288-line mystery? I've tried going beyond this limit, but cannot settle on a good display afterwards.

Thanks!   

[rCadeGaming]

I think I owe everyone here an apology.

I got back to working on this stuff the other day and I realized that the two TV's I've been testing with CRT_Emudriver are actually KD-27FS170's.  I went back to a KV-27FS120 and I was not able to replicate this boundary value behavior.  I double checked, and it works consistently with both KD-27FS170's I have, but I could NOT get it working with either of my KV-27FS120's. 

Sorry about making empty promises here, and sorry if I sent you guys on a wild goose chase.

I worked through all the service menu settings on a KV-27FS120 for about three hours, but didn't get anywhere.  It just seems to start losing sync around 285 lines regardless of h and v scan rates, and from what I can see through the rolling image, the size change doesn't seem to happen at 288.  The strange thing is that both models are supposed to be chassis BA-6 according to the service manual, so I feel like there must be something I'm missing.  I also have some KV-24 and KV-32 models I haven't tried yet.

[machyavel]

For everyone's information, I think the 288 lines switch must be available on most pal capable TV. I have this behavior on my Philips (chassis anubis aac) and back in the 90s I could see it working on many TVs when plugged to a PAL console.

For example, to get rtype (which runs at Vfreq 55.018 Hz) inside the screen I set the Hfreq to 15845 kHz thus I get 288 total lines (15845/55.018= 288) so the overscan is switched off. There are even little black borders at the top and the bottom of the screen but that's still far better than the overscanned default display.

Now what remains problematic for me (since afaik, this tv has no service menu available) are the 240 lines games, when overscan is on I loose a few lines and when it's off the picture is shrunk too much.

[Jason125]

MikeCR,

Have you made any other progress with your modelines at or  above 256 lines? On my KV-32FS100 (BA-5D chassis) I was able to "cheat" a little using an option in the service menu, SCOR, which seems to shrink the lower portion of the picture so the entire 256-line image "fits". Granted, it's not native perfection, but it does work. You'd think I would be satisfied with this, but I am now trying your original specs to see if I can improve the native image a bit more.

Although my image on the 22-inch SVGA 31 KHz monitor is certainly better using the settings in another post, I keep trying to expand my knowledge using the Sony Trinitron TV image. Unlike an arcade monitor, it seems we really need to establish the CRT_specs for these NTSC-only televisions, especially as many people on the board have the advantage of using either SCART or PAL/NTSC monitors.

Dos anyone know if the CRT itself is limited to NTSC signals? There are service mode settings to change the mode from NTSC to PAL using the ID settings. Although the OSD indicates PAL-N, I am certainly not seeing 50 Hz modes working suddenly. I am assuming this only changes the menu options then?

Thanks for any update you can provide!

[rCadeGaming]

To fit more lines, you should just reduce VSIZ (VBOW and other setting may need to be corrected after changing, but start there).  SCOR needs to be set correctly so that objects appear to be the same size at the bottom or top of the screen as they are at the center.  Setting it incorrectly will cause a "warping" effect as things scroll vertically.

I believe that the ability to switch between an overscan and underscan mode lies in the chassis, not the CRT.  The tubes on my KD-27FS170's seem to be kind of crappy (geometry, convergence, and especially focus in the corners), so if I can't get them looking nicer with adjustments around the neck I'll be pulling their chassis's and trying them with tubes from my KV-27FS120's.  btw, I saw you mention focus on Trinitrons in another thread.  This requires a physical adjustment inside.  Check the service manual.

[rCadeGaming]

I worked through all the service menu settings on a KV-27FS120 for about three hours, but didn't get anywhere.  It just seems to start losing sync around 285 lines regardless of h and v scan rates, and from what I can see through the rolling image, the size change doesn't seem to happen at 288.  The strange thing is that both models are supposed to be chassis BA-6 according to the service manual, so I feel like there must be something I'm missing.

I just noticed that the service manuals for these models list both as chassis type BA-6, but they also have more specific chassis numbers which are different. 

KV-27FS120 - Chassis no. SCC-S61N-A
KD-27FS120 - Chassis no. SCC-S61Y-A

So, it is in fact a different model of chassis. 

I'm going to try driving a KV-27FS120 tube with a KD-27FS120 chassis (SCC-S61Y-A).

EDIT:  I had planned on trying to connect the KD-27FS120 chassis to a KV27FS-120 tube to get the best of both worlds (KD model has size switching, KV has excellent picture quality).  Upon taking it apart, I found that they actually use the same model of tube, so switching the chassis between them is no help.  The two models do also have slightly different driver boards, deflection yokes, and flybacks, so I also tried switching these around in various combinations (using the KV driver board and flyback with the KV chassis took a good deal of hacking things up), but couldn't get satisfactory results.

[cyb]

SCOR needs to be set correctly so that objects appear to be the same size at the bottom or top of the screen as they are at the center.  Setting it incorrectly will cause a "warping" effect as things scroll vertically.

Sorry to hijack a little bit, but I really wish I would've known about this a few years ago when I was using a 27" JVC Flat CRT. (model number AV-27WF36.)

 It had really nice picture quality but it exhibited the warping as you described. It drove me crazy so I quit using the TV and put it in storage. Now I'm tempted to drag it out of storage and see if I can fix the problem. I managed to find the service manual on google and I found two adjustments "V S CORR" which has a range of 1-15 and "V S CO+" which has a range of -128 ~ +127. Do you think these are the same as SCOR on Sony TVs? Is there a test pattern I could use when adjusting it? thanks for the info.

[rCadeGaming]

I've never worked on a JVC, but it's certainly possible, and if those aren't the values you're looking for the right ones are probably in there somewhere.

Here are some test patterns.  If you have a PS3, you can stick them on a flash drive and display them fullscreen in 480i:







You might be able to do this with a PS2, I forget how it works with pictures on a flash drive, or maybe another console.  The reason I suggest using a PS3 instead of a PC is the PS3's 480i output conforms to NTSC standards, making it a good reference point, whereas as centering and horizontal size with a PC might be all over the place once you've begun using custom resolutions to get it working on a 15kHz display. 

btw, I'm assuming it is a 15kHz display (~240p or 480i only, not 480p or more), so those are 480-line test patterns.  If not, it's not suitable for MAME or old consoles which output 240p (anything pre-Dreamcast).  You could use it for modern gaming though.  I have some 1080-line test patterns if that's the case.

[Calamity]

Also, check this post: http://scarthunter.blogspot.com.es/2013/07/adjusting-vertical-linearity.html