Sega Model 3 resolution

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lalilulelo
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Sega Model 3 resolution

Post by lalilulelo » September 23rd, 2018, 6:16 am

So, I have a Model 3 system (Virtua Fighter 3) which I've had for years. It's fully working, and I'm able to play it on a VGA monitor using a GBS 8220. However, a goal of mine from the beginning was to be able to display the Model 3's output natively on a CRT, without scaling. My intention was to get a monitor that supports 24kHz medium-res, but just recently I've been thinking about something. A user on another game forum told me a while back that there's actually a way to get a Model 3 to output 640x480. The user said that there's a jumper somewhere on the board that you switch, which changes the resolution. Unfortunately, he didn't know which one. The Model 3 does have multiple jumpers, but I'm not just going to randomly switch them, because it could cause problems, and also because switching some of them would require fully disassembling the boards - which is a pain in the **** for multiple reasons.

Something else that got me thinking about this is this video I saw on YouTube a while back:


It's a promo video for Virtua Fighter 3. In that video, it lists the resolution as "496x384~640x480". Apparently this video was shown in 1996, which was after the first Model 3 systems were manufactured (mine was manufactured in '95) - so I would think that the specs listed here are final. I guess it's possible that it means that the system internally renders the image as VGA and then downscales it to medium-res. I don't know. Apart from that video, I can't find any other information about this on the internet. I did find the manual for Virtua Fighter 3, which has a schematic of the board, but the resolution is rather low so I can't get much information from that.

So, I wanted to know if anyone has any ideas about this. Is there any way to get the Model 3 to output 640x480? Any help would be appreciated.

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Re: Sega Model 3 resolution

Post by Layer » September 23rd, 2018, 7:22 am

Sega Model 3 system resolution is indeed 496 x 384 (one or two plane 24 kHz), so you need a multisync monitor that supports 24 kHz frequency.

You can use a CGA/EGA to VGA converter to output in 640 x 480 resolution, but I don't recommend Gonbes GBS scalers as they are unstable with hybrid frequencies.

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Re: Sega Model 3 resolution

Post by lalilulelo » September 23rd, 2018, 7:36 am

Layer wrote:
September 23rd, 2018, 7:22 am
Sega Model 3 system resolution is indeed 496 x 384 (one or two plane 24 kHz), so you need a multisync monitor that supports 24 kHz frequency.

You can use a CGA/EGA to VGA converter to output in 640 x 480 resolution, but I don't recommend Gonbes GBS scalers as they are unstable with hybrid frequencies.
That's what I thought, but why do you think this video mentions 640x480? The Model 3 works fine with the GBS 8220.

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Re: Sega Model 3 resolution

Post by Layer » September 23rd, 2018, 7:45 am

It may be due to the fact Model 3 system has an hybrid resolution varying a bit.

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Re: Sega Model 3 resolution

Post by copados33 » September 23rd, 2018, 7:55 am

I use an Asus VS247 27" LCD panel for all my model 3 stuff.

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Re: Sega Model 3 resolution

Post by Layer » September 23rd, 2018, 8:03 am

AFAIK VS247 model is 24".

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Re: Sega Model 3 resolution

Post by lalilulelo » September 23rd, 2018, 8:14 am

Layer wrote:
September 23rd, 2018, 7:45 am
It may be due to the fact Model 3 system has an hybrid resolution varying a bit.
I didn't know about that, but I thought Model 3 cabs don't support 31kHz. I've tested the scan rate and it seems to stay at 24kHz, though I guess it's possible that it changes in another part of the game.

copados33 wrote:
September 23rd, 2018, 7:55 am
I use an Asus VS247 27" LCD panel for all my model 3 stuff.
I specifically want to use a CRT. There are several options, it's just that they're hard to find and expensive. By the way, I have a 27" ASUS monitor (PB278Q), but as far as I know it doesn't support anything below VGA.

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Re: Sega Model 3 resolution

Post by DaveyD » September 23rd, 2018, 12:33 pm

It might be that on a technical basis the model 3 can do 640x480, but no games were written to function at that resolution.

When you look at the spec for the taito Gnet it says up to 740x480, but all the games are in standard cga resolution

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Re: Sega Model 3 resolution

Post by cools » September 23rd, 2018, 1:22 pm

Gnet does 480i
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Re: Sega Model 3 resolution

Post by leonardoliveira » September 23rd, 2018, 3:38 pm

There's a pair of jumpers on the MODEL3 board which swaps around the clock source for the video chipset. You can toggle between 24Khz and 31Khz by changing them.

It also can do SoG (Sync on Green) by toggling a jumper on the third (video) board.
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Re: Sega Model 3 resolution

Post by lalilulelo » September 24th, 2018, 4:58 am

leonardoliveira wrote:
September 23rd, 2018, 3:38 MP
There's a pair of jumpers on the MODEL3 board which swaps around the clock source for the video chipset. You can toggle between 24Khz and 31Khz by changing them.

It also can do SoG (Sync on Green) by toggling a jumper on the third (video) board.
So does that actually change the output resolution? I mean, change it to output 31kHz rather than 24kHz. Which 2 jumpers?

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Re: Sega Model 3 resolution

Post by leonardoliveira » September 24th, 2018, 5:18 pm

If you look around the corner of the cpu board there's 24Mhz and 31Mhz crystals near each other with blue jumpers near them. Change all to the other side.

Marked on the red square.
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Re: Sega Model 3 resolution

Post by pulstar » September 24th, 2018, 5:49 pm

Wow. Never knew Model 3 PCBs could output 31khz. I'm going to give that a go on the weekend with my VF3 stack. Thanks for the info :D

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Re: Sega Model 3 resolution

Post by nem » September 24th, 2018, 6:37 pm

I just tried this with Fighting Vipers 2. I couldn't get either a MS-2930 or a 2931 to lock on to the image after swapping over the jumpers. It's just a squiggly mess.

Also, the crystal on my board is 32Mhz.

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Re: Sega Model 3 resolution

Post by lalilulelo » September 25th, 2018, 1:35 am

leonardoliveira wrote:
September 24th, 2018, 5:18 MP
If you look around the corner of the cpu board there's 24Mhz and 31Mhz crystals near each other with blue jumpers near them. Change all to the other side.

Marked on the red square.
Cool, thanks for the info! I'll try this out soon. Apparently this doesn't even require disassembling the boards, so it should be really easy to do. My setup is a little messy currently, so it'll probably be at least a few days until I can try it out. Also, the crystal says "V-32M000". I wonder if that means 32kHz, like nem said. My monitor seems to accept resolutions that are just slightly above 31kHz though, so maybe it'll work. I'm also not sure if it will accept composite sync, but I guess I'll find out.

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Re: Sega Model 3 resolution

Post by lalilulelo » September 25th, 2018, 8:14 am

Update: so, I switched the jumpers, and I can't get it to work so far. My monitor gives me an "out of range" error or something like that. It also lists the sync as: "18.7kHz horizontal, 44.1Hz vertical", which makes no sense. With the jumpers in their default positions it lists it as something like ~24kHz horizontal and ~59Hz vertical, which makes sense. So, switching the jumpers seems to be changing the scan rate, but not to 31kHz. It's possible that my monitor just doesn't accept composite sync, but that doesn't explain why it lists the scan rates correctly when the jumpers are in the default position. I also tried connecting it to the GBS 8220 with the jumpers switched, just to see what would happen, and it said "No Signal". Normally it works fine.

One idea I have is that 18.7kHz H and 44.1Hz V are kind of close-ish to .75 times their normal values. I'm not sure what to make of that, but maybe each jumper actually does something different, and the combination of all 3 together leads to it being .75 times the normal value. I thought the jumpers were only supposed to change the H scan rate, so why is the V scan rate also changing? Of course, it's possible my monitor is showing incorrect values.

Any ideas about what's going on here?

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Re: Sega Model 3 resolution

Post by leonardoliveira » September 26th, 2018, 12:21 am

There might be other jumpers to change. I remember making VF3 work on some generic VGA monitor way back then. 10+ years ago. I don't really remember exactly what I did.

Check the video board for more jumpers. Just make sure you document their original positions before changing.
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Re: Sega Model 3 resolution

Post by lalilulelo » September 26th, 2018, 5:40 am

leonardoliveira wrote:
September 26th, 2018, 12:21 am
There might be other jumpers to change. I remember making VF3 work on some generic VGA monitor way back then. 10+ years ago. I don't really remember exactly what I did.

Check the video board for more jumpers. Just make sure you document their original positions before changing.
I tried many of the jumpers on the CPU board, to no success. I'm not sure that I want to mess around with the video board unless I know exactly what to do. If there's more than one jumper, which I assume there is, then that means I have to completely disassemble and reassemble the system for each one. Plus, my boards seem to have connection problems when you initially assemble them, so I'd have to mess around with that to get it working, again, every single time. It's too bad there's no available documentation on what each of the jumpers do. Do you remember how you found out about this originally? Did you read it somewhere, or was it in a manual or something?

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Re: Sega Model 3 resolution

Post by leonardoliveira » September 26th, 2018, 2:28 pm

I only had the board set and the filter board, I wanted to try playing it really bad and I had no 24Khz capable display so I just took notes of the board jumper positions (at the time I only had film cameras so making pictures was not practical) and experimented with the jumpers. I even discovered that the video board has a jumper to enable SoG at the because when I enabled the said jumper the display became "green-ish"... I no longer have said notes, of course considering that was 10+ years ago, I've moved twice since then.

Since green receives H/V sync too when SoG is active, the green voltage becomes different and if the monitor isn't aware of the sync signal on green it will make the image look more green than it should be...
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Re: Sega Model 3 resolution

Post by lalilulelo » September 28th, 2018, 8:31 am

I guess I'll have to do that myself at some point. Not sure when. My guess is that, if you're correct in thinking that there's another jumper that needs to be switched, it's probably on the video board - because I've already tried almost all of the jumpers on the CPU board. Although, I just noticed that there's another crystal on the CPU board that I think says "TNC-2 OSC 33.000MHz T.Q.C." with 4 jumpers next to it. I wonder what that is. Anyway, before I even attempt to do anything else I really need to solve a problem I'm having with the PSU. I should probably make another thread about that.

One thing I was wondering about: when you managed to switch the resolution, did it actually change the resolution the game was rendered at, or did it just upscale it to 640x480 or something like that? If it's the former, that would be pretty awesome.

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