Help using ultimarc video amp on arcade monitor (with mame)

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Classicgamer
Posts: 873
Joined: Thu Sep 11, 2014 3:37 pm

Help using ultimarc video amp on arcade monitor (with mame)

Post by Classicgamer »

Hi

I am having a problem with a rolling image every time I change resolutions (in mame) when using my ultimarc video amp (with an arcade vga card). I was hoping to get a little advice from people who know about using mame PC's with arcade monitors.

I have a Billabs BL25C90T which is an auto-switching analogue tri-sync CRT monitor. It works in CGA, EGA or VGA and has a dot pitch of approx .8mm. I believe it is the same as the Neiman 24.8" tri-sync flat CRT. It has a 15 pin D-sub and a 6 pin molex connector. The latter requires a higher voltage signal to work at all while the D-sub port works with a 1 volt PC graphics card signal.

My problem is with using the 6 pin molex connection. When using the 15 pin D-sub port, the monitor accepts CGA, EGA and VGA signals and It never loses sync as long as the signal is in that range. When I use the 6 pin molex (with the video amp), the image rolls every time I change resolution (even if both are in the CGA range).

The thing is, when I use the 6 pin connector with the video amp, cga games looks brighter and more "arcade-like". I think that the extra brightness and contrast makes the monitor bloom more which softens the image and smooths any jagged edges. Colors look more accurate too. When I use a 1 volt signal through the D-sub, the image looks a little too clear - i.e. scanlines are thick and black and rounded edges can look a little jagged. It is nowhere near as bad as on my broadcast monitor but it shouldn't be an issue at all on screen with a .8mm dot pitch.

Also, when using mame with a 1 volt signal, the brightness and contrast settings need to be at near max for some games. When I connect my PS3 or I use the 6 pin connection at 5v, the monitor is plenty bright enough at 50% of it's max or less. The monitor is brand new btw.

Adjusting the v-hold to stabilize the image every time I change games is too annoying to live with. It doesn't have this problem when using the 15 pin d-sub port -the image is always stable at any resolution the monitor supports.

Other than the voltage, the other difference between the 2 connections is that I use separate sync with the 15 pin d-sub while the video amp combines the sync from the arcade vga. The amp doesn't use a sync combiner circuit, it just joins the h-sync and v-sync wires together. Could a "dirty" sync signal cause the monitor to roll when I switch resolutions? Previously, when I had sync problems, I got no image at all, not a rolling image that can be stabilized with the v-hold pot.

The monitor has a 75 ohm / 1kohm switch. I normally leave it on 75ohm when using my arcade vga through the D-sub. Does adding a video amp and using the 6 pin molex mean I should change it to 1kohm as if it were an arcade pcb or is this unrelated? Could this cause an unstable image if this setting was wrong?

I wanted to try the video amp with the 15 pin d-sub connection. Will this damage the monitor because the D-sub port is meant for a 1 volt signal? The instructions don't specifically state that the 15 pin d-sub is only for 1 volt signals only, it just lists 2 different specs for "analogue" and "TTL". I know some vga arcade boards use a 15 pin D-sub connection but I'm not sure if they output a 5 volt signal like CGA Jamma PCBs or 1 volt like PC graphics cards.

btw, I know that Mame has it's own settings to increase brightness and contrast but it doesn't look the same as a real 5 volt signal on my monitor. I know it sounds picky but since I saw how good cga games looked with the video amp, I really wanted to find a way to make it work. The video amp is meant for use with an AVGA and arcade monitor so I assume I am doing something wrong unless a rolling image is just an inherent problem with the video amp. As I haven't read about this issue anywhere, user error on my part seems most likely.

I would really appreciate any advice on this.
leonk
Posts: 1080
Joined: Sun Mar 13, 2011 9:29 pm
Location: Toronto, Canada

Re: Help using ultimarc video amp on arcade monitor (with ma

Post by leonk »

Interesting dilemma. because you put it into a cab why did you decide to go with a simple video amp rather than the more commonly used JPAC which has amp, full controls and vga cable input?

The moles connector is designed for real arcade usage. Where resolutions never change. Typically operators either tie hv together in the Miley or leave v offand monitor uses h.

You made the very common but for most monitors false assumption that an arcade monitor should sync to any freq it's fed. This is wrong. Only pc monitors can do that. Operators play with v hold every time they change pcbs

A common solution to your problem is to fix the frequency. That is why old hacks like mamecab or the much newer groovymame exist. Regular mame can't do what you want.

Read the groovyMame forum on byoac forum for more info.
Classicgamer
Posts: 873
Joined: Thu Sep 11, 2014 3:37 pm

Re: Help using ultimarc video amp on arcade monitor (with ma

Post by Classicgamer »

Thanks for the reply. I seem to have found a solution yesterday. I cut the part of the circuit that joins the H and V sync together on the video amp so I could use seperate sync on the monitor. While the monitor is meant to be able to handle composite sync, it doesn't like signal that results from just combining the H and V sync from an arcade vga card.

I think that the info on the Ultimarc site about being able to just join the H and V sync wires together is just wrong. Or at least the resulting sync signal is not clean enough for any of the 3 monitors I have.

Using the molex connectors with seperate sync gives a stable image without needing to adjust the pots when switching resolutions. It can only be used for CGA and EGA though.

On a different note, the image on the monitor with the video amp connected, looks much more like the real Jamma pcb. It's brighter obviously but the image is smoother too as jaggies are less visible. The scanlines are not overly defined now either.

I have read some posts where people talk about getting an image that is "too clear" or one with overly thick scanlines when using a multi-sync arcade monitor. I think that there is a good chance that they are experiencing that issue because they are using a 1 volt vga signal through the 15 pin d-sub input. They don't see the issue on CGA only monitors because they don't have D-sub ports and some don't work as all without a 5volt signal. My tri-sync uses an "A" tube with a .8mm pitch, just like you find on a CGA monitor. Unless the Tri-sync uses an "M" tube like on pc monitors (which a few do), I can't think of another reason for the difference in image clarity.

The colors and contrast look more accurate with the amplified signal too. Whites have a slight yellow tint to them at 1 volt but they turn pure white at 5 v. I thought the color shift was a mame problem before seeing this.
leonk
Posts: 1080
Joined: Sun Mar 13, 2011 9:29 pm
Location: Toronto, Canada

Re: Help using ultimarc video amp on arcade monitor (with ma

Post by leonk »

I'm surprised you ran into issues with sync. Must be monitor specific. For your old CGA only monitors (eg old WG K7000) it works well with both sync tied. That's how most operated it. The only time you had to split it is if you wanted to use a light gun. Light guns don't like combined sync.
Classicgamer
Posts: 873
Joined: Thu Sep 11, 2014 3:37 pm

Re: Help using ultimarc video amp on arcade monitor (with ma

Post by Classicgamer »

I don't think the problem is specific to my monitor. I think it is an arcade vga problem. I have had 2 different arcade vga cards and had problems getting composite sync from both of them on 3 different monitors. I have my arcade monitor, a Sony trinitron tv and an Ikegami 20" broadcast monitor.

The arcade monitor is the only one that works with both composite and seperate sync. Twisting the H and V sync wires together from the arcade vga doesn't work at all on the Sony tv or the Ikegami monitor without a decent sync cleaner and combiner. I bought my extron RGB interface because I needed a device to create a clean composite sync from the arcade vga. Before that, I tried using a jrok sync cleaner which half worked but the resulting image quality was terrible.

Twisting the sync wires together when using my arcade monitor only seems to work if I adjust the H and V hold every time I change games which is too time consuming to live with. When I used the composite sync from my extron rgb interface, I don't have that issue on the same arcade monitor.

My guess is that twisting the 2 wires together from the arcade vga just gives you the horizontal sync, not composite sync which is why my monitor can't hold sync on it's own without constant adjustments to the v hold.

People using jamma pcb's might not notice an issue at all because they adjust the v hold once to make one game work and then they leave it like that. Also, a number of arcade monitors can accept seperate sync anyway. It is also probable that arcade boards put out real composite sync.

Using an rgb interface is not a big issue as they are cheap. The problem for me is that they don't output 5v on pin 9 to power my video amp so i would need to find a seperate stable 5v source. Apparently you can't use a mains adapter because they don't provide stable voltage.

For anyone not using a video amp with their arcade vga card, I strongly suggest using an rgb interface to get composite sync instead of twisting the sync wires together. It makes life a lot easier when using rgb monitors that require clean sync.
pacboy
Posts: 1
Joined: Fri Mar 15, 2019 1:44 pm

Re: Help using ultimarc video amp on arcade monitor (with ma

Post by pacboy »

Sorry to revive an old post, but I have this same monitor and I was wondering if you figured out a way to use it with VGA resolutions too? Since you can't use the molex connector for VGA, I'm thinking that you could plug the VGA cable coming out of the graphics card into a switchbox, then run 2 cables out of that, one going to the molex (using the amp) and one going to the d-sub input?
Did you ever attempt to boost the d-sub signal? I agree that sounds like it could do some damage.

Thanks
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