Problems with VGA breakout cable. Need help.

[Popcorrin]

I made a vga breakout cable to hook to my arcade monitor and I am having a couple of issues.  The first problem I am having is that the vertical hold is very very sensitive when I have my monitor hooked to my pc thru the breakout cable but this isn't the case when I hook it up thru a Jpac.  I was curious if anyone would know why it would be much more stable with the jpac?

The second issue I was having is that if I twist the h and v sync together on the breakout cable, to get composite sync, it causing the picture to roll very fast.  The only way I can hook up the breakout cable is by separating the h and v sync going into the monitor.  I was wondering why the jpac works fine outputting composite sync when the breakout cable won't.

[Minwah]

I made a vga breakout cable to hook to my arcade monitor and I am having a couple of issues.  The first problem I am having is that the vertical hold is very very sensitive when I have my monitor hooked to my pc thru the breakout cable but this isn't the case when I hook it up thru a Jpac.  I was curious if anyone would know why it would be much more stable with the jpac?

Did you hook up both H & V syncs of the breakout cable?  I think JPAC's use a composite sync...could have something to do with it.

The second issue I was having is that if I twist the h and v sync together on the breakout cable, to get composite sync, it causing the picture to roll very fast.  The only way I can hook up the breakout cable is by separating the h and v sync going into the monitor.  I was wondering why the jpac works fine outputting composite sync when the breakout cable won't.

Oh, I should've read ahead...

I believe that although twisting H & V syncs is usually sufficient to make a composite sync, some monitors are picky and need a 'proper circuit' to create the comp. sync (rather than just twisting together).  The circuit you can build is the same as for the GunCon2 project I believe...a search of these boards should find it.

[Silver]

Yes Composite sync is not the same as twisting the cables together - it just happens to be enough for lots of monitors.

One of the chips on the Jpac generates a 'proper' composite sync.
As minwah mentions, you can build a simple circuit to convert the syncs correctly.

I presume you are aware about the VGA card on your pc outputting 31Khz or greater (the jpac drops this to 15.75Khz to work with an arcade monitor) - you must be outputting 15Khz directly from the VGA card to get this to work. Based on what you've said you have this partly working anyway.

One other possible option is that your monitor may be able to work with the syncs just twisted together, but you may be kicking out syncs of a polarity that it doesn't like. Syncs generated by a VGA card tend to change polarity based on resolution/refreshrate with no obvious pattern. All PC monitors I've seen don't seem to care at all.

If you are using a Radeon (possible only a newer one) there is an option in the display settings to set the polarity of the syncs. Worth trying different options. the Powerstrip program can also control sync polarity on other cards. I do not know if this will solve your problem though.

[Popcorrin]

I presume you are aware about the VGA card on your pc outputting 31Khz or greater (the jpac drops this to 15.75Khz to work with an arcade monitor) - you must be outputting 15Khz directly from the VGA card to get this to work. Based on what you've said you have this partly working anyway.

I am actually using dos with advmame.  I have advmame configured for my arcade monitor.

One other possible option is that your monitor may be able to work with the syncs just twisted together, but you may be kicking out syncs of a polarity that it doesn't like. Syncs generated by a VGA card tend to change polarity based on resolution/refreshrate with no obvious pattern. All PC monitors I've seen don't seem to care at all.

That's interesting.  Seems possible that this could create problems. 
The main thing that frustrates me though is the sensitive vertical hold.  I can't figure out why it is so much more stable with the jpac.  Does the jpac amplify the sync signals along with the RGB signals?

[Silver]

Ah if you are using advmame, then the syncs are less likely to be the problem - as I think advmame has total hardware control of the output signal being generated....

If the vhold is more sensitive, then either the jpac is buffering the output vga signal to stick to a certain vertical sync over a range of vertical syncs from the card, or as you mention it could be down to voltage differences.

My understanding of how the jpac works suggests to me that its not changing the voltage levels much, but I could be wrong.

I suggest emailing Andy Warne (Ultimarc) for advice, he would be more knowlegable...

[RayB]

One of the chips on the Jpac generates a 'proper' composite sync.
As minwah mentions, you can build a simple circuit to convert the syncs correctly.

Silver you make it sound like a JPAC will take bad PC output and convert it to correct resolutions and everything. That's not correct... My understanding of the JPAC is that it does the following:

1. BLOCKS signals that are out of range (to prevent damage to monitor)

2. Converts 31khz signals to 15khz, but what you see on your monitor will be a "doubled up" image. (2 squished versions of the same image). So just to correct what you said, it will generate a corret signal, but it won't show a proper image. You need either an ArcadeVGA for that, or properly configured tweaked video modes (through PowerStrip or AdvanceMame)

3. It also amplifies the video signal, since many older monitors need a strong signal.

[Scott84]

RayB,

If i bought an arcade VGA and a JPAC, would the onboard video amplifier help the image at all? And isnt it easier to hook it up this way instead of the VGA breakout cable?

It might not be economically viable, but its an easier way for a newb to hook up a monitor right?

[Popcorrin]

Yes it is much easier to hook up a jpac, especially if your cabinet is jamma.

[mamerocks87]

How would it be easier? What all do you have to do to hook up a jpac to the monitor? If anyone gots any pics of this,i would like to see. Thanks,

-Kyle

[mamerocks87]

Okay, see if i got this right. In order to connect a jpac to a arcade montior you need a jamma harness like here:

ebay Link

And the jpac fits into the jamma connector, and the video connector that goes to you monitor is already set up, so you just plug the jamma video connector into your monitor? Is it that easy?

-Kyle

[Scott84]

That jamma cable is so cheap and has quick disconnects already and labels...

can it be good quality too?

[Popcorrin]

Okay, see if i got this right. In order to connect a jpac to a arcade montior you need a jamma harness like here:

ebay Link

And the jpac fits into the jamma connector, and the video connector that goes to you monitor is already set up, so you just plug the jamma video connector into your monitor? Is it that easy?

-Kyle

That's pretty much it.  Don't forget that you have to set up your computer to output frequencies that your monitor can handle.