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Atomiswave jamma to rgb modded JVC issue

santeegmc

santeegmc

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Hi Everybody,

Having an issue when connecting my Atomiswave to a JVC TV that I have rgb mux modded.
After some trial and error I managed to get things running by using the vga port on the Atomiswave, splicing into the rgb, ground and sync and hooking that into the new rgb lines for my TV. I have the sync connected to the composite video input of the TV.
My original plan was to use the jamma connection, but when hooked up through the jamma the tv will suddenly cut off and blink the power light. This always occurs when turning on the Atomiswave during the logo screen. I can wait to hit the rgb switch and get it to function after the title screen but then it will cut out again right before the level starts. The game is sports shooting usa, not that the game choice really matters.
The rgbs have inline resistors as well as the sync. Sync is running around 1.4v after resistors and does not fluctuate during power up or game play.
I'd like to get it to run with the jamma so I can eventually put multiple light gun arcade boards in a cab and use a jamma switcher to hook them all up.
Is this a problem that anyone has come across? I'm thinking it has something to do with the sync or maybe the ground is sending a signal that the JVC doesn't like? Its got me puzzled, especially do to the fact it works just fine using vga out. I've posted this on the
Shmups forum, not much feedback, figured here may be a better fit.

Any advice is appreciated
Thanks.
 
Sounds like you know way more about modding than I do
I'm assuming the JVC is 240p/480i only?

Just wondering why you didn't go the route of using a Supergun?
You get RGB out and if your TV has component inputs use an RGB2COMP Transcoder and your good

For the Cab stuff just use a second Atomiswave MOBO they're pretty affordable :D
 
What resistor value do you have on the sync line? Not sure what is needed with the mux mod, but 1.4v sounds too high. You could use a simple voltage divider to half that output, or adjust the current value to reach the correct level…
 
Complete noob to the rgb modding world, but there was enough info out there to help me get this far. My TV has composite/ svideo only, so not sure a Supergun will help. I could get one and hook to the new rgb lines, but figured I really shouldn't have to.
I used 510 ohm with 180 ohm on the ground. This combo is what the rgb lines have as well. Sync shows like 4.4v before the resisters. I think ideally it should be below 1v so I might try some different combos.
Any idea why it would work fine with the VGA output? I didn't try getting a voltage reading from the VGA, suppose that info could help.

This is the mux mod link I followed.
https://shmups.system11.org/viewtopic.php?t=69727
 
Check your voltage maths here:
Voltage Divider Calculator
Believe vga sync should be 5v, so perhaps shift out the 510ohm for 1.2k instead…
Sync should be 0.7v or possibly lower… I forget.
 
I did some voltage checks.
Before any mods, coming from the Atomiswave, Vga seems to be putting out way lower volts on the rgb compared to the jamma. Like .5v vs 5v. The sync is high on both, like 4.4v. So sync may not be the issue.
Now I'm thinking when using jamma the rgb's are spiking at certain points making the tv turn off.
The resistor values from the mod are probably not enough. I don't really feel like redoing all that. So I'll try to put some inline before they hook up to the tv.
Any reason this is a bad idea?

Thank you to everyone for the help.
 
RGB should be 0.5v for VGA, so doesn’t sound like it should be a problem… Sync is TTL level and needs to be attenuated for sure. How are you measuring the levels wrt spiking?
 
I have a multimeter hooked up while it's running and watch the voltage. Probably not the best method but it gives me some readings. On the rgb I can see the voltage go up to 5v occasionally.
I got the sync down to 1.1v. Is that too high? Works fine when using the vga.

I added some more resistors to the rgb lines from the jamma, got those much lower, they'll fluctuate during game play but from what I can tell it's around 1v now. I think this solved the issue, but if I need to go lower I will.
Is going lower on the voltages better for the TV?
 
Consumer level signals (like RGB from consoles) with 75ohm impedance should ideally be 0.7v.

Jamma uses 1000ohm impedance which is around 5v.

The issue is while VGA is 0.7v for RGB it's still 5v for sync. You need to drop sync to 75ohm levels since you're sending it into composite video.
 
You should really buffer the Jamma edge RGB lines due to the impedance mismatch as mentioned by @notsonic.
The issue was the TV turning off on the Atomiswave logo? Which is almost all white?
 
Yep, the plan is to get them down to .7v.
Yes the first power up screen is very bright and mostly white.
I read that someone put potentiometers on the rgb lines to make them adjustable. I think I might go that route as well. I'll probably want to make adjustments when I start adding other games. The pots will surely come in handy.
 
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