Software Support > GroovyMAME
Artifacting on Nanao MS8 29FSG w/ CRT Emu Driver (SOLVED!)
BumbleChump:
--- Quote from: Zebidee on March 09, 2020, 07:06:36 am ---Try isolating/bypassing your JAMMA completely and feeding video signals directly into the monitor. Signal should be weak but visible - see if you still get artifacting. If the artifacting disappears, then it looks like your JAMMA or maybe the jpac is the source of your problems.
You shouldn't be getting any sparks when connecting JAMMA, even when power is connected (this is bad form anyway, you might cause some damage). Video signals are very low voltages. There are 12v & 5v available on JAMMA if you have a DC power supply connected inside your cab, but even then sparks would be unusual and alarming. I suspect that you have some problem with the grounds in your JAMMA connector.
--- End quote ---
Wasn't able to try this yet since I realized I need a way to combine the VGA syncs without using the Jpac. I also confirmed that the video ground and general ground are not connected in the jamma harness. I'm going to try something weird though, inspired by this thread:
http://forum.arcadecontrols.com/index.php/topic,158700.40.html
He was able to solve his problem by having a lowpass filter in the chain, so I'm going to use a PVM in the chain. It has outputs for every input, and I'm hoping it will clean up the signal?
GPU>VGA>JPAC>Super Gun>SCART/BNC>PVM>BNC spliced to Jamma harness
By the way, did you ever make that low pass filter for that guy, Zebidee? Did it work out?
buttersoft:
I don't think using the PVM will do anything. The PVM has passive pasthroughs, the use of which removes the 75R termination required by analog video equipment. The last monitor in the daisy chain has the 75R terminations. Arcade monitors do not often use or require these terminations. The lack of them might make the image on the PVM brighter but ghosted a little.
It's worth a try because everything that's not going to hurt is worth a try, but i'd be surprised if you see any positive change.
Can you not output composite sync from your video card directly using crt_emudriver? If not, a 500R resistor and then 1K pot in each sync line, then combine, should give you working sync. Just dial the pots around.
Zebidee:
A warning note here about arcade monitors and grounds: Be aware that arcade monitors, at least older ones, typically use have a "hot" chassis and require an isolation transformer to physically isolate the chassis from the normal electrical wires. Effectively they have a "local" ground at this point and it *must* be separate from any mains or other grounds. So whatever you do don't ground the chassis to anything else. In summary it can create a situation where you are more likely to be electrocuted, and you may zap something you don't mean to.
Now having said that, your video signals terminate on the "cold" side of the chassis, which means it is OK for your video grounds to be connected all the way through from the chassis to the JAMMA to the PCB/PC etc; and in fact they should be, so this is definitely something to check. You can easily check continuity end-to-end using a cheap multimeter on the diode setting.
--- Quote from: BumbleChump on March 11, 2020, 02:55:04 pm ---Wasn't able to try this yet since I realized I need a way to combine the VGA syncs without using the Jpac.
--- End quote ---
I would never argue with Buttersoft because he is wise and knows his stuff - but I say you'll be fine just twisting the H&V sync wires together for the purposes of using a VGA breakout cable to test the monitor (assuming that your PC outputs negative sync on both H&V - which is the ATI default so it will be unless you've changed it). Arcade monitors expect higher voltages than TVs so no need to pull it down.
However, putting resistors on sync lines when making cables for TVs is prudent as the standard for TV sync is 0-1vpp, whereas for PCs it is 0-5vpp, so pulling the voltage down makes sense (Full disclosure: I've made plenty of VGA-SCART cables with no resistors and used them with lots of TVs, still am using them, have been for years and years, never had any problems, but maybe it's because my TVs are better-quality ones. If I was to make a new cable tomorrow I'd probably try a 680ohm or 1k ohm resistor on the sync, can't hurt).
--- Quote from: BumbleChump on March 11, 2020, 02:55:04 pm ---I'm going to try something weird though, inspired by this thread:
http://forum.arcadecontrols.com/index.php/topic,158700.40.html
He was able to solve his problem by having a lowpass filter in the chain, so I'm going to use a PVM in the chain. It has outputs for every input, and I'm hoping it will clean up the signal?
By the way, did you ever make that low pass filter for that guy, Zebidee? Did it work out?
--- End quote ---
Unfortunately life and injuries got in the way after I posted that and I've been finding it hard to get back to my hobby (or even to get into my shed) for the past year or so. However I did eventually make that little video amp circuit as I was attempting to improve a blooming issue I was having with a cheap Chinese arcade monitor - I was using an Ultimarc video amp and it seemed to be boosting the video signals too much, making the picture "bloom" heaps whenever something bright happened. It worked, but was a bit ugly. Unfortunately something else came up and I never got to make a second one for Sublevel (or even to take that particular arcade cab project much further - it is still on-hold).
Proof:
BumbleChump:
--- Quote from: buttersoft on March 11, 2020, 08:31:29 pm ---Can you not output composite sync from your video card directly using crt_emudriver? If not, a 500R resistor and then 1K pot in each sync line, then combine, should give you working sync. Just dial the pots around.
--- End quote ---
Oh duh, I forgot about that. I can definitely just splice it to the Jamma. Thanks for the reminder. Also I'll wait on the PVM thing. Gonna make a low pass filter instead.
--- Quote from: Zebidee on March 11, 2020, 11:47:10 pm ---Unfortunately life and injuries got in the way after I posted that and I've been finding it hard to get back to my hobby (or even to get into my shed) for the past year or so. However I did eventually make that little video amp circuit as I was attempting to improve a blooming issue I was having with a cheap Chinese arcade monitor - I was using an Ultimarc video amp and it seemed to be boosting the video signals too much, making the picture "bloom" heaps whenever something bright happened. It worked, but was a bit ugly. Unfortunately something else came up and I never got to make a second one for Sublevel (or even to take that particular arcade cab project much further - it is still on-hold).
--- End quote ---
As far as I know, Astro Citys don't have an isolation transformer, and the monitor is not supposed to be grounded with the other metal parts in the cabinet. And that's a bummer on the injuries! Hope it's better now.
I was wondering though, if you use that video amp you made with a Jpac, isn't that amplifying the signal twice?
Zebidee:
--- Quote from: BumbleChump on March 12, 2020, 12:14:59 pm ---As far as I know, Astro Citys don't have an isolation transformer, and the monitor is not supposed to be grounded with the other metal parts in the cabinet. And that's a bummer on the injuries! Hope it's better now.
--- End quote ---
Embarrassingly, I used to own an Astro City with that monitor (loooong time ago). I can't remember whether it has an ISO or not (pretty sure there is one). If there is no ISO, then there would be a bridge rectifier on the chassis power supply that eliminates the strict need for one, although they are still desirable as they make the monitor much safer (much less likely to electrocute yourself). To complicate things, cabs use step-down tranformers to get the right voltage, which may also be an ISO transformer even if they don't technically need an ISO. But for your purposes this doesn't really matter - just don't ground the monitor chassis to anything else (video signal exception).
Thanks for the good wishes - Injuries all better now, I really appreciate walking!
--- Quote ---I was wondering though, if you use that video amp you made with a Jpac, isn't that amplifying the signal twice?
--- End quote ---
I wasn't using a JPAC then - I was running the signal directly from PC to arcade monitor using a VGA breakout cable->amp->monitor. The composite sync was achieved by simply twisting together wires from pins 13&14, no resistors, directly PC-VGA -> monitor. Very stable. The home-made video amp only processes the RGB signals, does nothing with the sync.
On stable csync - I've found csync via CRT_emudriver to be less stable. A possibly related problem with using csync from CRT_emudriver is that if you have pin 14 (vsync) connected it will create interference on sync, so you if you've made cables with pin 14 connected you'll have to undo and disconnect it. After experimenting a few times I decided it wasn't worth the bother. All my cable are made with 13+14 connected so I'll just stick with that unless I have to change for some reason.
People make such a big deal about csync. If you really want to get fussy about csync then you can get some LM1881 chips and make your own sync combining circuit quite cheaply with a few capacitors and resistors, but you really don't have to bother in this case as twisting 13&14 together and putting them into the sync input on your monitor will be all you'll need.
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