[SOLVED] NEC XM29 and Genesis RGB sync issues

[srarcade]

Just got a XM29 and i have been testing my consoles. I first tested the Saturn (RGB modded) and it worked with zero problems and looked fantastic. I then tried the Genesis which is also RGB modded but the monitor will not sync for some reason. I then tested the Genesis on an arcade test monitor (13" Happ shelf monitor) and it looked fine. So for some reason, the NEC XM29 is not happy with the Genesis sync. So for kicks I added a LM1881 sync stripper circuit in line on the composite sync out (which also has a 75ohm + 220uF cap on it) but no dice.

Any ideas here?

Thanks

SOLUTION: On the XM29 there are toggle switches under each input that say 75ohm/HIGH. According to the manual, you are to leave all these at the 75 ohm setting if you are running a single monitor and only set them to HIGH if you are running them to another monitor. Well.. for kicks I set it to HIGH anyway and bingo, my sync worked! Why does it work? I'm not sure, it just does lol

[STG]

Yeah, I've had the same issues with the Genesis (Model 2) and CDX playing nicely with my XM29. My solution was to use an Extron sync processor, both the SC210 or the PA250 worked for me. You can pick up a used one for cheap on eBay.

You can also use these Extron boxes to help stabilize other RGB output (like for arcade games) or use them to separate H and V for a device like the Micomsoft XCapture-1.

[srarcade]

Excellent, thank you - I remember seeing these Extron units awhile back. I'll definitely pick one up cheap. I can see where it would be needed, like on screens where there is a white wash the monitor tweaks out.

[STG]

Excellent, thank you - I remember seeing these Extron units awhile back. I'll definitely pick one up cheap. I can see where it would be needed, like on screens where there is a white wash the monitor tweaks out.

It'll definitely help with those situations! They're especially worth it if you go the supergun route, as I have a few unstable PCB's that would be nice and stable on my BVM but would flicker on the XM29.

Either of those two units fixed every problem I ever had and they're handy to just have on hand, fyi there's a PA300 which "appears" it would do the trick as well but I haven't tested it personally with my setup. Hope that helps!

[srarcade]

I picked up a Extron PA250 for $10 and it works nicely. Definitely a great boost of signal for those weaker sources! Thanks again for this recommendation.

I'm still having one problem on my XM29 that is preventing me from really using it and that is it appears to be having signal "overload" on wash screens with white or pure white areas on a screen. The screen will lose picture (inverting to black and scrambled picture) and then the crt will actually cut off (you can hear the relay click) and then back on when the screen changes to something else it can understand. Any ideas? I tried playing with the dip switches and other items on it, no luck.

[STG]

How strange. I had the same issue years ago with my Megaview losing sync on a white (or nearly white) screen, and oddly enough, it would only do it with the SNES in my case. For example, using a bomb in Contra III would set it off immediately.

The monitor ended up dying and I ended up getting a different RGB cable for that system over the years, but honestly I don't know if that might be the solution to that particular problem. It's never happened with my XM29. Out of curiosity, does lowering the level on the front of the PA250 help?

Edit: Also, are you running your consoles through any other device besides the Extron unit, like a switch for example? And does it only happen on one console or all of them?

[srarcade]

I have jamma modded all my consoles so that's how they connect. Last night I was testing with a NeoGeo MV2F but the Genesis was doing it as well. I built a supergun so the jamma harness goes into the box, then goes through a Sega filter/clamping board (the kind you find on th e big rear projection games) that converts to BNC output, from there it goes to PA250 and then to the XM29. I can try to remove the Sega board next, perhaps that's introducing the issue.

If i turn the PA250 all the way down, it still happens.

[STG]

That's an interesting way to convert the signal to BNC. I'd be curious to hear if removing that Sega board will do the trick!

[srarcade]

Fixed! I also had an Ultimarc RGB amp in my super gun for weaker sources which is selectable by switch but ultimately feeds the same outputs. Apparently there was some feedback coming from that even with the signal bypassing it causing it to overdrive the image. Removing the amp fixed that immediately. I'll have to put some diodes on the lines or something to maybe keep that from happening. I may not even need that amp now with the PA250 box.

[robneal81]

I picked up a Extron PA250 for $10 and it works nicely. Definitely a great boost of signal for those weaker sources! Thanks again for this recommendation.

Does the Extron SC210 act as a sync stripper, in situations where you're using composite video as sync? I have to use a Sync Strike with my XM29, otherwise it won't work, but I'd rather switch to the PA250 (for a long, boring reason I won't waste your time with). I just need to confirm that it acts as a "sync stripper" and converts composite video to csync.

Thanks for your help.

[ELabit]

Sorry to necrobump but this also solved my problem tonight. I've used my XM29 with all my consoles and never have an issue. I put a LM1881 in my scart to BNC cable and everything syncs. I built a scart cable for my MSX 2 recently but couldn't get it to sync. It worked on my other PVMs just fine. I tried it with straight composite sync, no dice. Also tried through the LM1881 but still nothing. Flipped that 75ohm switch to high and that solved the issue. Thanks to TheSteve for some advice as well and pointing me to this thread.

[lalilulelo]

Sorry to revive a long dead thread, but I had something to add to this. I have an XV29 Plus, and it has a problem that seems like it might be related to what's being described here. With my monitor, the image becomes dark and distorted at seemingly random times. I had the idea that this could have something to do with slight fluctuations in the sync signal, which maybe the monitor isn't able to handle for some reason. The XV29 doesn't have the "75Ohm" switches that other people described here, at least not on the outside. I have looked inside the monitor, but I wasn't looking for that specifically, so I'm not sure if there are switches there or not.

Anyway, I did notice something early on with the monitor, which is that this issue seemed more likely to happen after I tried to use the monitor with a sync signal that it couldn't handle. Since then it happens at seemingly random intervals. It's hard to say for sure why the problem happens, but the idea I had was that the monitor somehow has difficulty regulating the level of the sync signal - so maybe a device like the PA250 could help stabilize the sync signal and thus solve my problem. I do have a SCART to VGA adapter with an LM1881 inside that I built, and I've been doing some testing of that lately - but so far I can't say anything conclusive about the effect of the LM1881, other than that it successfully converts composite video or luma to composite sync. One odd thing I noticed while testing was that when I'm using my PS2 with the LM1881, for some reason when I go to the signal information in the menu - it lists 15.7kHz as the H rate, which is normal, but for the V rate it says 535.0Hz. I haven't checked the signal of all of my systems, but I know that with most other systems it gives reasonable numbers for the V rate. The monitor obviously isn't running at 535Hz, but I wonder why it says that. It seems like it may actually be somewhat more stable with the LM1881, but I need to do more testing to confirm that.

It's possible that the monitor has permanent damage now, but it seems like there's at least a chance an Extron device might help. Thoughts? Does what I'm saying seem reasonable?

I'd also like to know if anyone has an answer to the previous poster's question: can the PA250 or SC210 work as a sync stripper? I looked at the specifications, and it looks like the answer is yes, but it'd be helpful if someone could confirm that.

[BuckoA51]

Wouldn't this actually make sense to set it to high since if you use an LM1881 doesn't that output TTL sync rather than 75ohm?

Anyway I'm not sure it's much help but adding an Extron interface to my Mitsubishi Megaview (which I'm told is very similar) actually caused problems with my Genesis, rather than solving anything.

I leave mine on high since I feed it from an Extron Crosspoint.

[rama]

I've had various issues with Mega Drive sync over the years. One Sony consumer TV had the dark picture problem.
The issue seems to be with how CSync is handled within the console.

If you look at the waveform as it arrives at the TV / upscaler, it looks pretty bad already.
Additionally, the console has that 256px setting that some games use, which widens the horizontal sync pulse, possibly too far out of spec for NTSC.
If the TV / upscaler attempts to clamp the RGB channels based on such a malformed sync, it can start clamping active video, causing the dark colors.

I haven't tried this yet, but there's this 2.2kOhm pullup resistor for CSync in the console.
This could be a bit weak (especially if using CSync directly from the AV port).

[lalilulelo]

Wouldn't this actually make sense to set it to high since if you use an LM1881 doesn't that output TTL sync rather than 75ohm?

Like I said, the XV29 Plus doesn’t have that switch - unless it’s inside, but if so it’s probably in a place that’s difficult to reach.

Anyway I'm not sure it's much help but adding an Extron interface to my Mitsubishi Megaview (which I'm told is very similar) actually caused problems with my Genesis, rather than solving anything.

What problems did you have with the Genesis when you were using the Extron interface?

I've had various issues with Mega Drive sync over the years. One Sony consumer TV had the dark picture problem.
The issue seems to be with how CSync is handled within the console.

The problem I’m having seems to affect all of my systems, not just the Genesis. That said, whenever the problem doesn’t happen, they all work just fine. The idea I had is that almost every console has some slight irregularities that a TV or monitor would normally be able to compensate for, but for some reason my monitor can’t.

If you look at the waveform as it arrives at the TV / upscaler, it looks pretty bad already.
Additionally, the console has that 256px setting that some games use, which widens the horizontal sync pulse, possibly too far out of spec for NTSC.
If the TV / upscaler attempts to clamp the RGB channels based on such a malformed sync, it can start clamping active video, causing the dark colors.

You could be right about the monitor clamping the video. I had an issue with a scaler (a GBS-8220) which turned out to be related to the clamp setting, and now that I think about it, the visual problem it had was kind of similar to the problem with my monitor.

Another thing: I've been talking to this person about getting a VGA switch, and they just sent me a picture of this thing called a "video distribution amplifier". It appears to be a powered VGA splitter of some kind. I noticed that it has switches for RGB and sync labeled "75" and "High". I wonder if this could be useful to me, since my monitor doesn't have those switches. It's a Vidco VDA300.

[rama]

Yeah, that's a TV issue.

Maybe the set requires a different configuration.
Not sure if you've found a service manual yet, but here's a start:
https://www.manualslib.com/manual/10986 ... =12#manual

There might even be a clamp position control in there somewhere.

[lalilulelo]

I've looked through the manual quite a bit, and I've searched the menus for anything that could make a difference - nothing seemed to help. I don't know of a clamp setting anywhere in the menus, and it isn't controlled by the dipswitches. It's possible it could be in a hidden menu or something. Do the XM29 or XM37 have a hidden menu? The menus that I am able to access are somewhat limited.

Another issue: adjusting the clamp could cause issues, because there doesn't appear to be a way to reset the monitor's settings without the menus - so if I mess it up and I'm no longer able to see the menu, there would be no way to change it. There could be something inside the monitor that allows you to do a full reset, but I don't know where it would be. Anyway, I think I would need to have some idea of what the normal setting for this would be, which I don't.

[lalilulelo]

So, I've done some more testing with the LM1881. I tested it for about a week, and it seemed be working well, but just today the problem came back. I noticed something interesting, though - when the problem happened this time, I noticed distortion (bending) of the image in the middle, which I never saw before. This almost certainly has something to do with the sync, though I'm not sure if it's directly related to the other problem. I'm not sure why the problem came back with the LM1881, but it could be that I didn't do a good job when I was building the adapter I use with the LM1881 - and as a result of that, the sync isn't stable enough. I'm still inclined to get the PA250, though I haven't decided for sure. It seems like, if nothing else, it could be useful for diagnosing the problem.

Here's a photo of the distribution amplifier I mentioned before.



I know of a way to eliminate the problem when it happens (temporarily), and one question I haven't been able to answer is why that works. The solution I've found is to connect and/or disconnect a cable to/from any of the inputs - and it seems to work the most reliably if I use a single RCA connector connected to the composite input on the back. I can't explain why this eliminates the issue, but it seems like maybe there's some kind of feedback loop and connecting an input breaks the loop. Another possible explanation is that a component inside the monitor which is supposed to regulate the voltage of the inputs sometimes fails, and connecting/disconnecting a cable causes it to be reset to its default value. I've wondered if there might be a way to utilize this phenomenon to permanently fix the problem, but I don't know how I would do that.