NEC XM29 Monitor Issue [RESOLVED]

[Omegaknuckles]

Disclaimer: Buckle in. My posts tend to be long.

I've recently obtained an NEC XM29 (standard model) monitor for my so-called WIP "game room". I picked it up for free, as-is from a person down in Champaign, IL. I let them know I would most likely be able to troubleshoot and remedy the problem (at least according to the legally recognized pieces of paper that say I'm qualified to do so).

So, here I am at the first stage of fixing this monitor, diagnosis.
I turn it on and the monitor tunes to the input as properly as an XM29 can be expected to (no saveable raster adjustments to my knowledge), and I end up with images that look like this (minus any inevitable moire from my Fujifilm camera lens):

http://puu.sh/k45X1/1c2a2a93ef.JPG

http://puu.sh/k3YTL/113ecbe9a8.JPG

http://puu.sh/k3YVz/6fc319a76d.JPG



The monitor appears to be experiencing an issue I have no prior knowledge about and hasn't come up in any repair topics or videos I've seen for RGB/Arcade monitors. For some odd reason, it appears that the entire RGB color spectrum being output by the monitor has shifted. It appears to be like this: Reds are outputting as Green, Greens as Blues, and Blues as Reds. Consequentially, other colors have shifted as well including Yellows --> Cyan and so on. There are also some uniformity issues in the colors displayed in certain areas of the monitor as well (convergence, maybe?).

*Note: For the following statements, I have included a .zip folder containing the RAW screenshots/footage of tests I've done with the monitor. The footage has audio/playback speed issues that I can only assume was a failure of the 60fps capture mode, but it still demonstrates the issues with the monitor. They are in the following order:

1. Videos of Ocarina of Time via unmodded N64 over composite (Video 1).
2. Video and assorted screenshots of Super Mario 64 via unmodded N64 over composite (Video 1).
3. Video and assorted screenshots of Sonic Megamix V4.0 (Sega CD) via native RGBs from a Model 2 Genesis (RGB2 with composite video sync run through built-in retrogamingcables.co.uk sync stripper EuroSCART to BNC breakout cable).
4. Assorted screenshots of 480p VGA output from my HP Laptop to the XM29 Monitor (RGB1 at 800x600).


Downloadable via Mediafire here: http://www.mediafire.com/download/iu4yl ... -+Copy.zip


I have confirmed this issue is present on all input modes that I have been able to test (everything but S-video as I lack a source) so the input jacks are likely not the issue and I estimate it is probably closer to an intermediate stage between the inputs and the color guns themselves. I suppose my first step after posting this topic would be to seek out a service manual that I pray has some circuit diagrams for the chassis boards and investing in some better test equipment than my cheap multimeter.

It also does not appear to be a purity error as multiple degauss attempts have done little to nothing for the issues witnessed as seen in my footage (unless I need a stronger coil than the internal circuitry's, which I doubt).

Interestingly, there is a small portion of the monitor that actually does appear to be displaying colors in the proper manner in the very bottom-right corner of the monitor (which led me to the multiple vain degauss attempts). Screenshots:

http://puu.sh/k405J/98eeb2f317.JPG

http://puu.sh/k4072/07dfcc60da.JPG

http://puu.sh/k418r/c904a6a548.png

http://puu.sh/k41cb/9f976b34b8.png

White appears to display properly as well in the bottom right area of the monitor which I've provided a closeup shot that can be zoomed in to show the individual Red, Green, and Blue within the shadow mask (on the blurry mess that is my taskbar clock in this case).

http://puu.sh/k40fd/d980a27123.png

When I tried testing the RGB1 port with my laptop's VGA output, I honestly was rather disappointed with the results, particularly in how blurry the image looked through the shadow mask (A lot of text onscreen is actually unreadable in that manner). I tried lowering the resolution to 800x600 instead of the default 1024x600 my laptop defaulted to, didn't improve much. Of course, the color issues are still present here as well which remains my primary concern. However, I'm not certain if the blurry image is typical of the XM29 for a 480p RGB source, but that is coming from someone who's only other RGB monitor has a Higher TVL (800 vs ~600?) AND is a BVM 14F5U, so I'm probably just asking a bit too much from a ~600TVL monitor circa 1996. Still it does do 480p which unfortunately, most BVMs can't, which is good incentive to get this fixed.


That is the current situation as it stands. My primary goal besides gathering informations and seeking insight from the users here about potential culprits is investing in more test equipment I can use to troubleshoot the multitude of chassis boards within the XM29 once I can get around to actually opening up this huge monitor. I will add test pattern footage/screenshots on the monitor to this post as soon as I can find my Sega CD copy of the 240p Test Suite.

(Overlarge embedded images changed to links -Ghegs)

[sixbynine]

I am by no means an expert and take this with a grain of salt but I’m pretty sure you need a stronger coil to degauss this thing.

[tacoguy64]

I dont know much about the technical aspect of NEC RGB monitors but I do have XP37 which is just the bigger and slightly different version of yours. But I will chime in on pc use.

You have to set your laptop to match the monitors highest resolution setting and refresh rate. It will make things go a whole lot smoother. You might have to the enable vsync option. The NEC does make for a decent pc monitor for the games ive tried but i havent done much extensive playing on the pc side of things yet.

[Omegaknuckles]

I dont know much about the technical aspect of NEC RGB monitors but I do have XP37 which is just the bigger and slightly different version of yours. But I will chime in on pc use.

You have to set your laptop to match the monitors highest resolution setting and refresh rate. It will make things go a whole lot smoother. You might have to the enable vsync option. The NEC does make for a decent pc monitor for the games ive tried but i havent done much extensive playing on the pc side of things yet.

I had also tried the auto-selected rate of 1024x700 and 1024x768 and niether did much for the quality. You could argue I'm having issues from trying to match a 4:3 monitor to a 16:9 LCD. Not sure if I had a specific vsync option in the display config for windows 7. I'll need to check that again.

On a sidenote, I found my 240p test suite copy and will update later today with screenshots of how this is affecting the color bars/other test patterns.

[viletim]

Omegaknuckles,

The PTC in the monitor's degauss circuit is probably faulty.

[Omegaknuckles]

I have updated the OP with the image output of the SMPTE color bars through the 240p test suite. Yeah...Doesn't look pretty.

In addition, I have screenshots of pure R,G,B, and white outputs which I will link to in a moment.

Omegaknuckles,

The PTC in the monitor's degauss circuit is probably faulty.

I will be sure to test that theory with an external degaussing coil, since even if that is what's causing the issue, chances are that with magnetization that appears that strong, the internal degaussing circuitry would probably be too weak to fix the problem, even if it were brand new.

I am aware now that it may also be another issue entirely, specifically potential damage to the shadow mask. Unfortunately, if that is the case, then it is completely out of my ability to repair or anybody's ability without access to the proper manufacturing equipment to rebuild the entire tube.

It appears at some point that the monitor may have taken a hit or have been dropped (probably during shipping to the previous owner. You know and I certainly know how UPS can be.) which could cause damage to the shadow mask which would explain the shifted color spectrum (also why more of it is towards the center of the screen instead of the edges). I must apologize for neglecting to show this earlier since it does have bearing on troubleshooting the issue.

Chassis Screenshots:


Crack visible on the top. Possibly occurred during shipping to previous owner.

http://puu.sh/k6510/c04b0031f6.JPG
http://puu.sh/k6539/f5d9942ece.JPG

Monitor 240p Test Suite Screenshots:


Self-explanatory


http://puu.sh/k65ax/ded1310a26.JPG
http://puu.sh/k65cV/190624ba0f.JPG


Pure "Red" output by 240p Test Suite


Pure "Green" output by 240p Test Suite


Pure "Blue" output by 240p Test Suite


I will update as soon as I can afford to get a hold of an external degaussing coil.
If anyone has any recommendations for a good one for a 29" CRT, that would be nice.

[viletim]

With this new evidence, I'd say the monitor was dropped upside down and the shadow mask shifted. That's why the discolouration is worse at the top. There's not much that can be done about that.

[Omegaknuckles]

Bad news. Was putting some video through to the XM29 while trying to test out how well I managed to integrate my Yahama A/V receiver for audio purposes and while switching from composite (Video1) to RGB2, a loud pop went off back in the tube which prompted me to immediately shut it down.

Several attempts to start later with a wait period to let the tube cool down has shown it is now incapable of generating a raster (tries to start the tube and sync the image but fails, black screen) due to whatever the aforementioned blown component was controlling. Since it's likely that this monitor already has irreversible damage to the shadow mask, and that the amount I will need to invest in soldering/desoldering equipment, electronics test equipment, and an external degaussing coil, it seems like a better incentive to invest that into a >=20" BVM, NEC, or equivalent monitor instead.

Even if I managed to troubleshoot the new problem with whatever blew in the monitor chassis, I'd only be granted the opportunity to attempt to see if the aforementioned discoloration is shadow mask damage or extremely heavy magnetization (which seems unlikely due to its concentration near the center) and if it's the former, it seems a bit of wasted effort.

I think the best thing I can really hope for now is to take this wasted XM29 to my electronics recycling center and give this monitor a proper burial. Hopefully this doesn't offend anyone but it's doubtful I can do much even with the aforementioned equipment since nobody I'm aware of rebuilds these tubes anyways. Thanks for the advice, everyone.

In the meantime, it is getting some use as a stand for my still well functional BVM 14F5U with great picture (and 85000+ Hours, surprisingly), so there's that at least.

[Ed Oscuro]

You might be able to salvage some parts from the inside, like the flyback. Some of the PCBs might be good too. Even the fans give some people trouble, so if those work, those could be saved too. I don't know if it'd be worth your time to part it out, but you could probably generate a few bux.

[Omegaknuckles]

Hm, good idea.

I'll certainly consider it if I can get my hands on a discharge probe for the anode. Incidentally, the fans, speakers, front LEDs, and rear
inputs all still work, it's just the raster generation issue on one of the boards and color issues with the tube.

[Omegaknuckles]

Update.

Upon advice of the previous poster here, I have successfully disassembled the NEC-XM2950 and parted out each set of boards. I've listed every part of the monitor that could still potentially be used with a few exceptions. The exceptions to this currently are the front panel controls (didn't feel like disassembling the front half of the chassis from the tube since all that's there is the power button, some LEDs, and the IR sensor.), The central Mainboards (3 boards with a lot of transformers including the HV Anode Transformer that weighs more than my scale can measure, I.E. >10lbs), and lastly, the tube itself (had shadow mask damage, taken to electronics recycling).

Not to be a shameless self-promoter, but for anyone who IS interested, as of 10/19/15, the listings for each PCB/Part are available here:

PWC-3856B H-OUT PWB HV High Voltage Board

PWC-3851A D3608M-01 Power Supply Board

PWC-3834 VIDEO PWB 72137342 CRT Neckboard

PWC-3837 Video I/O PWB

PWC-3836 PWC-3835 RGB I/O PWB + AC Socket

XM-2950 OEM Case Fans + OEM Groundplane + Misc Mainboard Connectors


I appreciate everyone's help. I'll do my best to work out the weighing issue with the mainboards soon (having difficulties since my car is out of commission, potentially permanently at this point due to rusting causing severe damage to a retaining part of the frame for a trailing arm) once I can get the board to a larger mailing scale than what I use at home.

[Hoagtech]

A beautiful TV and story. Too bad no happy endings. I'm hoping one day I can get a decent NEC 29. I am trying to get a 29" because I can't find the NEC 29 anywhere. I'm gonna try some salvage auctions. I know the Boeing auction is once a year. I wouldn't mind getting a graphics monitor either

[BuckoA51]

Now I know who keeps causing those eBay watched search alert e-mails then