How can I fix my CRT display's ghosting?

December 13, 2006 8:34 PM

I just brought home a big o' 21" viewsonic P815 monitor. It didn’t have the monitor cable, so I used a crappy one I had. I’m noticing a lot of odd “shadow” effects, especially with black text on a white background- the text is clear, but there’s a very light grey echo to the right of it, then a lighter echo to the right of that, and so on. It reminds me of cable "ghosting." My question: is it a cable problem or a monitor problem?

If the monitors’s bad, no big loss- it was free- but I don’t want to waste the money on a cable if it won’t make a difference.
Bonus Question: if I do get a cable, will it make a difference which input set I use (the monitor has a standard SVGA jack and seperate RGB BNC connector jacks)?

posted by dogwelder to Computers & Internet (16 answers total)

Cable quality is critical to video quality...I've run into problems like that even on LCD monitors, when using cheap extension cables. Get a good quality, well shielded cable and try it. You might be surprised.

Too long a cable can also cause similar problems.

For the bonus: Theoretically, the separate RGB jacks are supposed to give better color, but I think you might solve your basic problem with a better standard VGA cable.
posted by pjern at 8:38 PM on December 13, 2006

If you used a crappy, poorly shielded cable, it's entirely possible that is the culprit (this sort of ghosting does happen with poor cables, especially on higher-frequency monitors).

Of course, it may also be the monitor.

If you take the cable, move it around, coil it, and so on, does the ghosting change at all? If so, it's probably the cable. If you can get a good one from a shop with a decent return policy, you can find out pretty easily.
posted by toxic at 8:39 PM on December 13, 2006

Response by poster: toxic- a just moved the cable, and some stuff shifted- seems like it's worth it to invest in a new one.
posted by dogwelder at 8:42 PM on December 13, 2006

This is a tube-beast, right? Have you tried Degaussing it?

But a good cable can make a difference too, can you borrow someone else's for a day or two?
posted by jkaczor at 8:47 PM on December 13, 2006

Response by poster: done the degauss dance- the ghosts live. This would be a two-second thing to figure out if the built-in config menu had some black on it somewhere, anywhere...
posted by dogwelder at 8:54 PM on December 13, 2006

You should definitely use RGB cables. A normal VGA cable will look much, much worse.
posted by Steven C. Den Beste at 9:13 PM on December 13, 2006

Yes. Note, also, that video cards differ in their analog output quality.
posted by rbs at 9:16 PM on December 13, 2006

The shielding is what's critical, as others have said. I had exactly the same problem with a new monitor a long time ago. You don't need to buy the uber-expensive cables from Best Buy, any shielded cable from something like a college bookstore will do. They tend to sell them much more cheaply than Best Buy's nuclear-grade Belkin cables.
posted by ontic at 9:22 PM on December 13, 2006

Response by poster: I just diagnosed the problem using metafilter's front page! The monitors OSD pages are blue with white letters, just like the mefi page (but brighter). On MeFi- ghosts. on the menu- no ghosts!

Metafilter is my new favorite diagnostic tool! I'm heading to Fry's tomorrow!
posted by dogwelder at 9:45 PM on December 13, 2006

Does the cable you are using have 'thick bulges' at either end? I've seen some cheap VGA cables that don't have it.

Those are 'EMI clamp filters' which can prevent stray interference from leaking in - you could buy separately, but probably would be better if built-in.

One last silly question - but you have 'screwed-in' both ends firmly, right?
posted by jkaczor at 9:48 PM on December 13, 2006

Response by poster: jkaczor- no filters. I'm guessing clamp filters wouldn't be much less than the cable, so I'm just going to get the cable. I'll probably go nuts and get the BNC connector one. And yes, the screws are tight- but I'm glad you asked. Sometimes the simple solutions get overlooked.
posted by dogwelder at 10:10 PM on December 13, 2006

Well - if you have BNC output on your video card - go fo it.

'Back-in-the-day', when I used to sell & support high-end CAD/CAM workstations - that's what all the serious users required.

Aww, you can tell I've been doing support for the last year ;-)
posted by jkaczor at 10:51 PM on December 13, 2006

It doesn't require a special BNC output on the display card. An RGB cable has BNC cables at the monitor end but exactly the same connector at the computer end as a VGA cable. It plugs into exactly the same plug on the computer.
posted by Steven C. Den Beste at 11:14 PM on December 13, 2006

The echo you're seeing is called ringing. It's caused by the signal bouncing back and forth in the cable, which in turn is caused by an impedance mismatch between your crappy cable and the VGA outputs and inputs you're plugging it into. It's got nothing to do with external interference.

If you get yourself a cable that actually meets VGA specs, the problem should go away. In the meantime, you should be able to make it somewhat less noticeable by lowering your display's refresh rate to the slowest you can stand; the frequency of the ringing and hence the time between peaks is fixed by the length of your cable, and at lower refresh rates, the ringing peaks will appear closer together on the screen.
posted by flabdablet at 1:52 AM on December 14, 2006

If you're a roll-your-own kinda guy, and you want to run your video signal any kind of distance, read this thread before plunking down any kind of dollars on high end cabling.
posted by flabdablet at 2:42 AM on December 14, 2006

If you can get a good one from a shop with a decent return policy, you can find out pretty easily.

Do this.
posted by smackfu at 7:14 AM on December 14, 2006