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brickcam · Jan 30, 2007, 02:21 AM

Hi all. I have an iBook G4 1.33 MHz using the Screen Spanning Doc and a mini-DVI to VGA adaptor with a 17" CRT. I love the set-up. I couldn't go back to just one screen.

My problem is that all three of the CRTs I've used in this set-up have displayed the same symptom: mild (to moderate) shaking of the image, as if the hold is slightly off. I thought it might be component failure, but this last one acted fine in the thrift store and then when I got it home it was still fine, and only now, a day or two later, it is shaking. ???? I am unsure what large magnetic fields I might have nearby. I have the CRT balanced on a computer desk of wood and metal, the inkjet printer is very close by (on top on a shelf), the ibook is about 6" away, and my router, cable modem, ext hd, power strips etc are about 2' away. The cable plug in the wall is about 2' away as well.

I know this is a bit electrical and abstract for macnn but I hoped there might be a gearhead who could help me. I appreciate any of your input and I'll gladly respond to questions to clarify.

Amusingly, it's stopped shaking at the moment. I can't predict it, but I can say that it seems to get worse with a particular monitor as time goes on. That said, they were all purchased used.

Thanks for reading.

MichiganRich · Jan 31, 2007, 12:01 AM

There's an area at work about 20 feet square that causes any CRT within it to get jumpy. It's not fixable at all for us, lord knows what 'fields' are around that causes it. Strangely, the lower the refresh rate, the less jumpy the monitors are. 100hz and the monitor jumps like its on a trampoline, 60hz and it's usable, but with the typical 60hz tradeoffs.

brickcam · Jan 31, 2007, 02:28 PM

Originally Posted by MichiganRich

There's an area at work about 20 feet square that causes any CRT within it to get jumpy. It's not fixable at all for us, lord knows what 'fields' are around that causes it. Strangely, the lower the refresh rate, the less jumpy the monitors are. 100hz and the monitor jumps like its on a trampoline, 60hz and it's usable, but with the typical 60hz tradeoffs.

Thanks for responding. I will try the bit about refresh rates... that surprises me. I would think higher would be more stable. Anyway, I think I've been running them at 85 Hz. Cheers.

LV426 · Feb 9, 2007, 09:14 PM

I turned my refresh rate down to 60Hz and have no problems now. What kind of 60Hz trade offs are there MichiganRich?

Apfhex · Feb 9, 2007, 09:54 PM

Have you tried moving them to somewhere else in your home, still in use with the iBook?

I used to have problems with a dishwasher and CRTs, quit annoying.

brickcam · Feb 9, 2007, 10:02 PM

Originally Posted by Apfhex

Have you tried moving them to somewhere else in your home, still in use with the iBook?

I used to have problems with a dishwasher and CRTs, quit annoying.

Yes, I have moved them around some: it's difficult to troubleshoot since the problem is intermittent. Best that I can tell, it happens throughout my (small) flat. Thanks for your input.

ghporter · Feb 10, 2007, 09:26 AM

Keeping your CRT out of strong electrical fields, and more importantly keeping your CRT CABLES out of those fields is a good start. And using well-shielded cables will help too. The issue, if it was resolved by changing to a 60Hz refresh rate, could have simply been that the monitor was refreshing at a rate that made your florescent lighting interact with the screen refresh. Or it could have been that there was a strong 60Hz signal in the area, like a large power cable in the wall or floor. Either way, if 60Hz works, stick with it. The days of "I can only get certain screen resolutions at certain refresh rates" are fading fast, and most CRTs are still more capable than most video cards, so there are few tradeoffs with modern video cards and relatively current CRTs.

MichiganRich · Feb 10, 2007, 02:15 PM

LV426-

The '60hz tradeoffs' I mentioned are based on the fact that I find 60hz refresh rates to be slow enough to be noticeable. It's a faint 'flickery' quality when looking directly at the screen, it's not as 'solid' as the image would be at 85 or 100 or greater. It's hard to explain but visible I guess.

I find that it is more noticeable when looking at the screen out of the corner of my eye. It's quite apparent if the screen is in your peripheral vision (no puns intended).

LV426 · Feb 10, 2007, 06:06 PM

Why Would My Screen Shake At A Lower Refresh Rate? At 100 Mhz It Is Very Noticable.