Green 'tearing' on HD projector when image contains pure black or pure white

[AngryTechnician]

I installed a Mitsubishi FD630U projector in to one of our halls over the holiday, and have it connected to a desktop's second monitor output. The second monitor output is DisplayPort, so I've used a DisplayPort to HDMI cable to connect it to the projector's HDMI port.

 

This works fine, except in one scenario: whenever there is a significant amount (anything more than about 15%) of pure black or pure white on the screen, a green horizontal 'tearing' effect appears on that part of the image, and the rest of the image also experiences some interference (not green, more like intermittent missing pixels). This causes a problem with PowerPoint, unless you set the background to slightly off-whiter (or slightly off-black). In extreme cases, the projector will actually lose sync entirely, then flick back a second later.

 

The rest of the time, the image is perfect. This happens regardless of image resolution or whether the computer is in duplicate or extended. I've got different cabling coming in on Monday to test, and my next step will be to try a different computer, but am wondering in the meantime if anyone has seen this sort of thing before and knows what might be causing it?

[Marc-Engineer]

What length is your HDMI? it is only reliable to 20mtr above that you need to amplifi the signal.

A second problem could be cheap HDMI leads some i have seen are of very poor quality and would give you this problem.

 

Marc

Projector Engineer

[AngryTechnician]

HDMI length is 15m. Not the most expensive cable in the world but I deliberately didn't go for a cheap option either. Like I said, I have some different cables coming in as I am leaning towards a cabling problem myself, as the interference looks very similar to that on my office computer a couple of months back that I found was down to a dodgy DVI cable.

[tommej]

Tried it on the primary output? (I assume this one isn't DisplayPort?)

[AngryTechnician]

The primary is integrated (it's an all-in-one, a Lenovo M90z).

[Marc-Engineer]

HDMI DVI-d same cable different plug i have had problems with several supposedly better cables and dont be fooled by "gold" connectors gold colour maybe...lol

Try if you can the projector with a much shorter cable, dvd player or computer on steps if projector is mounted high.

 

Marc

Projector Engineer

[AngryTechnician]

Just realised that I never posted the solution to this: when I dropped the refresh rate on the external output from 60Hz to 30Hz, the problem immediately went away. The projector specs say it supports 1920x1080 at 60Hz, but it only works reliably for us on this resolution at 30Hz. Nobody can tell the difference on PowerPoint, and it's difficult to tell even with HD video, so that's what it's been set on ever since.