Display Problems

[Raiken]

Hi all. Recently my iMac has been having some very strange display problems. For some reason in static images the redscale appears to have horizontal lines running through it. This can make photos look very grainy and pixelated, but it all depends on how much red there is. For example on images mainly comprising of blue and green, the defect is hard to notice. This problem applies to all programs, ie safari, itunes etc, and is not exclusive to an image viewer.

Strangely when watching movies on quicktime, there are still problems, but they're different than before. In movies there appear to be lots of, well it's hard to describe, but lots of small green capsules lined up on the screen.

I would have normally thought there's a fault with the monitor, but since the nature of the defects seem to vary depending on whether the images are moving or not I'm thinking something might be wrong with the video card.

The problems only manifested themselves last night. I think they may have come from a virus or soemthing in a few avi files I downloaded. They played fine themselves and there didn't see to be a problem, but it's the last thing I downloaded on to the mac before the problem arose. Since then all movie files (included those avis) seem to be affected in the same way.

Any ideas as to what's going on exactly would be much appreciated, as I'm completely stumped. Thanks.

 

[Raiken]

Ok, I realised that the ''green capsule'' problem was related to quicktime, since on realplayer the problem is not present. However the ''graininess and lines'' in redscale problem is still there, and that's constantly present in all programs.

 

[Kyomii]

Go to system preferences and monitor preferences, - what is the resolution set at and is it set to millions of colours? If resolution is high enough and colours are millions then....

Make a new user with admin priviledges and then restart your computer and log into the new account - do you still have the same problem?

If you do, run the hardware test that came with your Mac - it should be on the system CD's/DVD's.

It is not likely to be a virus though - so don't worry about that!

 

[Raiken]

Hi, many thanks for the help. I had tried those, but in the end I realised the problem stemmed from electromagnetic interference from my new wireless logitech mouse.

I had tried turning it off before, to no effect, but realised there might some kind of residual interference, so left it completely disconnected for a whole day and now the problem is completely gone. Makes sense that reds were affected the most since they're on the lower end of the E.M. spectrum.

 

[Kyomii]

I am sorry to disagree, but I would not have thought a mouse could cause that *amount* of interference at all, the mouse receiver simply doesn't emit that much EMI, and should operate on a high frequency being a new mouse. (2.4G)

It is in-fact, the other way around. Your monitor is far far more likely to cause interference of mouse operation, given the high rate of emitting interference from such a powerful device, rather than the other way around.

I have built 100's of systems and have several systems here - and I have never ever seen that amount of interference from a wireless mouse in the 11 years since I started.

Is the mouse RF or IR or bluetooth? How old is your iMac? Is it TFT or CRT? EMI is far more likely in a CRT monitor, and interference is more likely in RF mice because of low frequency operation.

If you turned off your computer for a day and this solved the issue, it is more likely surge spikes from your socket causing the monitor issue - have you got it shielded?

If your mouse did cause that amount of interference, I would take it back, because it is obviously faulty.

 

[Raiken]

Well this the mouse I'm using:

http://www.morecomputers.co.uk/extra.asp?pn=910-000241

And the iMac is about 2 years old, so it's definitely not CRT. I'm pretty sure the problem didn't stem from a power surge, as the other electronics in the room seem unaffected, and I didn't turn the mac off when the problem went away.

I wouldn't have thought a cordless mouse would be the cause of the problems either, but it seemed like too much of a coincidence that the problems started occuring a few days after I connected it, and then seemed to dissapear when I took it out. I've been trying to connect the wireless mouse via the Mac's own bluetooth now, but it doesn't seem to recognise it, as I'm trying to avoid using the 2.4ghz receiver.

Ofcourse, this could all be coincidental...and the problem is more likely to be the 37'' LCD tv that's right next the imac, but they'd been working in close proximity to another for about a month prior without any issues.