Help please! It's driving me nuts!



Hi Everybody!

We've recently bought a Epson EMPS-4 projector, and roof mounted it. Have a Yamaha amplifier, as well as a Macmini, both needed to be linked to the projector.

Connections from the Yamaha amp in the form of a RCA cable (only video), and from the MacMini VGA-over-Cat-5.

Following scenario... ducting for the cabling - contains RCA cable, CAT5 (unshielded - shielded VERY expensive!), as well as power cable (220V).

Now I'm experiencing some problems.. The macmini images have ghost-like replicas just to the right of the original image on the projection, and there's marked interference from the power cable on the RCA video too - scrolling lines on the black projected.

The length of the RCA is about 25metres, and the length of the CAT5 is also in the region of 25 metres.

I have removed the power cable from the ducting, but it only solved the scrolling bars on the black from the RCA-video... NOT the problem of the ghost images...

Does anybody know what the limits (lengthwise) are for Cat5-VGA? Limits on the RCA (lengthwise)?

Any and all help appreciated!

Thanx :)


Novice Member
This could be a result of what is called 'skew' on the CAT5e.

The way the cable twists within the CAT5e results in each pair being a slightly different lenght. Hence the ghost type images as the different video images are arriving at slightly different times.

Simple solution is, do some research on which pairs get shorter and manually make them longer by leaving a longer tail.

The other option is a piece of electronics that buffers the leading signals to bring everything back into sync, not sure on cost, but I would guess expencive.




Thanx for the reply. That's all good and well - I understand that the one signal arrives before the other signal - but now a couple of new problems... how do I determine which wire to extend, and by how much? Surely there should be a formulae for this? Searched high and low for SKEW CORRECTION formulaes and stuff on the 'net, but with no luck :( Any ideas?

Joe Fernand

Distinguished Member
AVForums Sponsor
Hello tinusb

I take if you have linked the Mac mini to the Projector on a short 'VGA' cable to confirm it does not produce this same ghost?

Have you tried a shorter version of the VGA over CAT5 cable to see if it works at the resolution you require?

What is it your viewing via the AV Receiver - projecting a Composite video signal is poor at the best of times never mind that you have a 25m cable run plus interference from your power cord.




I have viewed the connection from the MacMini with a shorter VGA cable (the one supplied with the projector) and the display has been perfect. Don't have the necessary plugs to make a shorter version of the cable. My DVD player connects to my AV receiver via coax or fibre optic for the DTS sound... the connection from the AV receiver is in the form of a single RCA connection, labelled: 'Monitor Out'.

Thanx for the help! :)


Active Member
I see two problems:

1. Power cable in the same duct that causes interference (which is unsafe and possibly a violation of the electrical wiring code, too, but I promise not to tell anyone ;) )

2. CAT cable not shielded, which makes things really bad in combination with #1.

The composite connection is not the best option either as this is the worst signal type, S-Video or RGB/YUV would be better.

But to be certain that the power cable is the source of all problems - can you try to connect the projector via a different (temporary) power cable? I mean just go straight from any wall outlet to the projector and see if things improve or not.

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