Over head projector

[PhilB]

I've recently installed a single 13amp socket for an over head projector the socket is spurred off the ring main. When the projector is switched on it projects OK but the screen has quite a lot of white horizontal lines and interference on it but when I unplug the projector from the single 13amp socket and plug it into an extension it's perfect. The extension lead is plugged into the same ring main socket that the single 13amp socket is wired into. I've also tried wiring the single socket into another ring main nearby but it still has the same interference.

 

[MisterE]

Hi, are we talking a digital video projector or an "old" overhead projector for transparencies?

If digital projector :-
Was the video lead connected when you tested the output?
If so, is there a decent distance between the power cabling and the video lead?
Is the video lead screened?

 

[Rockingit]

Earth fault somewhere - and remember to check at the signal source as well.

 

[Lucien Nunes]

Ideally the projector should be supplied from the same final circuit as any analogue signal source(s) that feed it (e.g. component and RGB), preferably from nearby and cabled along similar routes. This will avoid circulating ground currents inducing hum into the video circuit. Hum is usually fairly recognisable as a symptom and I wouldn't describe it as horizontal white lines, so it is not clear what kind of source is creating the interference.

Can you post a picture, and confirm what signal sources are in use and how their mains supply relates to that of the proj?
Does the same patterning occur with a DVI or HDMI source as with RGB or YUV analogue?
Are any twisted-pair extenders in use in the projector signal lines?
Is the projector new?
What is Zs at the new socket outlet?

I'm a bit tempted to agree with Rockingit but presumably the new socket has just been tested so we wouldn't immediately assume that to be the culprit. But a lost CPC at the signal source end is quite a possibility.

Sorry, lots of questions...

 

[Rockingit]

Whilst I'm by no means a complete expert Vidiot (to use the staging worlds term of endearment for the AV guys), from experience when you get this type of issue it's almost always caused by a lack of sync in a signal, and as the signal cable which links the two ends is common across both the signal ground and 'true'/reference earth, that's almost certainly where the problem is. I'd put a pint on it.

 

[ImpededLoop]

Does the supply for the single socket run next to the VGA cable for the projector?

I've also seen problems caused by the VGA cable being too close to high frequency fluorescent light fittings, but you seem to have narrowed the problem down to the mains supply.

 

[davesparks]

Knowing how challenging it can be to actually connect a VGA connector I'd be looking for a loose/shorted ground or sync connection.
Did you use solder bucket VGA connectors or a screw terminal breakout?

 

[PhilB]

Thank you to all the replies, now I am confused. The projector is digital and was installed by a company specialising in overhead projectors all I've done provided a supply. The projector and the IT equipment controlling/linked to it are both on the same ring. The 2.5m T&E cable is above a suspended ceiling and parts of that cable do run fairly close to recessed modular fluorescents. The Zs is exactly one Ohm which is within the 1.15 for a 32amp B type MCB. I have installed another projector supply in another room which is remote from any fluorescent lighting etc so I'll take a look at that issue first. Thanks again to all, Phil