LCD Projector Flicker

[JohnMac]

Hi Folks,

 

Please could someone explain why a LCD Projector should start flickering. Computer input to the projector is via 5 x 75 Ohm coaxial cables derived from a 15 way high density 'D' type connector. At present both screens of sync signals are joined together and taken to pin 10 in the connector.

 

The projector works but appears to have a flicker, I've been told that if one's got broken cables lost colour is obvious, if either of the syncs is wrong it just won't work....

 

Text from the projector menu is fine, as is the composite video input.

Is it possible to develop an earth loop between projector and computer / switcher? Would trying a different refresh / resolution setting on the computer?

 

Regards

 

John Macgregor.

[jason5d]

it could be a ground loop

[Jon@Edric-av]

it could be a ground loop

 

Good idea,

 

Easiest way to test this is to plug the projector and computer off the same socket and you can confirm or eliminate this possibility.

 

Another option could be: mains cable/lighting cable off dimmers or a hearing loop being laid too near the signal cable.

[Johnparrack]

please define the flicker! You can notice easily if you've lost either vertical or horizontal sync (H sync ..more often than not will give no image, and vertical will give you a fast rolling pic). Ground loop will usually be a bar slowly moving up the screen. Plus if the syncs are both good, has the projector been correctly pixel mapped, just in case what u've got is flickering pixels. Or another possibility could be that a lamps on its way out, usually giving a flicker.

 

If you are using a 15pin vga to 5 wire breakout cable then usually the cable order is RGBHV...sometimes some manufacturers put the syncs in rev order!

 

HIya Jon@Edric...How is everyone, I used to work @ Gerrards Cross from 1988-95, before I moved to blitz....say hello to Gareth and ne1 else who's still there that may know me. <_<

[JohnMac]

Thanks Jon,

Tried turning dimmer rack off; no effect, but induction loop worth investigating, as well as ground loop. I know the installation has three phase electrics running around it, so want to convince myself everything is on the same electrical phase.

 

Regards

 

John Mac.

 

A concurrent post has been automatically merged from this point on.

 

John,

 

My flicker is variations in intensity predominately on background of Power point presentation. The projector is new, so hope no problem with lamp. Will investigate tomorrow areas for investigation, Electrical Phase same at both ends (control room rack, & projector up on ceiling). Laptop computer driving projector off battery only, Laptop with mains power supply, have thought about fitting ferrite inductor ring to cable. Computer direct through switcher, computer video via VGA/cat5/VGA converters. At present can't think of anything else to try.

 

Regards

 

John Mac.

[KevinE]

I've had the odd MH lamp (from new or otherwise) just start to flicker annoyingly, it seems it's a failure mode they can get sometimes. Just one to bear in mind!

[adamharman]

Trying it with a short cable to a laptop running from it's battery should clear up any ground loop and interference possibilities.

You do get dodgy lamps sometimes so that is a possibility. Beware of very loud bangs not too long after the flicker starts. I had one go in a Barco 6400 which I bought 2nd hand. The flicker was only really noticable on bright images. The next night the lamp blew to bits!

[Johnparrack]

variations of background..so from possible over peaking whites to graduated blues..set contrast to its default value and brightness...sounds like the image is hitting a volt and knocking itself back...or if u've got a 5 wire da in the rig (especially extron) make sure its set to 0.7 not 1v......sorry if I'm teaching another egg sucking lesson...but ive worked with many who don't know what those switches are for...so apologies in advance..

[JohnMac]

Not at all, when in the land of the blind, the one-eyed man is king!

 

Always grateful for help and knowledge, opens up new avenues to explore and learn. Projector is supplied of an active VGA twin monitor splitter / driver, so signal to projector might be near its' upper thresholds.

 

I've assumed that the 5 x BNC inputs are internally terminated with 75 Ohm resistors, time to read to manual.....

Wasn't aware of the differences in TTL logic levels and analogue levels.

 

Didn't have time to explore today, fixing transposed pairs on Cat 5 wiring, and control room monitor.

(some interesting colours appear when the green and blue signals are transposed! ).

 

Thanks for all your comments

Regards

 

John Mac.

[JohnMac]

Thanks for all your helpful comments.

 

Looking closely at the image one could see the flicking was happening in bars. At the time was playing a DVD through the system and the sound had the characteristic hum of an earth loop. Turned projector off and unplugged its' local socket:- hum disappeared. ;)

 

Supplied projector on extension lead from control no hum, no flicker.........

Although the same electrical phase, different distribution boards had been used with separate routes back to main switch board.

 

Cure: have projector and DVD / Switcher on the same phase from the same distribution board.

 

Good old Blue Room thanks for your contributions. :** laughs out loud **:

 

Regards

 

John Mac.