Home Theater sales, calibration, service, and discussion forum. Hundreds of free manuals & setup tips.

Sign up and receive the latest newsletters by email!     Join the Forum discussions!    
    Site Map  
Home Products
For Sale
Links Contact
CRT Primer
Troubleshooting Tips
Mounting Methods
Definitive CRT
Projector Setup Guide
Tube/Raster Setup
Tube Condition (Wear)
Projector Rankings
Video Processors
Ampro 1500/2000
Ampro 2300/2600
Ampro 3600/4600
Barco (Older Analog)
Barco 70x/Cine7  
Barco 500/800/801
Barco 808/Cine8
Barco 120x/Cine9
Dwin 500/700
Electrohome ECP 
Electrohome Marquee 
Panasonic 108x
Sony 10xx
Sony 125x/127x
Sony 1292
Sony D50
Sony G70
Sony G90
Zenith 841/851
Zenith 895/900
Zenith 1200

Venting Liquid Coupled (LC) tubes

  Back to Advanced Procedures Index



The following procedure and pictures were provided by Tim Martin.  Thanks Tim!  While it was written with Marquee LC projectors in mind, it's also pertinent for any LC projector. 

Looking for a similar procedure for air coupled (AC) projectors?  See here.

For definitions of c-element, liquid coupling (LC), or air coupling (AC), see this page.


Those with LC Marquees, Vision Ones and Madrigal MP9s (and other projectors with LC tubes) will want to check their tubes on occasion so pressure does not build up in the fluid chamber; you don't need this:


If ceiling mounted, lay down some plastic sheet like five feet square.

The plate across all three tubes can be removed to access the vent holes. It will be necessary to spread the cabinet sides a bit, so remove a screw for the "spreader bar" or remove the bar entirely:

The metal plate holds the sides in, so remove those screws, one each side:

The are two screws in the back into the heatsink, remove those if necessary. It should not be necessary to pull the sides if the unit is ceiling mounted.

The plate is held to the tubes, and has x-ray shielding attached, so remove four Allen head bolts, 3/16" wrench; pins stick out of the plate into the tube castings so some prying and manoeuvring is needed:

With the plate removed, you can see the rubber bellows (black between the castings) and two fill-holes on each tube. If the bellows is hard to the touch then some glycol should come out as a precaution. Glycol sucks water vapour right through the rubber, no joke!

The fill-hole plugs are tiny Allen screws and gaskets, 5/64" if I recall right:

Glycol can pressurize and shoot out with considerable force so watch out!!!!!!!!! Have a bucket directly underneath, and goggles are not a bad idea. Remove enough glycol so the rubber is spongy to the touch with the plug reinstalled.

When you vent something like this that is ceiling mounted and the fill-hole plugs are on the bottom, once you remove the plugs the glycol is thick enough that once the excess glycol under pressure comes out, the rest will stay in the tube.  Don't worry - you won't completely empty the tube! When I am draining glycol on loose tubes, even when upside-down, if I remove both fill-hole plugs, there are just a few drops or none if not pressurized, the glycol is quite oily and it stays put if air is not coming in. The fill-holes are tiny, maybe 2mm. What is needed is air to push the glycol out, and your garden variety canned air with a thin tube on the nozzle is just the air needed to drain effectively. To vent an ounce on a ceiling, pushing on the bellows should suffice.

This procedure is for ceiling (upside down) only. Table standing chassis are best vented with the tubes removed or you risk glycol going everywhere. If you want less work than that, remove the top plate and flip the unit upside down, very carefully, so the fill holes extend over the edge of a table. The unit is quite front-heavy so do this with helpers or some method to secure the back end against falling off the table.

You do not ever want to remove fill-hole plugs on a pressurized tube sitting in a projector that is upright; glycol could shoot out with considerable force and trash the chassis!

Good luck!

Did you find this information useful? Please consider making a donation to help defray the cost of managing and hosting future articles, tips, and documents.     

Or purchase from and a small percentage automatically goes to support this site at no extra cost to you! Visit their Blu-ray and DVD stores for sales. Want to show off your home theater? See our Blu-ray Release List & Must-Have Titles. Shop at and support our site!


Copyright All Rights Reserved.