CurtPalme.com Home Theater Forum

Alan Head · Joined: 07 Aug 2006 Posts: 38

I have a G90 which now has over 8000 hours on the tubes.

While using the projector this evening I saw a green horizontal band flash across the screen. The projector continued to work fine.

When I was finished viewing I thought I'd take a look inside the green lens to see if any damage was visible.

The phosphor looked fine but there was a lot of dust particles visible. The projector has been on the ceiling for 12 years so some dust is not surprising.

When I looked in the green tube I could see some bubbles. The red and blue tubes showed no sign of bubbles.

I tried to take a photo and looks like some glycol has escaped and dripped down the tube. I used a separate light source to light the tube as I moved it about you could clearly see shadows moving.

Is it possible that water has been absorbed by the glycol and is now forcing its way out of the chamber?

Can I remove some glycol to protect the tube from cracking or is it already too late?

Its not easy to see what is going on with the lense still in place. I can also see a line which looks like it might be some sort of residue on either the lens or the tube surface.

Any advice would be appreciated.

Alan

**Curt Palme** · Posted: Thu Dec 14, 2017 11:36 pm Post subject:

Super easy to do on the G90. Disconnect the wiring, HV lead from the splitter (do you know how to do that, there's a trick to it). Take the 4 brass colored Philips screws out around the tube, and pull the tube out the front. On the bottom of the tube you'll see a metal cover with about 16 screws on it. take all those out, and that's the fill chamber for the glycol. Drain some, assuming that the rubber bladder under the metal cover is bulging. you want to leave that chamber about 1/2 full. That will leave an air bubble in the system, but not enough so that it is visible through the tube face.

Even if the bubble is well above the tube phosphor, you can get a reflection off the bubble that will appear on the ceiling or floor. Harmless, but annoying.

In the 'advanced' section of the tech tips on the main page are full instructions on how to pull the tube. Sheesh, would have been faster to link you rather than writing a paragraph. Smile

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Your glycol is obviously murky anyway and needs changing. But for 8000 hours your green tube is in spectacular shape. I suspect you don't run your contrast very high.

At this point if the green tube's coolant is that murky then all three need to be done. You will see the difference and appreciate it.

The shadow and trail is probably not a leak, but is particulate contaminants that have fallen down in front of the tube face. Still more reason to replace the coolant.

Fresh coolant is CLEAR.

You can get ethylene glycol in quarts (or any size) from ebay vendors. If you can't find ethylene glycol, apparently the easier-to-find propylene glycol is an acceptable substitute but I've never actually tried that myself.

Propylene glycol has almost as good thermal properties and its refractive index is nearly the same. It'll work.

Alan Head · Joined: 07 Aug 2006 Posts: 38

Thanks for the advice, Curt and CMJohnson,

I took the green lens off today to investigate further.

The good news is that I was able to slide a cable tie through the LC Chamber above the rubber bladder with plenty of clearance and no resistance. So looks like I don't actually need to remove any glycol. There is no sign of any leaking Glycol anywhere around the tube, LC chamber or chassis of the projector.

The vertical run appears to be on the back of the C Element rather on the surface of the tube so hopefully I will be able to pull the C Element and clean it thoroughly when I have removed the tube to change the Glycol.

Would this be appropriate to replace the Glycol :-

1L MONO ETHYLENE GLYCOL / MEG / ETHANEDIOL 99.97% ANALYTICAL REAGENT GRADE

http://www.ebay.co.uk/itm/1L-MONO-ETHYLENE-GLYCOL-MEG-ETHANEDIOL-99-97-ANALYTICAL-REAGENT-GRADE/162394705142?hash=item25cf7a8cf6:g:j~cAAOSwtfhYoeCD

The other good news is that I am unable to see any sign of what I thought might have been a hairline crack starting.

It assume that the projector is still safe to run until I get around to changing the Glycol early next year?

P.S. I run contrast at 60, hence the relatively low wear for 8000+ hours.

Thanks again

Alan

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Oh, it'd be safe to run, but your picture quality can't be very good with murky glycol.

Yes, that glycol would be fine to use. I'm not sure of the exact amount needed per tube assembly, but a quart is more than enough for one, not enough for two.

Easy way to do glycol replacement: Get a 10 gallon plastic bucket with lid. Cut a big rectangular hole in it so you can support the
tube by the LC hardware with the tube neck in the bucket. Remove the C element, don't damage the O ring.

Clean the C element very gently. You don't want to scratch it on either side. Soap, water, and a microfiber cloth is what I recommend. Clean the chamber and tube face with soapy water, triple rinse, let it dry completely before adding glycol.

With the tube assembly placed in the holding bucket, add glycol, drop the C element in, check the glycol level, remove the C element, repeat until you've got a very small bubble (coin sized) or even no bubble and then secure it in place. You will probably get some spillage. Rinse it all off carefully. A hair dryer can be helpful.

Now place the tube assembly on its side on a newspaper and ignore it for a day. Check tomorrow for any drips on the paper.

When it's confirmed clean, dry, and leak free, it's ready to reinstall.

MAJOR word of caution: The most challenging part of removing a G90 tube assembly is dealing with the red high voltage lead.

It uses a twist lock connector at the high voltage splitter block.

If you simply yank it out you will break the connector and that would be very bad. There's no source of replacement connectors.

You have to push the cable into the splitter block with substantial force, twist it 90 degrees counter-clockwise, and then pull it out with light pressure.

It helps to pull the grey rubber boot back away from the splitter block. It will slide on the cable.

Alan Head · Joined: 07 Aug 2006 Posts: 38

Thanks for the advice guys.

I have now changed the glycol and the projector is running again.

The good news is that the vertical lines were on the surface of the tube and cleaned up perfectly.

Unfortunately I also discovered a scratch on the tube surface. it is very light and about 15mm long. it is at the edge of the tube about a quarter of the way along the horizontal edge of the tube, not near the corner and not near the tube support pads on the LC housing. It looks a bit like an eyelash but wont clean up. You can just feel it if you run your nail across it. This is the suspected start of a hairline crack I mentioned in the earlier post.

Is this something that can be ignored or is just a matter of time before it becomes a crack and implodes the tube?

Now that I know its there I will keep an eye on it to see if it grows.

I am trying to imagine how it got there. If there was pressure on the tube I can understand how it could crack the tube but not how pressure could slightly scratch it. I suspect / hope it may have been scratched at the time the P19LUG's were installed into the LC assembly (8700 hours ago) and that it has been there for 12 years unnoticed. My best guess / hope is that it was scratched while trimming excess silicon when the tube was fitted to the LC chamber.

Has anyone any experience of this sort of defect?

Should I be sourcing another green tube just in case?

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Tubes do NOT develop hairline cracks and blow up later.

The scratch you found is a scratch. It happens.

But it doesn't matter because it's almost half an inch out of the focal plane. You'll NEVER see it on the screen no matter how hard you look for it.