CurtPalme.com Home Theater Forum

winny · Posted: Wed Jun 03, 2015 12:54 pm Post subject: Spot burn, delamination or dust?

I have discovered two black dots on the green tube. They only manifest themselves during white scenes but being close to the center, they are noticeable.

I was under the impression that the focus is shallow and on the phosphor layer but would something on the outside of the glass show up fairly in focus?

Get new tube?

**Curt Palme** · Posted: Wed Jun 03, 2015 8:09 pm Post subject:

If the dot does not move with raster shift, then I'd guess it's the tube.

CasetheCorvetteman · Joined: 09 Nov 2008 Posts: 6326 Location: Australia

Or on the lens

winny · Posted: Thu Jun 04, 2015 8:24 am Post subject:

Wouldn't the lens be too far out of focus plane for that to be projected as such small dots and fairly sharp?
Dust/spec on the front of the tube ?

CasetheCorvetteman · Joined: 09 Nov 2008 Posts: 6326 Location: Australia

Possibly, youd have to shine a torch in there and see if its on the phosphor or the glass

jbmeyer13 · Joined: 03 Dec 2010 Posts: 1135

That's either something on the inside of the C-element, phosphor delamination or a defect in the tube glass itself. I bought a brand new tube last year which exhibited the same issue and after draining the glycol, cleaning the c-element and tube glass I discovered under close examination that it was actually a defect in the glass. Steve Flynn told me that he used to send back a fair number of tubes to VDC after QC'ing them and finding these types of issues.

I've seen a spot burn and it doesn't look like that.

Tim in Phoenix · Joined: 21 Oct 2006 Posts: 4409 Location: Phoenix

Guys

Looks like spot burn, and I would look into that tube at power-off and see if spot-kill has problems. I would not replace the tube until the problem that damaged it gets corrected.

winny · Posted: Wed Jun 10, 2015 8:12 am Post subject:

As for spot kill, it goes from full brightness to black before any collapse/shrinking of the image area. Just the afterglow visible. My eyes did start to clip/distort though. Do I need to check more thoroughly that that, like film it with very open shutter and check frame by frame?

Took the lens off and it certanly looks like the phosphor. Sad

Bloody difficult to take a photo of without a full manual camera. Refresh rate of projector didn't match or wasn't too out of sync to give me a complete picture and the active scan lines being way brighter than the rest confused the camera.

**Curt Palme** · Posted: Wed Jun 10, 2015 8:30 pm Post subject:

I disagree with jb, I've seen many tubes with phosphor flaws that look exactly like your original images on the top.. including spot burns that I've caused myself.

winny · Posted: Wed Jun 10, 2015 9:02 pm Post subject:

So spot burn is still on the table? High speed video camera set to full open?

jbmeyer13 · Joined: 03 Dec 2010 Posts: 1135

**Curt Palme** · Posted: Wed Jun 10, 2015 11:32 pm Post subject:

Yes, exactly! I've got two new (old stock) blues here that arc when pushed with contrast over 80. It's an internal arcing right at the HV lead, but inside the tube. Completely useless, which is a shame.