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G90, green channel has noisy background and spot kill fail
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cmjohnson




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


PostLink    Posted: Wed Jun 07, 2017 10:00 pm    Post subject: G90, green channel has noisy background and spot kill fail Reply with quote


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Curt or any other G90 technician, I'm asking for your greater experience here.

I'm checking out a G90 for possible sale, and the one I'm working on right now has a noisy green video amplifier and its spot kill function is not working. On shutdown it creates a very pretty moving snowflake-ish pattern that grows until it fades out, only in the green channel.

Contrast levels have been kept low and there has not been any tube damage yet but clearly this is not something I can sell unless I find and fix the problem.

With no picture, even with brightness, contrast, and even gain and drive set to zero, you can still see a faint green raster on the screen (much brighter when looking at the tube face) and it's rather noisy.

I have a spare parts unit. But since there's a lot more to a G90's video system than with a Marquee, I'm looking for input
on what board(s) should be changed out.

I'm also getting a few HV snaps near the HV splitter block on startup, but they don't continue. After about a second it makes no more snaps. Powering up the unit in the dark did not help me to localize the snapping. No arcs or sparks were seen.
And I'm not about to repeat that until the spotkill issue is taken care of anyway.

This is a brand new tube in this unit. The other tubes are minty but have at least a couple of hours on them.

Yeah, I have five other G90s to play with, but I'd rather find and fix the problems rather than pile up projectors that need minor repairs but aren't safe to run as they are now.
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Curt Palme
CRT Tech



Joined: 08 Mar 2006
Posts: 24296
Location: Langley, BC

TV/Projector: All of them!


PostLink    Posted: Wed Jun 07, 2017 11:14 pm    Post subject: Reply with quote

Both are usually due to contamination in the tube. Seen it all too often. Put a worn tube in its place, that's the quick and easy fix, and I'll bet both issues are gone instantly.

Spot kill failure will nuke the tube. the 'fireworks' display with no burn at turnoff indicates a bad tube.
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cmjohnson




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


PostLink    Posted: Thu Jun 08, 2017 12:13 am    Post subject: Reply with quote

OK, but that doesn't explain the noisy background raster?

The high noise background is limited only to the raster. If that were a noisy tube issue, I would expect
it to occur over the whole phosphor area. That it's only in the scanned raster tells me I have a noisy amp,
but each color channel in a G90 has not less than four circuit boards involved.


I'll swap the tube in question into another chassis that is known to not have any issues.

If it still happens then it probably is something with the tube, and then I'll test it in a Marquee
without removing it from the G90 LC assembly. If it still does the wierdness, then I will just
live with it as it probably won't result in a phosphor burn any time soon. It really doesn't get
THAT bright anyway.
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gregstv




Joined: 27 Aug 2007
Posts: 628
Location: Australia


PostLink    Posted: Thu Jun 08, 2017 12:41 am    Post subject: Reply with quote

I had the same issue with a XG75. It was the tube.
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Curt Palme
CRT Tech



Joined: 08 Mar 2006
Posts: 24296
Location: Langley, BC

TV/Projector: All of them!


PostLink    Posted: Thu Jun 08, 2017 1:18 am    Post subject: Reply with quote

Yes it does, that's contamination in the electron gun. The two are related faults, seen it many times.
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cmjohnson




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


PostLink    Posted: Thu Jun 08, 2017 2:44 am    Post subject: Reply with quote

I'll confirm it later tonight, or tomorrow. Then see if maybe it's usable in a Marquee, since apparently G90s are very demanding
of tube quality. Maybe run it thru the short clearing feature on a Sencore restorer if necessary.
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cmjohnson




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


PostLink    Posted: Thu Jun 08, 2017 4:23 am    Post subject: Reply with quote

To my surprise, kind of, it turned out that the tube is indeed the problem.

I swapped it out for a known good green out of another G90, and none of the described problems appeared.

Hopefully that green tube is still OK for Marquee usage. I'll have to find out.

As I gather, G90s make harder demands on the performance of the electron gun assembly than other projectors,
but I don't have the specific data on HOW.
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Curt Palme
CRT Tech



Joined: 08 Mar 2006
Posts: 24296
Location: Langley, BC

TV/Projector: All of them!


PostLink    Posted: Thu Jun 08, 2017 1:39 pm    Post subject: Reply with quote

AFAIK, it has nothing to do with that, for years we've simply called it 'contamination of the electron gun'
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cmjohnson




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


PostLink    Posted: Thu Jun 08, 2017 2:57 pm    Post subject: Reply with quote

I'd REALLY like to explore what's really happening with this tube that causes this effect.

It's just a personality trait: I like to know the deeper reason for something. Saying it's contaminated doesn't quite satisfy me,
I need to know how that contamination is creating the effect.
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Tim in Phoenix




Joined: 21 Oct 2006
Posts: 4378
Location: Phoenix


PostLink    Posted: Thu Jun 08, 2017 11:36 pm    Post subject: Reply with quote

Hey CM

A little gassy? or some crud on the cathode maybe. Got a Sencore?
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cmjohnson




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


PostLink    Posted: Fri Jun 09, 2017 12:05 am    Post subject: Reply with quote

No, I don't have a Sencore. I may be able to use one, though.

It doesn't act like a gassy tube. It's very sharp, which is not typical of gassy tubes. But the bloom on shutoff is quite pretty.

The high background noise in it LOOKS like a noisy video amp.

I need to check it out in a Marquee. Maybe do that tonight if I get around to it.
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cmjohnson




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


PostLink    Posted: Fri Jun 09, 2017 3:09 am    Post subject: Reply with quote

I took the time to try this tube out in a Marquee. The issue is the same, absolutely no difference from when this tube was
in a G90. However, after spending a while testing it in several ways, I have reached the conclusion that this is not a problem
that is likely to significantly affect normal viewing. In fact, while watching several scenes from a few movies, I did not notice
any picture quality issues. Not even in dark scenes.

Taking the contrast down really low at some point actually makes the background get BRIGHTER and noisier, but we're talking
about a contrast setting down below 10. At normal viewing levels, this is a non-issue.

The admittedly very pretty fireworks show still shows up on shutdown, but it occurs over a large enough area of the tube, and
is not so bright as to be a concern, so I do not believe it will have any effect on tube life.

But, it's going to be reserved for Marquee usage only. Without a light meter I can't prove it but I believe that the G90 made
this shut-down image artifact brighter and more noticeable.

I'll set this tube up in Marquee hardware and give it the full test. I'm sure I can find something to do with it, it's really a flawless tube in terms of just watching a movie under normal viewing conditions.
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Curt Palme
CRT Tech



Joined: 08 Mar 2006
Posts: 24296
Location: Langley, BC

TV/Projector: All of them!


PostLink    Posted: Fri Jun 09, 2017 4:29 am    Post subject: Reply with quote

It is an issue with planetariums, I had to change a few over the years, where the tiniest flicker on the tube face was visible on the dome..
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cmjohnson




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


PostLink    Posted: Fri Jun 09, 2017 12:50 pm    Post subject: Reply with quote

Fortunately I don't seem to have any planetarium customers. Very Happy
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kal
Forum Administrator



Joined: 06 Mar 2006
Posts: 17850
Location: Ottawa, Canada

TV/Projector: JVC DLA-NZ7


PostLink    Posted: Fri Jun 09, 2017 1:33 pm    Post subject: Reply with quote

If you do sell it, be upfront about the contamination in the electron gun. What may not annoy you during usage may annoy someone else.

Kal

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Curt Palme
CRT Tech



Joined: 08 Mar 2006
Posts: 24296
Location: Langley, BC

TV/Projector: All of them!


PostLink    Posted: Fri Jun 09, 2017 1:38 pm    Post subject: Reply with quote

Yeah, I agree with Kal. Stupid thing is, that contamination can happen overnight. I've sold more than one projector over the years where a short while in (a couple of days to a couple of months) one tube gets contaminated after the customer receives it. No telling when, or if, a tube will do it.
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cmjohnson




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


PostLink    Posted: Fri Jun 09, 2017 1:49 pm    Post subject: Reply with quote

Definitely. No surprises to the buyer, NEVER. I absolutely believe in full disclosure.

I have a video of the tube on shutdown showing the pretty fireworks. I'll post it. But I want to reshoot it because autofocus went nuts on it.
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kal
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Joined: 06 Mar 2006
Posts: 17850
Location: Ottawa, Canada

TV/Projector: JVC DLA-NZ7


PostLink    Posted: Fri Jun 09, 2017 2:19 pm    Post subject: Reply with quote

cmjohnson wrote:
Definitely. No surprises to the buyer, NEVER. I absolutely believe in full disclosure.

Like the 'minty' spot burnt / delaminated tube you sold me? (Sorry, couldn't resist) Wink

Kal

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cmjohnson




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


PostLink    Posted: Fri Jun 09, 2017 2:28 pm    Post subject: Reply with quote

You mean that green 8" tube that I posted clear photos of, which showed a very tiny, barely noticeable WEAR MARK on it, which I know was not a spot burn or delamination, but you never actually bothered to power up the tube and LOOK at it in operation?

The one that was from the Universal Studios, Orlando, "The Mummy" thrill ride, which spent its idle time on the intro screen which showed an Egyptian burial mask like the famous gold and lapis mask of King Tut?

That one?

Yes, I remember it well. You threw a hissy fit over that tube I sold you for 50 dollars. 50 lousy dollars for a tube with one mark
on it that was honestly hard to see without looking for it. Which was sold with photos of the tube face for you to see first. Which you never bothered to hook up and see if the image would even have shown a visible mark on it.

And for which I refunded your 50 dollars and told you to keep the tube or toss it if you want. For all I know you still use it

No, I don't remember that one AT ALL, Kal. Very Happy
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kal
Forum Administrator



Joined: 06 Mar 2006
Posts: 17850
Location: Ottawa, Canada

TV/Projector: JVC DLA-NZ7


PostLink    Posted: Fri Jun 09, 2017 3:28 pm    Post subject: Reply with quote

cmjohnson wrote:
You mean that green 8" tube that I posted clear photos of, which showed a very tiny, barely noticeable WEAR MARK on it, which I know was not a spot burn or delamination

No. It was a green tube. Not to open this up again CJ, but you never posted any photos. Not sure why you're lying about it now. Here's your for-sale thread for you to check yourself: http://www.curtpalme.com/forum/viewtopic.php?t=20780

You wrote:

"1 GREEN P16LNP47HKA, 8" CRT installed in a Barco Cine 8 LC chamber, with green C element. Phosphor condition is pristine. Hours unknown but it can't be much. Envelope glass is only very lightly tanned, indicating low operating hours as well. (It turns brown from X-ray absorption and gets darker as the tube has more hours on it. This is true of all projection CRTs.) Photos available on request. (I haven't made any yet.) "

I never requested photos, you never posted any.

cmjohnson wrote:
...but you never actually bothered to power up the tube and LOOK at it in operation?

Because I'm not a moron. The delamination/spot burn was clearly visible to the naked eye. Anyone who knows anything about tubes knows that if you see it with the naked eye, it's only going to show up 100x worse on screen. Putting it in a projector would have been a futile giant waste of time to prove the obvious.

It makes as much sense as installing a flat tire full of holes on your car to prove that it won't work. If someone sells a flat tire you don't expect them to say "Well did you try driving on it? How do you know it's not going to work if don't install it and drive on it first?".

Some things you don't need to do to prove the obvious.

Quote:
The one that was from the Universal Studios, Orlando, "The Mummy" thrill ride, which spent its idle time on the intro screen which showed an Egyptian burial mask like the famous gold and lapis mask of King Tut?

That one?

Yes, I remember it well. You threw a hissy fit over that tube I sold you for 50 dollars. 50 lousy dollars for a tube with one mark
on it that was honestly hard to see without looking for it. Which was sold with photos of the tube face for you to see first. Which you never bothered to hook up and see if the image would even have shown a visible mark on it.

You're confusing me with someone else. The tube you sold me was $200.

Quote:
And for which I refunded your 50 dollars and told you to keep the tube or toss it if you want. For all I know you still use it

No, I don't remember that one AT ALL, Kal. Very Happy

You don't. See your original for-sale post. The link above.

You're confusing the tube you sold me with someone else you sold a worn/defective tube I guess.

Kal

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Last edited by kal on Fri Jun 09, 2017 4:28 pm; edited 1 time in total
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