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G90s breaking tubes

 
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cmjohnson




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


PostLink    Posted: Thu Nov 09, 2017 1:04 am    Post subject: G90s breaking tubes Reply with quote


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Not long ago I sold a G90 to a guy who just reported today that it broke its green tube, which I'd replaced.

I've seen more G90s break tubes than any other projector.

It's usually the green tube, and I've seen a broken blue as well.

But never a red tube.

The red lasts longest and gets the least wear and tear on it. As it gets the least drive it stands to reason that
it also generates the least heat of the three.

I'm seeing tube breakage that follows the pattern of which tubes are driven the hardest.

I believe the problem is thermal shock and questionable thermal management
of the CRT in the G90's tube assembly design. Specifically, the coupling between
the tube face and the aluminum mounting frame. Those four metal spacer pins, to be exact.

I think they create "cold spots" on the tube face.


But I was also thinking about the presence of the G90's warm-up screen.

I'm wondering if using it, or not using it, has any bearing on tube breakage or avoiding same.


Thoughts, comments, and opinions, please?
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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 Nov 09, 2017 2:40 am    Post subject: Reply with quote

Pretty common occurrence. One client that bought those NOS MArquee LCP tubes that I had, had one implode within 2 hours of firing it up. The replacement worked fine.

I always tell people to turn off the warmup screen, but I believe the client whose tube imploded didn't have it turned on. It died during setup.
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cmjohnson




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


PostLink    Posted: Thu Nov 09, 2017 4:56 am    Post subject: Reply with quote

Curt, have you ever seen this happen with anything but a G90?

I personally have not.

I think that because the G90 is so sharp, people drive the tubes hard because most people stop driving the tubes harder when the picture starts to get soft. Since the picture really doesn't seem to get soft they just crank it and that means hot tubes and that means thermal management failure.

Yeah, guess where my customer had it set? Contrast at 100 on a PC desktop display. He'd turned it up because he had watched
a dark horror movie and forgot to turn the contrast back down when he switched.
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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 Nov 09, 2017 3:02 pm    Post subject: Reply with quote

Yes, on all other sets, E'homes included. the G90 is definitely the most often though. I think it's the sharpness of the beam frankly causing the face to shatter.

Last edited by Curt Palme on Thu Nov 09, 2017 4:03 pm; edited 1 time in total
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HaydnG90




Joined: 22 May 2006
Posts: 1335



PostLink    Posted: Thu Nov 09, 2017 3:36 pm    Post subject: Reply with quote

Maybe its just my cautious disposition but my warm up procedure is to turn the G90 on with no inputs for at least 15 mins. In this way the internal components are slowly brought up to temp before actually driving the tubes. My G90 has about 3500hrs on the chassis and R/B tubes and 3000 on the G. Served me well so far.
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gjaky




Joined: 05 Jun 2010
Posts: 2789
Location: Budapest, Hungary


PostLink    Posted: Thu Nov 09, 2017 4:28 pm    Post subject: Reply with quote

Maybe it's not that relevant, but I remember Tim doing an "experiment" with forcing a tube to turn on at max contrast without deflection coils and LC chamber, it eventually melted the glass to some extent in the middle, but nothing catastrophic happened.
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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
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mp20748




Joined: 12 Sep 2006
Posts: 5681
Location: Maryland

TV/Projector: 9500LC Ultra / Super 02 and 03 VIM


PostLink    Posted: Thu Nov 09, 2017 8:17 pm    Post subject: Reply with quote

Tube breakage was more common on a G90, but extending the beam to the edge of the CRT envelope at high contrast levels on a Marquee would also crack the CRT.
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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 Nov 09, 2017 8:49 pm    Post subject: Reply with quote

Very true!

When the NEC XG V boards would die, they'd send the beam off the edge of the tube face, and for some reason the NEC protection circuits didn't detect this. The electron beam went so far off the tube face, it hit where the neck of the tube hit the bell,and would snap the tube within seconds. Happened once at a client's place, who complained of an intermittent green pix. I saw it happen, but was diagnosing the video circuit when the tube went POP! Not a good day, although it was a very used set, with a very worn green tube. To my defense, that was the first time I saw that problem, and then saw a few repetitions of it over a few years.
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Jeremy112




Joined: 28 Sep 2006
Posts: 2645
Location: Fond du Lac, WI


PostLink    Posted: Fri Nov 10, 2017 9:24 pm    Post subject: Reply with quote

I had a green tube crack on my XG1100 from too much pressure in the coolant chamber. I never checked it when I got it, so it was my own fault, but yeah I've seen it happen, freaks you out! When the tube imploded the phosphor face itself cracked and the glycol went into the bell and neck, the projector was still running after it happened, so I pulled the power cord out of it right away. I threw a new tube in and it was like it never happened.

I think between pressure, fast changing temperatures, and even how its being used right after power on all play a role as far as tube reliability goes. I don't think it's specific to any projector, just how they get used and maintained. Smile

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