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Bert Randolph
Joined: 03 Jul 2007
Posts: 81
Location: Germany
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| Posted: Thu Aug 07, 2008 10:52 pm Post subject: NEC XG: Spot Burning my tube? |
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Today I swapped in a new system board in my XG 1351 LC. Everything went fine, until I noticed that, when I shut the unit down, the red tube seems to loose its deflection: A line in the middle of the tube, followed by a tiny spot.
I got worried and switched back to the old system board. Nothing changes, same behavior on red.
The intensity of the beam does not seem to be very bright - I think my mouse pointer is brighter when the set is on.
But i really don't want to ruin this now.
Any suggestions? Is this normal or not?
I have made two videos: One showing the shutdown (SHUTDOWN.AVI), one showing the mouse pointer for brightness reference (MOUSE.AVI).
See them here:
http://www.physik3.gwdg.de/~dschanz/XG/
Thank you guys,
Daniel.
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Thu Aug 07, 2008 11:07 pm Post subject: |
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Check the red G2 lead on each end, at the tube socket and on the HV board. Make sure it's not unplugged. That is NOT normal for an XG...
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jkruger
Joined: 24 Oct 2007
Posts: 2435
Location: Carlsbad, CA
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| Posted: Thu Aug 07, 2008 11:49 pm Post subject: |
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Could that be an internal tube short? Some crud on an element causing a line/spot on shutdown? My blue tube has done a similar thing intermittently for more than a month now. Supposedly that can be burned off with a Sencore?
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Fri Aug 08, 2008 12:52 am Post subject: |
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I've never seen that happen on an NEC type of tube, only the MEC ones used in the Marquees/Barcos. Different electron gun structure maybe?
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jkruger
Joined: 24 Oct 2007
Posts: 2435
Location: Carlsbad, CA
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| Posted: Fri Aug 08, 2008 1:10 am Post subject: |
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Ah... good point, you would know. I'm a newbie so I was just tossing out what I had seen on my Barco.
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Bert Randolph
Joined: 03 Jul 2007
Posts: 81
Location: Germany
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| Posted: Fri Aug 08, 2008 7:36 am Post subject: |
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I checked the G2 lead and there was nothing wrong: tight and firm, where it belongs.
I remember I had to turn down the brightness of red (BLK in KELVIN menue) to very low values (I think about 17/100)
to have good blacks on red. Might this have something to do with the G2 beeing off? (just guessing now)
I am afraid to turn the thing on to do some testing.
Curt, do you think a spot burn can develop from some power on/power off cycles from what you are seeing on the videos?
I know, not easy to answer and no guarantees 
Is it possible that the new system board fried something? The software-values were all zeroed, are there any other settings that can endanger the machine?
Thanks,
Daniel.
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dbaisey
Joined: 09 Mar 2006
Posts: 821
Location: Southern Cal LA / Seattle WA
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| Posted: Fri Aug 08, 2008 6:28 pm Post subject: |
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Daniel,
You should take a look at your old ref white balance settings for each color. Drive control, bright bias, bright gain, and black bias (G2) then compare to the new board. This is in addition to the W/B settings for each color. This might point to what is going on with the red.
I doubt the system board would be jacked up enough but just be sure.
XG's dont have spot kill issues at all. Bummer but at least it was the red and not the green. Doug
Check to see if the HV board has sealed protect 1-2 pots or if they are unsealed. Might also do a visual on the back of the neck board for a heated surface mount resistor or if one is blown off.
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Bert Randolph
Joined: 03 Jul 2007
Posts: 81
Location: Germany
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| Posted: Fri Aug 08, 2008 11:29 pm Post subject: |
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Doug, I noted all the values. Will compare, when I put the new board back in.
I checked: until now no spot burn is visible.
It is still losing deflection when i shut down, though it is really very faint.
But may this be dependent on what is on screen when I turn off?
At the moment i always have a black screen when switching off, so only the energy of the dim raster will concentrate in the middle spot. When I have a bright image - say a windows explorer - when i shut the unit down - would this come result in a lot more energy in the collapsing beam, then causing spot burn?
| Quote: | | Check to see if the HV board has sealed protect 1-2 pots or if they are unsealed. Might also do a visual on the back of the neck board for a heated surface mount resistor or if one is blown off. |
If the protect 1-2 pots are these black things with silicone coming out of all holes I guess they are sealed. Will check the neckboards later
Thanks,
Daniel.
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Fri Aug 08, 2008 11:55 pm Post subject: |
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| dbaisey wrote: |
XG's dont have spot kill issues at all.
Check to see if the HV board has sealed protect 1-2 pots or if they are unsealed. Might also do a visual on the back of the neck board for a heated surface mount resistor or if one is blown off. |
I agree, never seen an XG with a spot kill problem. In the off chance that it's the neck board, put the green on the red tube, DO NOT put the red tube one on the green, and see if the problem is still there.
I've never run the white balance values at close to 100 before, that _might_ account for spot burn, but I really doubt it.
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Bert Randolph
Joined: 03 Jul 2007
Posts: 81
Location: Germany
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| Posted: Fri Sep 12, 2008 11:52 am Post subject: |
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Just an update:
I have used the projector for some weeks now. It still shows the same behaviour on shutdown, but that does not seem to harm the tube, as the beam is really low energy. Seems to be okay!
The best part is that my new system board works fine! No more 'Unregistered Signal' - warnings !
Daniel.
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AnalogRocks
Forum Moderator
Joined: 08 Mar 2006
Posts: 26706
Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
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| Posted: Fri Sep 12, 2008 10:44 pm Post subject: |
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| Curt Palme wrote: | | dbaisey wrote: |
XG's dont have spot kill issues at all.
Check to see if the HV board has sealed protect 1-2 pots or if they are unsealed. Might also do a visual on the back of the neck board for a heated surface mount resistor or if one is blown off. |
I agree, never seen an XG with a spot kill problem. In the off chance that it's the neck board, put the green on the red tube, DO NOT put the red tube one on the green, and see if the problem is still there.
I've never run the white balance values at close to 100 before, that _might_ account for spot burn, but I really doubt it. |
One of the members here had an XG with spot gurn on it. Not sure how it happend though.
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