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black is grey(ish)

Discussion in 'Projectors, Screens & Video Processors' started by dprior, May 4, 2003.

  1. dprior

    dprior
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    As time is passing and I'm getting familiar with a CRT picture I am now bothered by the blacks being rather grey. I have done some searching and the term 'G2s' comes up a few times.

    The general thinking seems to be: choose an unconnected input (or black screen from a film), turn the contrast and brightness to mid position and look into the lenses. The raster should not be visible.

    When I follow the steps above the raster is glowing rather a lot, even when the brightness and contrast are further adjusted all the way to zero.

    If my deductions are correct it seems like the g2 voltages are set to high and are robbing me of nice deep blacks.

    If this is correct could someone please tell me how to adjust the G2 settings for the tubes.

    I tried to search for G2 but it is under the limit of 3 characters!!

    The PJ is a Sony 1271

    Thanks

    Darren
     
  2. Chris Frost

    Chris Frost
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    Maybe stating the obvious, but before you dive in to G2 settings make sure you have the picture controls set correctly. May also be worthwhile checking the Bias & Gain settings.

    Use the AVIA test disc (search for AVIA on any internet retailers site for more info) as a good source of test patterns for these fundamental adjustments.

    Regards
     
  3. nathan_silly

    nathan_silly
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    You need to setup the picture with something playing, as the format type (PAL/NTSC) and refresh have individual settings on PJ, plus geometry & convergence settings.

    CRT black is very good. Sounds like you've got brightness set too high.

    Avia is good but NTSC only. Video Essentials is PAL. Or you could use a laptop S-Video output set to PAL with a few test screens (I have created my own grids to check PAL) - also got Avia as well as primary DVD watching is DVD so I want NTSC as good as possible.
     
  4. dprior

    dprior
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    Thanks for the replies.

    I have tried adjusting bias and gain settings with and without something 'playing' and still the rasters do not dissapear. They are always glowing.
    Adjusting brightness and contrast also never reduces the glowing rasters.

    Chris, which 'picture settings' are you refering to?

    My source for the pj is a htpc via 5 BNC, the picture is great except for the black levels.
    The reason I think it may be the G2 levels is because: 1) I have the same lines as 'meep' described in a recent thread whhich Roland described a 'fly back' lines caused be G2s being too high and 2) from a setup thread on avsforum explaining setting up G2 levels.

    Could someone please tell me how I can change the G2 levels, even if just for future reference.

    Thanks

    Darren
     
  5. Chris Frost

    Chris Frost
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    Darren, The picture controls would be Brightness, Contrast, Hue, Colour, etc.

    If you can see the raster and the flyback lines then your diagnosis of G2 levels may well be correct. I'm not a Sony expert (Gordon is the man for that) but I am curious how the G2s got so out-of-whack in the first place.

    Good luck

    Nathan,
    Unless another edition of Video Essentials has been released I think you'll find that VE is NTSC. Both AVIA and VE are Region 0 though so will play on any unmodified DVD player world wide.
     
  6. gizlaroc

    gizlaroc
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    Do youself a favour and nip down to maplins and get one of their £4.99 multimeters.

    Adjust your G2 settings to 4v.

    you will be suprised at how much difference this makes to your overall pic quality.
    the CFB-5 board is under the main board and easy to get to.

    [​IMG]


    you just stick the negative probe in between pin 1 and the platic surround (will stay in place) and then the positive on pin 2, 3 and 4 for B, G and RED.

    I bet you are overdriving them by at least 50% , I was, and I thought I had it spot on :blush:
     
  7. dprior

    dprior
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    Thanks again for the relpies,

    I discovered that the G2 pots are next to the focus pots!!!.:D

    I paused a dvd on a black scene and 'slowly' adjusted the setting until the raster just disappeared.

    Chris, you were right about the settings! just by altering the brightness from ~40 to ~50 made the raster glow in the areas that should be black, this however was only on the red tube. The green and blue were constantly glowing even with brightness at zero. I didn't realise that upping the brightness by just 5 points on the scale would affect the raster so much.

    I just need to wait until it gets dark to test the settings out. (The other half has been supportive and completed one blackout curtain, but there is one left to go).

    Gizlaroc, if the picture proves to be much better i may measure the voltages just to see. I have a multi-meter lying around somewhere. It will be interesting to see if its near 4V

    Thanks again for all the advice.

    Darren
     
  8. gizlaroc

    gizlaroc
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    Best to set the brightness and contrast to 0 if you are setting the G2 by eye.


    A nice little set up tip from Roland below-
    find a black bit if a dvd, pause it then with the levels set at zero adjust the G2 pots until you can just, and I mean just, make out the glow of the raster.
    make sure they are all the same intensity too.

    I thought I had the settings spot on until I was reading a post on the avsforum, somone asked "how black is black?" and one of the guys on there asked him whether he could see a shadow if he held his hand up in front of the screen with a black image.

    I tried this and there was an obvious shadow, got the multimeter out and my G2 were over 6 volts.
     
  9. dprior

    dprior
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    I set the G2s to just see the raster glowing and the dark scenes are seem a lot darker now. I don't think I had the settings quite a zero when setting them, but the values were low. I will try adjusting again with the levels set to zero first. I guess that the rule of letting the PJ warm up is probably advisable also??

    I few tweeks to come i think, but its already a good improvement and definately not so washed out looking.

    I still may try to measure the voltages but I don't want to poke about too much. There are some high voltages in there!!!

    The next step is the bias and gain. I can see the effect each has but what are the methods used for setting these properly. When the bais or gain buttons are pressed I'm not totally sure what the images on the screen are trying to tell me. (plunge screen for example). The gain brings up the white square but 'white' can be achieved with the settings low or at max settings. How do you now where to set them???


    Any advice would again be much appriciated. The picture is looking good but maybe it can be improved again.

    Darren
     
  10. gizlaroc

    gizlaroc
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    If your g2 levels are set correctly you shouldn't have to adjust the bias and gain settings, reset them to factory defaults and see if your whites look white and the grey looks grey.

    I had to knock my green gain down 2 notches after I had set the G2 levels, and that was all i have adjusted.
    I know that to get a proper greyscale I would need someone like Gordon to calibrate it properly , but I am going to get that done when I move up to a better PJ.
     
  11. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    There are pics on my web site I think about how to set G2 on one of these. Use the voltmeter it's not hard and it'll stop you trashing the thing.

    You will probably have to adjust bias and gain for greyscale, especially now that you've played with G2 and electical focus. Good luck.
     
  12. Roland @ B4

    Roland @ B4
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    All pretty good advice so far and so not a lot I can add

    Just a word of warning their is 34,000 volts just the other side of these contols. no metal screwdivers or wet fingers.

    In most case only the tinest tweek is required.
     
  13. gizlaroc

    gizlaroc
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    Oh but how those voltages jump around as you turn the pots, one of the most frustraing 20 mins i have ever spent, but once I had it all open and the meter out I was going to make sure that they were 4.000 volts exactly :D
     
  14. dprior

    dprior
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    I will have to wait for a chance to get inside the PJ to check voltages.

    Gordon, I could not find anything on your site about setting G2. Any chance you could post the direct link to the page on this thread if I did miss it.

    Thanks all, I'll post my findings when i've had time to adjust and measure. Your help has been invaluable.

    Cheers

    Darren
     
  15. dprior

    dprior
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    One more Q.

    Gizlaroc/Roland: refering to the comment "tip from Roland"

    with the levels set at zero... Does that mean at there lowest possible setting or at midpoint??

    The Sony reads 0 to 255 with midpoint at 128 (i think) , but some may go positive to negative.

    THANKS

    Darren
     
  16. gizlaroc

    gizlaroc
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    sorry i meant the contrast and the brightness both set to zero.
     
  17. Roland @ B4

    Roland @ B4
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    The need to be set to their minimum to prevent the projector amplifiing the black signal.
    In theory just the brightness should do this, but often manufactures made small adjustments to the brightness whilst you adgust the contrast.

    the G2 voltage which is what you are setting controlls the speed and number or electors that are drawn into the CRT to make the phosphor glow. Incorrect setting can wear out a tube or withwold its true performance.
    In a home cinema environment brand new tubes might need adjusting after a 1000 hrs. Used (ie over 1000) probably every 2000.

    I recon that for most of us that about once every 18months to two years!
     

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