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Sony D50 green flash during power off

Discussion in 'Projectors, Screens & Video Processors' started by klr10, Dec 20, 2003.

  1. klr10

    klr10
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    I'm looking for some help fixing a problem on my Sony D50. When powering off the unit there is a brief green flash in the middle of the screen which then fades rapidly outwards, I realise this will eventually burn a mark into the green tube. Luckily I have a scrap projector and with the advice of the guys at CRTcinema.com (who recently sold me a new blue CRT) I have replaced (in turn) the PA and K boards, the E board, the AC board, Main Power Supply and the Green neck board. I've also tried a full factory reset and turned all the gain/bias/contrast/brightness to minimum. I've also gone all over the projector looking for loose wires in the many plugs to these boards. The only other clue I have is that there is still a slight glow on the screen even with all these turned down (ie it's not black black), and you can make out the shape of the glass. Is there something I've missed? Am I doing something silly? Any help would be most appreciated...
     
  2. klr10

    klr10
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    Put the old worn green tube back in - no flashes... Does this mean the replacement green (low hours, out of a wrecker) is bad or is it normal with a low hours green tube. Or is there a G2 adjustment somewhere that I don't know about? I guess if the green tube is causing the problem I have nothing to lose by leaving it in? Anyone know how long it will last like this before a burn becomes apparent?
     
  3. ShinObiWAN

    ShinObiWAN
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    It will likely last just as long as a tube that doesn't have the defect.

    I'm no CRT expect by a mile but I've read many, many posts on the burn in phenomenon and always the conclusion is that it has to be a prolonged and bright image for damage to occur.

    I'll quote Curt from Avsforum:

    "Severe Burn-in would most likely occur if an image is constantly displayed for 24 hours or so and with moderately high contrast and brightness levels. It takes a level of gross negligence to really damage the phospher area."

    So a brief flash when powering off the machine is peanuts in the grand scheme of things.
     
  4. helipilot

    helipilot
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    I would advise getting the problem sorted as soon as possible. This is definately not a problem to be ignored.

    The type of burn-in that Curt is referring to is during normal operation of your projector. In other words the electron beam is constantly scanning across and down the crt surface to make up the image. The danger occurs when the beam stops moving and hits a single spot on the tube surface. The flash you see at shut down is because the electronics have stopped moving the beam across the surface of the crt. Although the beam has stopped moving it is still carrying a tremendous amount of energy. This energy becomes concentrated on the centre of your crt and severely over exites the phosphor causing the flash. There should be a protection circuit that stops this happening. If you continue to see this happening you will burn a hole in the phosphor and end up with a black blob in the middle of your green tube.

    I would suggest when you do shut down to firstly display a full black field on the screen using something like a video essentials dvd. Now switch off the projector followed by your dvd player etc.

    I am not sure if the above will prevent the flash or not (it depends on what the electronics of your projector do on power down) but its got to be worth a try at least once and it just might save your tube.

    If your old green tube does not flash it looks like it could be a fault with the replacement tube. Are you sure it is exactly the same spec tube you have fitted ? Does the newer tube have a pin missing ?
     
  5. ShinObiWAN

    ShinObiWAN
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    Thanks again Heli,

    I'm learning new information about CRT's all the time.

    After reading Heli's advice I'd suggest you ignore my post, klr10.
     
  6. klr10

    klr10
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    Thanks guys, I know how it all works but I'm not familiar with D50s (I am an electonics engineer by trade). I think the replacement tube I used must be bad. I checked the pins against the old one and the readings are the same. I have access to another D50 so I plan to borrow a good green and try it. The only other thing is the scan coils which being a used tube were already fitted - be surprised if it is this though... So if it proves to be the tube I'll need to decide whether to live with it and change the green when it starts to mark or be fussy and change it now (about £400 new inc shipping) Will send updates to this thread when I've tried the other green. Probably do it after Christmas now - getting a bit fed up with removing and replacing tubes!! Thanks guys and Happy Christmas... Keith
     
  7. Roland @ B4

    Roland @ B4
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    Why don't you temporary try the red or blue tube from your scrap unit to see if it is the tube or further up the line.
     
  8. klr10

    klr10
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    Yep, It is the tube. Ordered a new one from crtcinema.com if anyone's got a use for an otherwise perfect D50 green (not burned), then let me know. I can't keep taking the thing on and off the ceiling, rather fix it once and for all....
     

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