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Discussion Starter · #1 ·
I have come to observe that when my G70 shuts off, there appears to be a small green "exploding" dot right at midscreen as the last visible light on the screen. Is this normal? Why does it happen?
 

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The circuitry that normally blanks the electron beam when you shut off the unit is failing. What you're seeing is the beam collapsing to the middle.


Think Grandma's old TV where you used to see a line collapse to a dot when she turned off the TV...


If it gets bad enough you can easily (and instantaneously) burn a spot in the middle of the tube because of the intensity.


Kal
 

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Discussion Starter · #8 ·
Thanks for all the replies.


1. It is not of high intensity. Only barely visible if all the light is off in the room when the PJ shuts down.


2. Is there a fix? What is it?


3. Know a service man in Atlanta?
 

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2. Is there a fix? What is it?


Since the 'exploding dot' is green, like Mark mentioned above, I'm guessing that's it a problem with a the green neck board. I've never worked inside a Sony G70, but I'm assuming that you could swap the green neckboard with red see if the problem moves to the other tube (ie: The colour of the dot changes to red). Make sure the neckboards are actually swappable before attempting of course - sometimes there's subtle differences in one

of the them on some PJ's.


If the problem moves to red, you need to get the neckboard replaced/fixed before the problem gets worse.


If the dot is only very slightly visible now then there's probably no harm done to the green tube, but since there IS a problem, you never know - the problem could get much worse all of sudden and give an intense flash once during shutdown causing permanent burn to the green.


One option (for now) would be to mute/blank the tubes before turning off the unit until you fix the problem. Collapsing a black image to the center of the screen doesn't cause a bright flash since there's no image content. In fact you could use this method forever really if your spot suppression has completely failed. Problem is that one day you'll forget to mute/blank the image and then you run a high risk of damaging the green.

3. Know a service man in Atlanta?


I would first confirm that it's ok and then swap the green with the red neckboards - if the problem moves over you know it's the green neckboard in which case you can send it out to any one of the techs here on the board - it doesn't have to be someone local.


Kal
 

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Discussion Starter · #10 ·
Thanks for your reply. As I stated, the problem seemed to be of low intensity. However, as my son was in the theater when I read the original replies and sent my second questions, I went down there and was in there when we shut down, and no Dot at all. Could not replicate it. So what do I make of that? Could it have to do with which input I was using, and the system shutdown order I had programmed into my Pronto?


Neck boards are outta my league. Will need help on that one.
 

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Quote:
Originally posted by MS
Thanks for your reply. As I stated, the problem seemed to be of low intensity. However, as my son was in the theater when I read the original replies and sent my second questions, I went down there and was in there when we shut down, and no Dot at all. Could not replicate it. So what do I make of that? Could it have to do with which input I was using, and the system shutdown order I had programmed into my Pronto?
Shouldn't have anything to do with the input you were using. Beam spot suppression is beam spot suppression... it has to do with blanking the beam before the horiz & vert deflection collapses. Completely independent of what input you're using.


It could certainly be the system shutdown order if you shutdown the source you were on first which caused a black screen to be shown by the projector. If you shutdown the projector while it's showing a black (blank) screen, you shouldn't see much (or any) dot in the middle since there's no image content to collapse to the center.


Try it again a few times. I doubt something like this would just "go away" by itself. It will most likely get worse over time.


Kal
 

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Well, I've actually had two BArco 808's recently that did exactly the same thing. Low intensity dot in the middle of one tube at shutdown.


I changed EVERY board in both 808's, and it did not cure it, so I'm suspecting the tube itself. I'm guessing the tube cutoff shifted slightly. The dot is so weak that there's no way it will burn the tube, so it will be fine. I'll bet the Sony is doing the same thing, so other than changing the CRT board to another tube to make sure it's not the board I'd probably leave it alone.


Other than that the sets looks perfect.


Thanks!

Curt
 

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Quote:
Originally posted by Curt Palme
Well, I've actually had two BArco 808's recently that did exactly the same thing. Low intensity dot in the middle of one tube at shutdown.


I changed EVERY board in both 808's, and it did not cure it, so I'm suspecting the tube itself. I'm guessing the tube cutoff shifted slightly. The dot is so weak that there's no way it will burn the tube, so it will be fine. I'll bet the Sony is doing the same thing, so other than changing the CRT board to another tube to make sure it's not the board I'd probably leave it alone.


Other than that the sets looks perfect.


Thanks!

Curt
Did you try replacing the SMPS as well Curt when you did the board swapping?


Reason I ask is that in the 800's SMPS, there's a 17VDC source that needs to be at 17VDC or slightler higher - if it sags even just slightly below 17, you get the center dot at shutdown. Not super-bright or long lasting by any means, but still there.


I'd imagine that the 808 has something similar.


But then again, I imagine you already knew all this! :)


Kal
 

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Yes I swapped everything, and even tried the boards in the 'bad' set in a working one, which worked fine as well. Everything points back to the actual tube.



I'll sell it to an honorable buyer in Indonesia who pays by Mastercard, do you aggree?


;)


Curt



Curt
 
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