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Discussion Starter · #1 ·
I'm getting frustrated with my Barco G801. I cannot get it to hold convergence. I always let it warm up for at least an hour using the solid white field from the Nokia monitor test program, but to no avail; the convergence has to be tweaked before every use. Does anyone have an idea as to why this is happening? I love the picture quality of the CRT, but if I have to keep this up there may be a bulb pj in my future (I hope none of my local HT friends read this, I give them crap about their inferior bulb pjs).
 

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Jon,

Tell us about the drift. Is it a bit, is it a lot? Is it raster shift, is it one color or all?? Did you mount your PJ closer than you are supposed to or where Barco Lens called for it??

Terry
 

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I've never noticed the green raster shift, but the blue does occasionally, as does the red, but less often than the blue. The shift is small, no more than 0.25", but enough to make actors' faces have a blue outline on one side and red outline on the other. The blue raster only seems to shift right while the red raster seems to shift up and sometimes left. What is more common is that the zone convergence drifts. I'd say 75% of the time I have move one zone to the right of center and shift the blue back to toward center. With the red, it's the opposite, I have to move to the left of center and shift the red back. The corners are almost always off, with the lower left and lower right being the worst.


I thought at first that this was a temperature related problem, but the CRT is upstairs where the room temperature is fairly constant, and I've let it warm up for as much as two hours to see if that helped, but it didn't.
 

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I just noticed something similar with my BG800. I am STILL in the process of setting it up and last night I decided to take a break and watch a movie since the picture is VERY close to perfect. About 1 hour into the movie the picture suddenly lost convergence on the red CRT in the lower portion of the screen.


I have also noticed on occasion that when I power on the projector once in a great while the convergence is all screwy. Or maybe it is a raster shift, I don't know. If this happens I power off the projector, wait about 2 - 3 minutes and when I turn it back on everything is fine.


If you find what is up with yours post back here as maybe the same thing is happening to mine. I will do likewise.
 

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I think the first thing you need to check is your mechanical setup. If you search these forums, you will note that the experts all harp on and on about how important mechanical setup is.


From my own personal experience so far, this is the most important advice to date, for minimising convergence drift (and everything else for that matter)!


First, make sure you have the PJ mechanically centered and squared / aligned to the screen at the correct distance / vertical screen offset, then make sure you have your rasters mechanically centered and mechanically skew aligned on the tube face (with all electronic controls centered), then make sure you have your red / blue tube / lense angles mechanically aligned for best physical screen convergence, and finally make sure you have your lens flapping ("scheimpflug") mechanically aligned for correct edge to edge / corner to corner focus (with the lense angles of course still set correctly for best mechanical convergence).


Then, when you have done all that, go back and do it all again, before you consider going anywhere near the electronic convergence!


Convergence drift is mostly a function of the temperature coeficients of the various electronic components, so if for example you are using twice as much electronic adjustment on the red deflection drive circuitry than what you are using on the similar blue deflection drive circuitry, you can expect the temperature drift to vary between the two.


With good mechanical setup and convergence, you should only need the minimal possible variance from center in your electronic adjustments.


One possible way of verifying this on your setup, is to carefully measure the amount and direction of drift in each color between cool and warm operating temperatures. You could then try centering all of you electronic controls (everything will probably be out of convergence when you do this), and then do the same drift measurements. Then compare the results. If you find that you have less drift with all of your controls centered (as would be expected), then this confirms you need to pay more attention to your mechanical setup.


Of course, I might be way off track in your particular case, but never the less, another reminder about mechanical setup is good food for thought especially where convergence drift is concerned! ;)


Greg
 

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It's not uncommon for an older barco 800 to require a quick 1 or 2 clicks of red/blue raster shift ever time you use the thing...


Raster shift is when the ENTIRE grid is slightly off from the reference (green). You access raster shift by doing zone convergence on the very middle zone.


My 23000 hour circa 1990 BG800 would usually require this sort of shift every time I used it even when it had been warmed up for an hour. It only takes 30 seconds but really started to annoy me, so I went through the entire unit about 5 months ago and replaced about 50-60 questionable electrolytic capacitors (roughly $100). I also replaced all of the low-voltage caps in the SMPS without bothering to measure them first. The end result is convergence that always comes back to the exact same spot after a 20-30 minute warmup.


Note: Using Nokia's all white test pattern for warm-up for 1 hour is way overkill. You're wearing your tubes for nothing. Use something darker.


Kal
 
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