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Discussion Starter · #1 ·
Hi All,

Need some technical help. I have seen people post this question before

but have never seen a good answer. A while back I bought a used Barco

1208 from a guy on this forum. It had a broken blue tube so I got it

for a good price, bought a new tube and replaced it. It fired up ok and

since I didn't have any place to project it to do any real tweaking I

put it aside until I finish building my house. Now I have the projector

hung and have one problem. The horizontal linearity on two of the tubes

is good but on one it is very bad. The vertical lines of one side of the

grid pattern are close together and towards the center and the other side

is widely spaced and further from the center. By pushing the switch for

that tube on the deflection board for setting whether it is table or

ceiling mount the non-linear problem switches sides, so it is not the tube

but in the drive electronics. On that same deflection board their are

raster width coils (already set) and cables connected to each of the

deflection yokes. Since the cables are the same I swapped two but problem

did not move from the problem tube to it is not in that horizontal drive

electronics. There is another smaller set of wires that go to the

deflection yoke but I haven't traced to which circuit they go, so they

are a possibility or the deflection yoke windings might be damaged by

the old broken tube neck. I will have to dismantle the projector again

to check that out. There isn't much else on that tube but magnetic focus

coil, which I don't suspect, and the stigmators which I have played with

and they are functioning correctly for dot focus and line flair. If anyone

has had this problem and/or knows where I should start looking please let

me know. I have a friend with the same projector so I may try swapping some of the my boards into his projector one at a time to verify that they are good. I will narrow this problem down and let you know the reason for the non-linearity if someone else doesn't have the fix first.

TIA.
 

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Common Barco problem, as there are no horiz linearity adjustments for the 3 tubes, just one universal adjustment.


So,


(1) Make sure your install is 100% perfect mechanically (perp. to screen, proper toe-in of the red & blue tubes).

(2) Use the horiz. width coils on the side of the unit to get as close as possible to correctly ligning up the grids horizontally. To the eye, you may not get that close but every little bit helps. MAKE SURE TO USE A PLASTIC SCREWDRIVER WHEN ADJUSTING THESE OR YOU WILL FRY THE COILS!

(3) Use zone convergence to adjust out the imperfections. Adjutsments made close to the center of the screen will have a greater effect on the grid farther out (in the same direction) so you may be surprised how much you can 'tweak out' these problems with convergence. That being said, try to limit your convergence use as much as possible - the less you use it, the less the unit will drift. If your zones are all between 30-70 on the 0-100 scane then you're doing great. Don't worry if 1 or 2 zones are outside this zone or even fairly high or low. (On my BG800, no matter how I tried, the middle leftmost zone for blue is at around 5 out of 100).


Note: Before starting, make sure to RESET all of your adjustments to the mid-point (50) by using the reset feature in the service menu.


Kal
 

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Discussion Starter · #3 ·
Hi Kal,

Thanks for the reply.

There are individual raster widths but not linearity (just one global).

1. The projector is set up square in 3-axis. Due to non-linearity on the

one tube it just barely lines up the cross hairs.

2. You should use the raster width coils to line up the raster widths

not the grids. You would be pushing the raster into the forbidden

zone if you do it that way and you really shouldn't have to.

3. Before I started I went to the service menu and set all everything

to midpoint. Then I adjusted the optical focus, G2 cutoff, then raster

centering, then raster width, then magnetic focus, then 2-pole

stigmators, then 4 pole, then round and round until as close to perfect

as possible. Finally did geometry on green, then started converging.

The red converged to the green no problem not having to change the

numbers that much. The blues one side with the tight grid could be

pushed out but the far edge it close just as you run out of adjustment.

This is not acceptable to me to be at 0 or 100, you shouldn't have to

do that, need to fix the primary problem.

I was just hoping someone had root caused the problem and could make

the job easy for me. :) Oh well, I'll start 'playing' tonight and see where

it goes.
 

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Hi Kal,

There are individual raster widths but not linearity (just one global).



oops - my typo. Meant to say 'linearity' instead of 'width'. I corrected my post above.

1. The projector is set up square in 3-axis. Due to non-linearity on the

one tube it just barely lines up the cross hairs.



The cross hairs just barely line up? That's odd. With the rasters more or less all centered, the cross hairs should line up in approximately the middle of the tube lens swing (left to right).


What about the horz position pots on the horiz shift board? Maybe the one for blue is cranked right over to one side? (On my BG800, these are brass multi-turn pots).

2. You should use the raster width coils to line up the raster widths

not the grids. You would be pushing the raster into the forbidden

zone if you do it that way and you really shouldn't have to.



Yes, you're supposed to line up the raster widths with these, but in all honesty, Barco horiz linearity problems are something that many people come across and tweaking the raster widths (even just slightly sometimes) can help.


Good luck!



Kal
 

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Discussion Starter · #5 ·
Hi Kal,

Thanks again, good comments. I think the cross hairs on the blue gun

are so far off because if the linearity problem. I have been walking through the service manual looking for answers. The manual has great schematics and circuit description but no troubleshoot comments and some specs are not there such as Deflection coil resistance. I got to thinking if one side horizontal deflection coil is out of spec it would do strange things. Having three of many things, R-G-B, is handy, I measured the resistance of the deflection coils, all verticals measure the same at about 5 ohms, the individual horizontal coils, right and left, each measure about .45 ohms except one side of the blue guns coil, one is at 3.5 ohms so this may be the problem or at least part of it. To find out I will have to dismantle two guns and swap deflection yokes. If the problem follows the yoke 100% then it will be new yoke time. I'll let you know how it goes as soon as I can get the time to do that. Right now I have to get ready for a plumbing and electric inspection on the house. :)

BTW, I know many Barco's share the same circuits so if anybody needs help just email me and I'll look up info for you, worst case I could scan and

email a .jpg. Also, this is my first projector but I have rebuild TVs before, new tubes, align the IF and converge the picture. These projectors are very nice toys! John
 

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Discussion Starter · #6 ·
Forgot to respond to the raster shift pots question. After setting the mid-point to 50 on the raster shift I checked that the shift pots were near mid-range then used them to shift the raster to center. Most things on this projector are close enough to mid-point to make me happy, just this one bug to fix.
 

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Hello John


You can try to pull out the convergence board in the front of the projector and power it up without it

If the problem is gone it's on the convergence board

Which color was the problem


Rob
 

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Discussion Starter · #9 ·
Hi Rob,

Yes the problem is with blue. Without the convergence board I get the same problem as when the convergence board is in. I am about to swap the deflection yokes, blue and green to see what happens. I'm not 100% convinced that is the problem since the problem changes side when the ceiling/table switch is switched, if it was the yoke it seems like it should stay on the same side. Which leaves a few other possibilities. When you switch the inversion switch it swaps HDL-B (horizontal deflection low- blue) and HDH-B so the problem may be further back in the deflection drive. And, I'll keep you informedas to what I find out.
 

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Discussion Starter · #10 ·
Ok, I have pulled the projector apart enough to slip the yoke off (this would have been easier to do on the table rather than hanging from the ceiling :) ). The windings on one side are quite damaged, don't know how I missed that on assembly except that I wasn't looking for it. So does anyone know where I can get the deflection yoke for a Barco 1208/2 P/N R9000898 if I read this label right.

Thanks,
 
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