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Discussion Starter · #1 ·
The BD808 lacks a horizontal linearity control. I'm running into horizontal linearity problems.


Completely clean install, I've deleted all blocks and set everything to midposition. I recentered the rasters, etc...


When looking at just the green gun with an external 16:9 test pattern, the image is too large vertically, a little to narrow horizontally, and appears to be properly centered on screen.


Compressing the image vertically by decreasing v-size causes v-linearity to get screwed up, v-linearity control works to correct the problem.


Widening the image horizontally to fill the screen causes the h-linearity to get screwed up: the right side widens, but the left stays the same width as before. Additionally, the centerline now drifts to the left, forcing me to move the image to the right (using either h-phase or raster shift) to make it line up with the screen; but this causes the image to now no longer fit the screen in any way.



Right now the only thing I can think of is just not use the h-size control and move the projector further back to get proper width. I'm sort of worried about that, as I may run out of v-size adjustment range before I get proper width to fit a 16:9 screen.



Is it possible that my lenses are somehow not fully mounted on the tube faces and this is causing the linearity problem? I seriously doubt that its the case, but its something I've changed recently (taken the lenses off and remounted them).
 

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Discussion Starter · #2 ·
BTW, I've been using this machine for a year without any issues (in 16:9 config). I just moved and am trying to get setup again, only this time I'm somehow being a moron and can't quite get it right...
 

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spearce,


Assuming you're still in a front/table configuration, the two horizontal linearity controls on the horizontal deflection board seem to actually only really help with the left side of the picture. I think every 808 I've ever worked on had the left side linearity out of whack. There is a ferrite core you adjust for standard frequency linearity, and a POT you adjust at a second higher frequency.


The adjustment is very easy to do if you have extension boards, but otherwise it would be a bear. You probably should do the ferrite core and it will likely fix your issue with just that. The core only has a 360 degree rotation that will freely turn in circles with no stops. I think there are two big yellow taped cores on the board, and the adjustment is on the smaller one closer to the back side of the large heat sink. The drive hole in the core is square.


Of course a plastic non-ferrous tool is required for the adjustment. If you could fashion a square plastic drive and then attach something perpendicular to it to turn it with? I guess you could also pull the board, make an incremental move, put the board back in, etc....


Mark
 

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Discussion Starter · #4 ·
Thanks for saying I'm not crazy. :)


I'll take a look at my 808 tomorrow and see if I can reach the core you are describing. I've got some all plastic tools, I might be able to do something with them to turn the core; just to save myself the hours of pull, change, reinsert, powerup, test, shutdown, pull... :)
 

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Discussion Starter · #5 ·
Mark now that I think about it, if that core just turns 360 and doesn't have a very good stop on it, I might have lucked out in the old place in that it just happened to be reasonably set (or I was an idiot and never noticed it before now). When I moved, perhaps it jogged around a tad.
 

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That's possible. The core barely has pressure on its side from a piece of plastic I think and the core's cross-section is slightly egg-shapped (or non-round). Might have moved towards a position of natural tendency.


Mark
 

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Discussion Starter · #7 ·
Major bummer, I found the ferrite core, but I can't locate a plastic tool to make it rotate, the core's drive hole is larger than any tool that I have around, not to mention that it's going to be difficult to craft something that can rotate that core while the card is installed. *sigh*


Thanks for the help Mark, I'll have to see what I can come up with to adjust this core and have a go with it, perhaps this weekend.
 

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hi spearce,


take a wodden rod with a small diameter and sharpen it.

this will work.


-g.
 

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Discussion Starter · #9 ·
:)


Except the stupid hole is square. And I don't have a small wooden rod with a small diameter handy.


I had just picked up some of those $9.99 short focus binoculars at Target the other day. Turns out the plastic they come in is pretty strong, and when sliced down was enough to turn the ferrite. Problem is I can't do it while the card is installed in the machine, so I'll have to pull, change, test. *sigh*


But what fun would it be if I had a proper set of extender cards for my machine? :)
 
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