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Discussion Starter #1
Hi everyone,


I'm sorry to post another ecp / G2 question but I've been trying to set up the video alignment on my ECP 4501 using the instructions in Section 4.7 of the service manual and I'm having some problems getting things quite right.


I assume that this is occurring because I'm not using the RGB generator set (as suggested in the instructions) for 1 volt peak to peak. I have access to an Extron VTG-150 RGB generator which includes scan rates for VGA, VESA, XGA and MAC rates as well as some CAD workstation rates (includes SGI / NeXT/ Sun/ DEC). The RGB output (BNC Analog) is r/g/b at 0.7v p-p with h & v sync at TTL levels


My first question might sound a bit silly but ..... where do I get an output test signal which gives 1v p-p ? ........ should I be using one of the CAD rates on the computer outputs ?


If I use the rgb analog (BNC) outputs on the VTG-150 to provide a white field and greyscale pattern and follow the instructions in the service manual, I can get a pretty good picture. OK, I can't afford a proper ISF calibration right now (not too many people in the UK to do it anyway) but I was pretty happy with the overall result (it took me a number of goes to get it right).


My problem is ...... when I play* something that is pretty dark (e.g. space scenes in the Star Trek : The Motion Picture dvd) I'm seeing one half of the screen lighter than the other. In previous discussions of this subject, the response has been to reduce the G2 pots a little. If I do that, I lose detail at the black end of the greyscale.


Is this all due to not using the correct levels on the rgb generator ?

or

Am I doing something wrong in setting the G2 or drive levels ? (steps g and i in the procedure)

or

Am I not setting R8 correctly in the first place ?


(* I'm using the VGA (rgb+combined sync) output from a Skyworth dvd player for playback. The output voltage from the Skyworth player does seem a little on the low side so I was having to lift the contrast and brightness controls on the projector a little.)


Many Thanks,


Brian.
 

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Hi Brian, I had the exact same problem with my ECP3101. Turning down the G2 fixed it of course but I lost information in the dark areas of the image. I couldn't live with that.


I was able to fix this but you won't like it - I had to mod the Video Control Module.


Some people have called this "feature" of the ECP units an internal pluge pattern. I don't go for that. If you've got an oscilliscope, schematics, and are willing to probe around the Video Output boards on the CRT end, you'll see that the bright field is caused by the video clamping circuit actually *raising* the video level above black during horizontal retrace. Turning down G2 puts this brighter area at proper black level, but now the rest of the image is not biased high enough to see image detail in the dark parts.


If you're interested in this mod I can write it up and take pictures for you. If you're not handy with a soldering iron (or know someone that is) I'm afraid that I don't have another solution for this. (Maybe someone else does, but I've tried asking before).


Cary
 

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Discussion Starter #3
Cary,


Thanks for your comments.

Yes... I'd be very interested to read about your modification. I'm not sure that I'd trust my soldering capabilities on such a critical bit of the projector but I can get a friend to do it for me.


I'm afraid I was one of the people who was using the "internal pluge" term....I'm not sure who started it but no one ever corrected it until recently. (That was yourself...if I recall correctly)


Hopefully someone else might pick up on this matter this time (Mike, Curt are you watching ??)


Brian.
 

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I really think the easiest way to set G2 on these is to display the internal crosshatch pattern, turn the contrast and brightness all the way down, and turn up each G2 until you just see a raster, then back down until it just disappears. That will get you 95% in the ballpark. Then turn brightness and contrast to 5, display a gray scale test pattern from the Avia or VE test DVD's, and balance the red and blue G2's to get a good gray scale. Ideally, "black" should be obtained with the brightness control at 5.


Chuck
 

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If you carefully read the section in the manual that refers to the 1 volt peak to peak signal -- you'll notice that the G2 adjustment is done without using the signal generator at all.


The next section where you verify the voltages is done using the signal generator.


Chuck's advice is exactly what I did to adjust my G2 levels on my ECP 4101. Worked ok for me.


Roo
 

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Hi Andrew, were you able to get rid of the "bright half" of the screen during dark scenes? If so, is the detail in the dark scenes ok? I have another ECP PJ that I'm setting up and if there's a way that I can get good results without soldering, I'd rather do that of course. I have already verified that it does the same thing as my 3101 though (it's a 4100 and right half of screen is brighter during dark scenes).


Anyway, I'll certainly try calibrating G2 with Avia's gray bars.


Cary
 

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I have a ECP 4500. I also notice that the screen is darker on one side than the other. But I can only see it when I turn off my source. I can never see it when a source is being fed to my projector.


Kevin C. :)
 

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Kevin,

I have noticed that also. I only see the "internal pluge" when there is no signal. As soon as an input is detected the screen goes black.


Chip S.
 

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Quote:
Originally posted by Kevin Coleman
I have a ECP 4500. I also notice that the screen is darker on one side than the other. But I can only see it when I turn off my source. I can never see it when a source is being fed to my projector.


Kevin C. :)
I think what you guys are seeing is Electrohome's attempt at contrast modulation to overcome the effects of the blue and red tubes being on the outside. Do you see this in the green tube? I'm betting no. And I'll bet you see the brighter side on the red is the darker side on the blue, and that the brighter side of the red will be projected on the side of the screen that is the farthest side from the red tube. Similarly, the bright side of the blue tube will be projected to the side of the screen farthest away from the blue tube.


Chuck
 

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Hmmm, I'm curious about the guys that only see this when no source is applied. Does that mean that G2 is turned up high enough that when a source is applied, and the image is black, that the CRT is biased up high enough (either through G2 or brightness) that the background raster is "as bright" or brighter than the "bright half".


Chuck: I can't speak for the other fellow, but I see this on all three tubes, all on the same side of the tube face. This is what made me drag out the scope. If you look closely at the tube face, you can *clearly* see that the bright area is caused by the raster lines hitting the edge of it's field, looping back around to retrace, and not going dark (invisible) until it gets about half-way back to the starting edge. You can clearly see each individual raster line doing this, on all three tubes.


There is no horizontal blanking during retrace, and to make things worse, there's a clamping circuit on the neck board that even lifts the video signal up about 50mv during the clamp time, which starts at the end of the raster and ends about halfway back to the start.


I've tried everything I could to get rid of this. I could raise G2 high enough to swamp out the "bright half" (raise the overall raster bias to overcome it) but then I might as well have a digital projector because black isn't black any more.


If somebody has been able to dial in there PJ controls/pots to get rid of it, I'd love to see it. (Not meant as a challenge, I just want to get to the bottom of this whether I'm wrong or not).


Cary


PS. I wonder if the guys that don't have a problem with this have a source that outputs "blacker than black". Mine does not do "blacker than black" (Skyworth DVD player).


PPS. Brian, kinda off topic, but you said your Skyworth's output (just noticed you had one too) is weak. Mine is ok at 0.7Vpp but if you search in the DVD Hardware section, I posted about a resistor change to it that brings the output voltage up.
 

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I feed my ECP with a FE Quadscan 2.05b at triple (720p). I haven't ever seen the so called 'internal pluge' to my recollection.


My image might be a little on the dark side, but not to the point that people complain.


Roo
 

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I have a 4101 and I also see this on all three tubes. I adjusted the G2 as per Chucks suggestions and it isn't noticable to me during a movie.


Tim
 

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Discussion Starter #13
Hi everyone,


Thanks for your comments


Andrew :


I found the service manual a little confusing with regard to the rgb generator.

Section 4.7 (step 2) isn't too clear on when you should have the signal generator on or off.


Step 1(d) suggests that you connect a generator with a white field to the projector. Now, I'd interpret that step as having the generator on .... is that correct ?


There is no mention of turning the generator off in step 2 .... I'd assume that step 2(b) has the the white field "on" to present a signal to the projector while you adjust R8 with the crosshatch displayed.


What confuses me is the instruction in Step 2(c) to display a crosshatch. Does this imply that you shouldn't be doing step 2(b) with the croshatch displayed


Chuck, Cary, Kevin, Chip :


I can see the "bright half" in all three tubes _ I'm trying to aviod using the "internal pluge" term to avoid confusing anyone else!


I can appreciate the suggestion (Kevin, Chip) that I should ONLY be seeing this when there is NO source connected.......that was my thought..... that the "bright area" is only seen when there is no signal present. Is that my problem ?..... should I be doing this set up without a source (rgb generator) connected. If that's correct, I'm mis-interpreting the instructions in the manual (see comments to Andrew above).


Chuck :


I tried your suggestion last night. Unfortunately, I didn't write down what you said correctly and I was trying to 'see' the crosshatch rather than the raster_ I wasn't having much success although I did "fudge" something that slightly improved my previous situation. When you suggested turning the brightness and contrast right down...... did you mean to zero ? or did you mean to a low level ? On Star Trek :TMP, with the brightness set to 5, I wasn't seeing the "bright half" but I was losing detail in the blacks. Turning the brightness up improves the detail but brings back the "bright half". I'll have another go tonight.


I'm sure I'm close to setting this correctly and it's just a matter of getting the balance right.


WARNING : This next paragraph might be rubbish. Please correct me if I'm wrong, as I wouldn't want to spread any wrong information.


My own thoughts on what's happening here were to do with the "threshold" voltage which turns the tube "on". I wondered if the problem was related to this threshold voltage being set too high so that when a low voltage signal (representing black or darkest grey) was present, the tube would be set "off" and it would display the "bright half". I wondered if this was somehow related to the signal generator output voltage being 0.7v rather than 1.0v and I wondered if the lower voltage from the generator would mean that the "black levels" were below the threshold to fire up the tube.


END OF WARNING


As Cary asks.... Is this something that just needs adjustment or is it something that should be fixed on the video board.


Cary,


I presume that the Skyworth will output "blacker than black" when it's running PAL. Now there aren't really many (any?) PAL test discs that can be trusted (in the same way that we can "trust" V.E. or Avia) but I think that I do have a disc somewhere that has a PAL greyscale on it. I'll see if I can find it and give it a try.


I'm not so sure now if the Skyworth output is on the low side ..... it might just look that way ... because of this problem. I did read your post on the DVD Forum but I thought I'd leave things alone on the player.


Brian.
 

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Discussion Starter #14
Hi,


Chuck :


I had another go at your 'set-up' suggestions last night. I'm still seeing the "bright area", although it's not as noticeable as it was and the blacks have improved a bit.


Many thanks for that.


I'd still like to get rid of this effect .... has anyone got any other suggestions ?


Brian.
 
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