NEC's AKB circut - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 78 Old 01-22-2001, 07:34 AM - Thread Starter
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I have a greenish-grayish line across the top of my scene that I can't get rid of, in an earlier post Bill had told me this is the AKB circut, which controls "auto white balance"...ok good enough.
However I have gone into page 2 of the "source info" menu and turned this thing on, and off...and on and off...and on and off, you get the idea, it just won't shut off.
Do any of you NEC owners have any tricks to shut this annoyance off???
Thanks Kenny
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post #2 of 78 Old 01-22-2001, 08:14 AM
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Kenny,

When you turn the AKB off, do you exit the menu and save the change? I think you have to do that. It should make the reference line disappear. If you exit the menu and save the change and the line is still there, if you go back to page 2, does it still say it's off?

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post #3 of 78 Old 01-22-2001, 08:33 AM
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KennyG,
Chuck brings up a good point, if the menu says off and its still on then the system is working but not seeing the change. If this is the case there is a test-normal switch on the video out board, make sure this is in the normal position, there is a white sticker that shows the position of this above the board on top of the metal cover. Doug
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post #4 of 78 Old 01-22-2001, 12:03 PM
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Good call on the test switch, Doug. Forgot about that one. ;-)
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post #5 of 78 Old 01-24-2001, 11:34 AM
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How much blue defocus was done for the HD source? I'm finding that considerable (more than provided by the blue focus tracking mechanism)blue defocus is needed for the XG's to get good grayscale with 1080i. That would also create the grayscale problem you are seeing.

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post #6 of 78 Old 01-24-2001, 01:58 PM
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This is not a gray scale issue, as much as it is a Hardware level problem. The NECs have a output/bypass switch on the video outboard that Doug described earlier. This is where factory Gray Scale is done with a Scope and Voltage meter. When out of test mode you have full control over the user level gray scale (kelvin) adjustments. All calibration should be done with these, not the reference levels. The reference levels are used in conjunction with the test mode, and measured with a scope and voltage meter. In addition to the reference levels, the most sensitive/important adjustments are the POTS on the Video Out board. That is square one, reference level adjustments is square two, and when you are done with these, you have a proper "factory" calibration, based on wave forms and voltage. From there you can adjust gray scale with Kelvin adjustments.

The six dollar question is - How do you adjust if you are not Scope literate, but you know the factory settings have been changed via the reference menu and POTS?

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post #7 of 78 Old 01-24-2001, 02:39 PM - Thread Starter
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Guys, where is this "video output" card...and do I need to pull the projector down from the ceiling to get to it?
Thanks Kenny
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post #8 of 78 Old 01-24-2001, 03:09 PM
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Kenny, it's in the card cage at the rear of the machine. Once the main cover is off, the card cage cover is the metal with holes in it which covers the rear 1/5 of the projector. The video out card is inside the cage. You'll see white stickers on the card cage cover which identify the boards. The only thing you should do is make sure the AKB SW is in its normal rather than test position. Beyond that, you need a tech. Even I wouldn't do the alignment. I'm in the opposite of Jeff's position. I have scope experience and no service manual. Lack of either leaves you dead in the water.


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post #9 of 78 Old 01-24-2001, 04:45 PM - Thread Starter
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Thanks Guy.
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post #10 of 78 Old 01-24-2001, 09:35 PM
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Hi Doug and Chuck:

I recently worked on an XG, where I could not get the color balance right. I could calibrate a number of different inputs to get a proper gray scale, but when we went to the HDTV source, the upper end of the grayscale is very green/yellowish. When I used the internal test patterns, we would get good top to bottom results, but back out of the pattern, and YUCK! Turning AKB on via the PIC-Function/brightness control would give us an flash of UGLY color, followed by our poor color balance for this input.

I remember that part of the full NEC gray scale calibration from the service manual requires voltage testing when toggling between test and normal on the video out board. I hate like heck to go that deep into this problem, but I am fairly certian that is the fix.

Am I correct that we want to calibrate the Green output to be identical both with the test switch in and out. The change to this is on the video out board - correct. I will REALLY be messing with this projector if I go to this extreme right? I am thinking of marking the POTS with a marker, but even then, I will not have a scope to really look at this, only a voltage meter.

What do you guys think?

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post #11 of 78 Old 01-25-2001, 05:57 AM
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My SVC Manual can travel if you can Guy! I would love to show you the proper calibration of the XGs if you taught me proper use of a scope. I can order one up for a week long rental here in Detroit, and we could master the process! Private email please.

Jeff


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post #12 of 78 Old 01-25-2001, 08:30 AM
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Guy,

Sorry, I didn't realize you just needed service info. I'll be happy to fax you anything you need from my service manual.

Jeff,

I can't imagine that performing any of the scope related adjustments will cure a gray scale problem that only shows up in one source, especially if the internal projector patterns look good. What HD receiver are you using?

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post #13 of 78 Old 01-25-2001, 05:44 PM
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Thanks. Doug Baisey has been trying to get me a manual, but thus far no joy.

Jeff, in lieu of a a hands on lesson, "The Complete Book of Oscilloscopes" by Stan Prentis ISBN 0-8306-3908-X is an easy read and gives you the basics.

Kenny, was the AKB switch in the test mode instead of normal?



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post #14 of 78 Old 01-25-2001, 07:25 PM - Thread Starter
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I just pulled the covers off and checked it, and yes the AKB switch was in the test position...unfortunately it was for a good reason, when I turned it the normal position it turned off my blue and red guns. So until I send this unit in for repairs it looks like I'm stuck with it on. This unit has some other problems too, (brightness controls don't work) and the previous owner has said he'll take care of it, I just hate to be without it for long period of time. I wish I'd been informed of these problems before I bought it...oh well, let the buyer beware.

[This message has been edited by KennyG (edited 01-25-2001).]
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post #15 of 78 Old 01-25-2001, 09:23 PM
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That explains why your brightness control doesn't work. In test mode, the brightness control is not functional. There is some hope provided the previous person didn't tamper with the pot control settings. If only the digital controls are messed up then you can probably get back into business by resetting the reference white controls to proper values. If they are incorrect, then the guns won't be turning on correctly and you'll get the symptoms described when you turned AKB back to normal. As a starting point, try setting them to something which is roughly right. My current ones are....

Drive Control: Red 42, green n/a, blue 34
Brite Bias: Red 59, green 64, blue 58
Brite Gain: Red 50, green 50, blue 50
Black bias: Red 51, green 45, blue 49


If you set your machine's reference white settings to the above, it won't be quite correct, but at least you should see all three guns still functioning with AKB switched to normal.

NOTE: Innocent readers should NOT go into the reference white balance and mess with the settings. Kenny is in a situation in which the settings have already been mucked about per his previous posts about adjusting black bias, etc up and down. Since his machine is already on the ropes with settings which are probably way off, it is reasonable to enter a set of values which work on another machine. These values are by NO means intended to indicate the correct settings for a particular machine other than my own. END NOTE.

Once you have entered the new reference white balance values, let us know if all three tubes now work more correctly with AKB back on normal. If this step helps the situation, then there is hope that the pots have not also been incorrectly adjusted. If those are messed up then, it's definitely technician time. If you report back that indeed things are improved by the above values, then we can have you perform a G2 adjustment to make the values more correct for your machine.



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post #16 of 78 Old 01-25-2001, 10:27 PM - Thread Starter
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Guy, before I go in and change these settings, let me tell you what I have at this time, perhaps I don't need to do that.

Drive control: Red 47 Green N/A Blue 51
Bright Bias: all set to default (50)
Bright gain: all set to default (50)
Black bias: Red 59 Green 59 Blue 60
White balance: Red wht 48 Green wht 50 Blue wht 51
blk 48 blk 50 blk 51

Once I got the kind of picture quality I wanted I made a print out of all my settings.
Another thing, it's all my brightness controls that are not working, brightness, bright bias, and bright gain. I can run them from one end of the adjustment to the other and see no change in picture quality.
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post #17 of 78 Old 01-25-2001, 10:38 PM
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They are different enough that they could be making those tubes go dark when AKB is switched back to normal. Try this.....

1. Set your color balance controls to 50/50 for all three guns. Yes, that will through grayscale out of whack for now. Write down your original settings (you already have I see)

2. Display the Black Bars + Log Steps pattern in AVIA (Title 1, Chapter 3)

3. Set AKB switch to TEST position.

4. Peer directly into your tubes and adjust reference black bias (G2) for each tube and make the raster just light up and then go back down one click. Don't do this by looking at the projection screen. You must look into the CRT directly to see the very dim details which are vital to this maneuver.

5. Set AKB switch to NORMAL position. The picture will most likely get very dark again.

6. Again, peer directly into each tube and for each tube adjust reference bright bias (not gain, leave gain at 50) to make the black background of the pattern just barely light up in the tubes.

Does that make things better and allow proper control with AKB switch in normal position? If not, then I'll bet the pots are maladjusted.

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[This message has been edited by Guy Kuo (edited 01-26-2001).]

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post #18 of 78 Old 01-26-2001, 06:50 PM - Thread Starter
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Sorry I haven't gotten back to you, but it's been a nasty day at the office, one thing after another, I've been fighting with generators all day and I'm dead tired, so I will battle projector tomorrow.
Tonight all I want to do is sit down and watch a movie.
Good night and happy viewing, Kenny
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post #19 of 78 Old 01-26-2001, 07:49 PM
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Good. Go relax and enjoy. After all.....

Projector battle + tired = dead projector +/- owner

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post #20 of 78 Old 01-27-2001, 06:57 PM - Thread Starter
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WOW what a difference!!! It worked, Guy I did as you instructed in all I can say is thanks a million!!! The picture is so much better, I can't believe this.
Before the flesh tones never were right, in dark scenes they washed out, and in bright scenes there was to much red.
After I put the test switch in normal the whole thing has just fallin' into place, the fleshtones look great in bright or dark scenes.
I've been tweeking every movie I have watched to try and get these tones correct, and never did. I think all the tweeking is about over.
It just amazes me as to how easy it is to adjust the color balance once the "switchology" is correct!!!
Once again thanks alot, and especially Guy...now I'm truely blown away by this picture.
However, I now have a new problem, my screen is larger than my actual picture size, and during dark scenes the area around the picture is lighter than the picture. What is that? When the test/normal switch was in test this didn't happen, the area around the picture was always as dark or darker than the picture, I'm sure this is how it should be, because the picture is awesome.
I suppose now it's time to make a frame that I can mount to the screen...or sell this screen and get the correct size...after the last month of frustraton this is nothing.

Kenny
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post #21 of 78 Old 01-27-2001, 08:02 PM
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You are welcome, Kenny. Now which calibration disc are you recommending to friends? http://www.avsforum.com/ubb/smile.gif

If the raster is lighting up around the picture but blacks in the picture are black, then the G2's are probably still set one or two clicks too bright.

Since you've had success with the above and your pots seem to match the photo from my machine, let's have you redo a baseline calibration.

----- Note ----
The quick and dirty procedure which was in this posting has been deleted. A more complete procedure which correctly sets G2 voltages appears later in this thread.

GK

[This message has been edited by Guy Kuo (edited 02-11-2001).]

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post #22 of 78 Old 01-27-2001, 08:06 PM
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Oh. I almost forgot. Once G2 (black bias) is corrected, you can go ahead and close down screen blanking on all sides.

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post #23 of 78 Old 01-27-2001, 10:53 PM
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Hi Guy,

When you are saying "G2", you are referring to the reference black bias adjustments and the pots on the video board, right?

Thanks,

Vance


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post #24 of 78 Old 01-27-2001, 11:19 PM
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Guy,
These are great posts, informative and well written. The reference white balance menu has four submenus. You've mentioned setting the black bias with the AKB switch set to test, and then the bright bias with the switch set to normal. You then suggested setting gray scale using the drive and bright bias controls. What you haven't mentioned is the bright gain control. When and how might that control come into play? How would you describe the role of each of these controls (drive, bright bias, bright gain, and black bias)?

Vance,
Guy was referring to black bias on the NEC XG series, which is controlled by the remote while in service mode, accessed by using the service passcode. Its in the reference white balance submenu of the reference adjustment menu. You hit the ADJUST button, put in the service passcode (315151) and then ENTER, hit the 9 button (for REF. ADJUST), hit the 6 button (for REF. WHITE BAL.), and this will produce a menu with submenus for DRIVE CONTROL, BRIGHT BIAS, BRIGHT GAIN, and BLACK BIAS.

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[This message has been edited by Steve Goff (edited 01-28-2001).]

[This message has been edited by Steve Goff (edited 01-28-2001).]

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post #25 of 78 Old 01-28-2001, 10:31 AM - Thread Starter
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Guy, I want to thank you for the considerable amount of time you have spent helping me through all of this calibration.
I have copied all your baseline cal instructions and will complete them in the next day or two...one question, item 12 under "Calibrating baseline grayscale" you say "use referance drive (red & blue)"...is this the "drive control" adjustment?
YES I only recommend AVIA http://www.avsforum.com/ubb/smile.gif Kenny
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post #26 of 78 Old 01-28-2001, 12:02 PM
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Kenny, yes, I'm refering to the reference white balance drive controls for red and blue.

Vance, the controls are not the pots, but digital controls accessessed as mentioned by Steve.

Please ALL, these adjustments normally never need to be done except by a technician and one must not lightly undertake them. Kenny's machine was definitely off kilter and under that particular circumstance it was appropriate to straighten out the controls to something more normal. This is not the full factory procedure which adjusts the pots to presumably attain predetermined signals levels prior to the fine calibration done with digital controls. Caution is warranted.

Kort, if you are using a Toshiba based DVD player, be sure to turn subtitles on and back off once you are in the menu system. Some of the Toshibas won't show the button hilighting in AVIA unless you do that. Makes for a frustrating time navigating the disc.
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post #27 of 78 Old 01-29-2001, 02:15 AM
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Doug was kind enough to inform me about the proper setup procedure for reference white balance. Based on that information, I recalibrated my XG135LC. Black level retention and cutoff point is better behaved. "Legends of the Fall" showed more consistent shadow detail after this process. Surprisingly, the marked blue hump in my 1080I grayscale for which I had to do massive blue defocusing to tame is also smaller. This may help with Jeff’s problem which sounds quite similar.

The steps described here are only a subset of the service manual procedure along with some modifications I added to get the red and blue guns into better grayscale tracking. This process can be done with just AVIA, a digital mulitmeter, and colorimeter, but should only be attempted by a technician level user.

THIS IS STRICTLY AT YOUR OWN RISK. THE PROCEDURE WORKED ON MY MACHINE, BUT I CAN’T GUARANTEE AGAINST DEVASTATING RESULTS.

Be aware that this method assumes that the signal level pots in the machine have not been disturbed from properly calibrated state. This means the signal levels reaching the white balance circuit must already be correct. Recalibrating the pots properly requires a oscilloscope and we’re NOT going to cover that here. If that is needed, then a service tech should be contacted.

Allow the projector to warm up for at least 20 minutes prior to making any adjustments.

You’ll need the AVIA disc in the DVD player and color saturation in your video processor turned all the way off or the Pr & Pb lines of the player disconnected. This ensures that no color contaminant from the AVIA disc confuses matters. Otherwise, the low end of the grayscale may be thrown off by about 300 Kelvin. Granted, that’s not much, but if you’re going to do this, it may as well be as accurate as possible.

Set your processor to output a line doubled signal. A higher scan rate signal could be used but a 480P signal more closely mimics the needs of a 1080I signal. This seems to be important for tuning out the HDTV blue hump which was horrible on my machine. The service manual uses a NTSC or PAL test signal. I used an RGBHV signal and assumed that signal levels were already correct since my machine was already working well.

If your processor or HTPC has a brightness control, set it to midpoint or a setting which is known not to clip the black bars in the test pattern. You can verify the black bars are being output from a HTPC by hooking up to a CRT computer monitor.

Temporarily turn blue focus tracking OFF in the settings menu.
Display a focus pattern in blue and adjust center blue em focus for sharpest image.

Turn blue focus tracking back ON. This sets the amount of blue defocus to be just that created by the projector rather than some amount you have manually dialed in.

Set Kelvin color temp to center and wht & blk to 50 for all three guns

Open blanking maximally for all directions

Set Brightness to 60

Set Contrast to show a 100 IRE window at the normal white level for the system. The service manual procedure sets contrast to 100 but that works only if you have totally verified signal levels with a scope. Since we’re assuming already correct signal levels, I simply left my contrast at 43 – the setting that generates a normal white level 10.5 FL at my screen.

Set AKB switch to TEST position!!!!!!!!!

Set your DMM to DC volts and measure TP 7404 (red G2), TP 7504 (green G2), & TP 7604 (blue G2) and verify that the voltage is 2.5 +/- 0.1 at each point. If it is off that target, call a service tech. More needs calibrating than can be described here.

Your DMM should have an insulated clip to connect to the test points. Never try to hold a plain test probe in position or you risk shorting the projector. You can use the metal shield as ground.

Display AVIA Black Bars + Log Steps pattern (title 1, chap 3)

Note: controls in all caps are those in the reference white balance menu.

Adjust BLACK BIAS for each gun to make the raster beyond the edge of the pattern just barely light up. Do this by looking directly in the tubes. Looking at the projection screen isn't senstive enough. Indeed, most of this procedure is done by looking in the tubes rather than the screen.

Remember, the "raster" is the portion of phosphor which is painted by the electron beam. It extends beyond the image area and should not be confused with the image area. Under every day operating conditions the raster is not lit up and one only sees the image area illuminated.

Now you have set the black bias (G2) to roughly their correct position. Later you'll readjust them to hit 2.5 volts at the test points.

-----------------
Set AKB switch to Normal position!!!!!!!!

Display AVIA Vertical Crossed Gray Ramp Pattern (title 1, chap 105)

-----------------------
Look directly into the green tube and you’ll see brightness ramps going vertically in opposite directions. Pay close attention to the dark edge of either ramp. Set green BRIGHT BIAS to the point that just barely makes the dark edge go black instead of lighting up. The idea is to make the barest amount of the ramp to go black, but some must go completely black.

Set green BLACK BIAS to make the test point TP 7504 (green) read 2.5 volts +/- 0.1 volts. Don’t get the controls mixed up!

Now begins an adjustment loop which you will repeat until the measured G2 voltage no longer deviates from 2.5 volts when you readjust and then remeasure at brightness set to 60

Begin Green Loop -----

Set Brightness to 0

Look in the green tube. You will see the ramps are now much darker. Find the edge for each ramp at which it goes black. Adjust green BRIGHT GAIN to make the black edges just meet in the center of the screen. Basically you’re setting BRIGHT GAIN to make 50 IRE, the middle of the ramps, be the point at which things go black.

Set Brightness back up to 60

Remeasure green G2 at TP 7504.

If green G2 still reads 2.5 volts +/- 0.1 then exit Green Loop

Otherwise, readjust green BRIGHT BIAS (not black bias!!!!) to once more achieve 2.5 volts.

Repeat this loop starting at "Set Brightness to 0"

End Green Loop ------
-------------------------------------------

Now redo the same for the red gun…..

Look directly into the red tube and you’ll see brightness ramps going vertically in opposite directions. Pay close attention to the dark edge of either ramp. Set red BRIGHT BIAS to the point that just barely makes the dark edge go black instead of lighting up. The idea is to make the barest amount of the ramp to go black, but some must go completely black.

Set red BLACK BIAS to make the test point TP 7404 (red) read 2.5 volts +/- 0.1 volts. Don’t get the controls mixed up!

Now begins an adjustment loop which you will repeat until the measured G2 voltage no longer deviates from 2.5 volts when you readjust and then remeasure at brightness set to 60

Begin Red Loop -----

Set Brightness to 0

Look in the red tube. You will see the ramps are now much darker. Find the edge for each ramp at which it goes black. Adjust red BRIGHT GAIN to make the black edges just meet in the center of the screen. Basically you’re setting BRIGHT GAIN to make 50 IRE, the middle of the ramps, be the point at which things go black.

Set Brightness back up to 60

Remeasure red G2 at TP 7404.

If red G2 still reads 2.5 volts +/- 0.1 then exit Red Loop

Otherwise, readjust red BRIGHT BIAS (not black bias!!!!) to once more achieve 2.5 volts.

Repeat this loop starting at "Set Brightness to 0"

End Red Loop ------
-------------------------------------------

Same for the blue gun…..

Look directly into the blue tube and you’ll see brightness ramps going vertically in opposite directions. Pay close attention to the dark edge of either ramp. Set blue BRIGHT BIAS to the point that just barely makes the dark edge go black instead of lighting up. The idea is to make the barest amount of the ramp to go black, but some must go completely black.

Set blue BLACK BIAS to make the test point TP 7604 (blue) read 2.5 volts +/- 0.1 volts. Don’t get the controls mixed up!

Now begins an adjustment loop which you will repeat until the measured G2 voltage no longer deviates from 2.5 volts when you readjust and then remeasure at brightness set to 60

Begin Blue Loop -----

Set Brightness to 0

Look in the blue tube. You will see the ramps are now much darker. Find the edge for each ramp at which it goes black. Adjust blue BRIGHT GAIN to make the black edges just meet in the center of the screen. Basically you’re setting BRIGHT GAIN to make 50 IRE, the middle of the ramps, be the point at which things go black.

Set Brightness back up to 60

Remeasure blue G2 at TP 7604.

If blue G2 still reads 2.5 volts +/- 0.1 then exit Blue Loop

Otherwise, readjust blue BRIGHT BIAS (not black bias!!!!) to once more achieve 2.5 volts.

Repeat this loop starting at "Set Brightness to 0"

End Blue Loop ------


From now one do NOT readjust any of the green gun controls in the reference white balance. It will serve as the axis around which the other two guns are fine tuned for grayscale.

Set D65 grayscale using a colorimeter. Use the red and blue DRIVE CONTROLs while displaying an AVIA 100 IRE white window (title 1, chap 22) to set the bright end of the grayscale. Set the low end of grayscale using red and blue BRIGHT BIAS controls and an AVIA 30 IRE white window (title 1, chap 15). Again, do not adjust the green gun controls.
It will take several iterations to get both ends of the graycale to measure D65.

The service manual includes checks for overvoltage at this point, but I do not include that check since we assume that signal levels are already okay and we are already at or near final contrast setting.

Since you have probably slightly altered red and blue BRIGHT BIAS in getting the red and blue guns to track with the green, G2 voltage may have changed for red and blue. Recheck at the G2 test points for red and blue for 2.5 volts. If either or both have changed, readjust using BLACK BIAS for the appropriate gun(s) to once more hit 2.5 volts. That is BLACK BIAS not BRIGHT BIAS!

Verify that all three G2 test points are at 2.5 volts +/- 0.1.

Verify that setting AKB switch to test position only makes a minor change in screen appearance. A little change is okay. If there is big difference between the positions, something is amiss. Leave the AKB switch in normal position

Redo brightness, contrast, and Kelvin fine calibration for each of your video memories. You should find that the Kelvin controls won’t need much more than minor changes and brightness will end up about 60.

------------------
Guy Kuo
www.ovationsw.com
Ovation Software, the Home of AVIA DVD




[This message has been edited by Guy Kuo (edited 02-01-2001).]

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post #28 of 78 Old 01-29-2001, 08:44 AM
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Guy:

I am speachless. You have done an excellent job converting the Service Manual documentation, and making it usable. Great Job. I will use this as a reference document for future installations.

Jeff


------------------
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-the audience is watching, just not enough HiDef CONTENT!-
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post #29 of 78 Old 01-29-2001, 03:30 PM - Thread Starter
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Alright, I'll get on these corrected baseline cal's within the next week or so, I'm just going to enjoy a few days of "tweek-less" bliss!
I can definitely live with this picture for a few days...come to think of it I've gotta fight with the htpc and get winDVD and powerDVD to co-exist, winDVD just doesn't work as well as powerDVD...the picture is better (by a very small margin) but I get more glitches in a single movie with winDVD than I get in two weeks of using powerDVD. I average about 3 glitches per movie with winDVD, and had not one glitch in 7 movies (two weeks) with powerDVD....the fun just never stops!
Thanks to all of you, especially Guy, and Doug for the updated info. Kenny
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post #30 of 78 Old 01-29-2001, 03:36 PM - Thread Starter
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I don't know where my post went, but I'll try this again.
Basically I was just thanking all you guys for the help...Guy for your steadfastness, and Doug for the cal update.
I will get on this updated recal in a few days, at this point the picture is very good, and I just want a few days of "tweek-less" bliss.

I don't have access to a colorimeter rental, so Guy I'm going to build your "solar cell" unit.

P.S. Well I now see both of the post have shown up...I suppose two are better than one. Anyway, Guy, last night I did your "quick-n-dirty" baseline cal, and now the raster around the image area is unlit.

Thanks again!!! Kenny

[This message has been edited by KennyG (edited 01-29-2001).]
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