How to remove a blue cast from near blacks on a Hitachi RP-CRT? - AVS Forum
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post #1 of 21 Old 06-03-2014, 08:22 PM - Thread Starter
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I have a Hitachi 57S715. I've calibrated it with my X-rite Display Pro 3 using HCFR. HCFR says the Delta E is under 3 for all greyscale points. Most of the values are around 1. However, I'm struggling some with the grayscale. I think I've dialed it in as best as the 2 pt white balance controls allow. The RGB grayscale component mix is quite flat from 30 to 100%. However, there is excessive blue at 20% and even more 10%. This causes near blacks to have a visible blue cast. I'm at a loss how to fix this.

I used the Standard color temperature as my starting point. There are only 5 possible adjustments for each color temperature that I know of in the service menu.

R cut
G cut
B cut
R drive
G drive
(There is no B drive)

If I pull down the B cut to try to reduce the amount of blue at 10% and 20% the delta E gets larger at 30 & 40%. Is there some other control/setting I'm missing that I can use to reduce the amount of blue below 30% specifically in the very near blacks?
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post #2 of 21 Old 06-03-2014, 08:34 PM
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If one of the other color temperatures have a more neutral 10 and 20%, then you might want to give it a try.

Another option is to use a LUTs box and perform a 3D cube calibration.

Given the age of your TV, it'd make more sense to update the TV rather than to buy a LUTs box that cost most of what a new TV would cost.

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post #3 of 21 Old 06-03-2014, 08:50 PM - Thread Starter
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I guess I need to measurement the other color temperatures. Standard was the recommended color temp for calibrating from though. I quasi-calibrated the grayscale on it using a DSLR forced to 6500k color balance shortly after getting it almost 10 years ago. The TV didn't have a blue cast at very low IRE with those settings. I reverted to the factory settings prior to calibrating it with the ID3. Maybe I should go back to those settings and try calibrating it from there though I'm not sure why the end result would be different.
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post #4 of 21 Old 06-03-2014, 08:54 PM
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Reverting back to factory settings is never a good idea. Hopefully, you recorded your settings before that.

If you can't decrease blue, try increasing green and red cuts. You will then need to adjust brightness.

You may also want to stop by the Hitachi threads if you continue to have a problem.


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post #5 of 21 Old 06-03-2014, 09:03 PM - Thread Starter
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Originally Posted by LastButNotLeast View Post

Reverting back to factory settings is never a good idea. Hopefully, you recorded your settings before that.
If you can't decrease blue, try increasing green and red cuts. You will then need to adjust brightness.
Increasing the green and red cuts also increases the red and green at the high end which then requires a reduction green and red drives. This opens up the blue deficit at 40% though. The gamma is pretty high at the low end though like 2.6 -2.7, so I probably should try to add green and red at the bottom as you suggest to increase the low end luminance. I guess I just need to give it another shot and see what happens.
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You may also want to stop by the Hitachi threads if you continue to have a problem.
I've looked through the some of the Hitachi threads. Heck I started one of them. There are lots of posts, virtually none from anyone with a meter. Getting the colors dialed in on this thing was quite challenging to say the least. The colors were very oversaturated at 25/50/75%.
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post #6 of 21 Old 06-03-2014, 10:17 PM
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Lots of us have meters. We were here:

http://www.avsforum.com/t/790702/hitachi-51-57-65f59a-crt-rptv-tweaks-thread

You may also want to get in touch with Bob:

http://www.avsforum.com/t/695922/dont-dump-your-crt-rptv


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post #7 of 21 Old 06-03-2014, 10:21 PM
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This is actually a pretty common issue with CRTs: The measured blue and gamma going "high" at the dark end. In the old days, most folks stopped measuring at ~30% or 25IRE.

One thing that sometimes helps is reducing the contrast/white-level so that the blue gun doesn't have to work as hard at the bright end. This in turn might give you a little more "wiggle" room at the dark end ... or not.

We are sometimes "shocked" when we go back with modern tools and find that our "beloved" displays weren't quite as good as we thought they were ... back in the day.

This is one of those situations where you might have to make a compromise. Your best bet at this point is to seek MrBob's advice.
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post #8 of 21 Old 06-04-2014, 04:53 AM - Thread Starter
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Originally Posted by HDTVChallenged View Post

This is actually a pretty common issue with CRTs: The measured blue and gamma going "high" at the dark end. In the old days, most folks stopped measuring at ~30% or 25IRE.

One thing that sometimes helps is reducing the contrast/white-level so that the blue gun doesn't have to work as hard at the bright end. This in turn might give you a little more "wiggle" room at the dark end ... or not.
Oddly, I reduced the white level quite a bit from where it was previously. There was no visible cast to to the blacks before. If there had been a cast I couldn't get rid of I would have replaced the TV a long time ago with something else.
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This is one of those situations where you might have to make a compromise.
I guess so. The blue blacks are a non starter for me. I was perceptually much happier with my prior grayscale settings even if the measurements say they're wrong. I will try rolling back & maybe tweaking them some until I get something that looks better visually to me in the very low IRE's while measuring as good as possible and then see about making a 3D LUT for madVR. I watch movies and OTA HDTV mostly from my HTPC, but I do watch some cable and I don't want the blue cast on the cable.


By the way, thanks for the replied guys.
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post #9 of 21 Old 06-04-2014, 06:02 AM
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Just because the measurements say that its wrong doesn't always mean that they are.

Everything from faulty software, to drifted meters, to usb ports not suppying enough power, to using a meter profile that doesn't register until you click on it a few times.

Don't overlook you computer either. I recently loaded Calman onto my desktop to see if there were any differences and there were. Better calibration results with the desktop. I don't particularly want to spend the time to track down what caused the difference only that there is one. If I had to speculate, I'd say that the desktop's power supply is more stable. Only speculating here.

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post #10 of 21 Old 06-04-2014, 07:37 AM - Thread Starter
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Quote:
Originally Posted by JimP View Post

Just because the measurements say that its wrong doesn't always mean that they are.

Everything from faulty software, to drifted meters, to usb ports not suppying enough power, to using a meter profile that doesn't register until you click on it a few times.

Don't overlook you computer either. I recently loaded Calman onto my desktop to see if there were any differences and there were. Better calibration results with the desktop. I don't particularly want to spend the time to track down what caused the difference only that there is one. If I had to speculate, I'd say that the desktop's power supply is more stable. Only speculating here.
I was using a desktop PC, not a laptop. I've calibrated several other displays in my house with my ID3 so I don't have any reason to believe it is faulty. I've been happy with the results on the other displays. On the S715 it shows excess blue at 10% and 20%, but the Delta E is just under 2. Visually those seem okay. It's the levels much closer to 0 that are objectionably blue to my eyes. I should probably do a 21 point grayscale measurement for a little better idea what's going on.

As an aside working the white balance on the Hitachi is a huge pain in the butt because the visible service menu overlay affects the measurements due to internal reflections / ANSI contamination so you have to keep going in and out of the service menu to measure, adjust, measure, etc... mad.gif
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post #11 of 21 Old 06-04-2014, 10:41 AM
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Just a thought: have you ever checked/set your G2 voltages? These set the point at which the CRTs begin to illuminate. Different sets have different procedures (our first CRT RPTV, a Hitachi 40-in. 4:3 display, had G2s set by putting the set on an input with no signal and tweaking the knobs while looking into each CRT to note when it began to light up, while our current Mitsubishi requires additional setup plus a 'scope or digital voltmeter), so you may want to get a service manual if you don't already have one. A drifted G2 can cause the tube to light early, messing up gamma and introducing a tint into the lower end of the grayscale.

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post #12 of 21 Old 06-04-2014, 10:52 AM - Thread Starter
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Originally Posted by Rolls-Royce View Post

Just a thought: have you ever checked/set your G2 voltages? These set the point at which the CRTs begin to illuminate. Different sets have different procedures (our first CRT RPTV, a Hitachi 40-in. 4:3 display, had G2s set by putting the set on an input with no signal and tweaking the knobs while looking into each CRT to note when it began to light up, while our current Mitsubishi requires additional setup plus a 'scope or digital voltmeter), so you may want to get a service manual if you don't already have one. A drifted G2 can cause the tube to light early, messing up gamma and introducing a tint into the lower end of the grayscale.
I have not done that. I would certainly not be opposed to trying something like that, but I'm not sure it's necessary. Prior to my messing with the 2 point white balance 2 nights ago there was no blue cast to near black.

Where would I go about getting a service manual?
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post #13 of 21 Old 06-04-2014, 11:42 AM
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G2s do drift, so it's a good idea to check them every so often. Service manuals for older electronics are available from a number of sources. I've purchased from servicemanuals.net. Depending on the item and its manufacturer, they are available as paper copies, discs, downloads, or as all of the above.

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post #14 of 21 Old 06-04-2014, 01:51 PM - Thread Starter
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Okay, well I bought the service manual as a PDF. I only little blurb about a single High Voltage Adjustment, and a warning not to change it in the field. I don't see anything about G2 or voltage adjustments per color / gun.

There are references the screen VR’s and Focus VR’s on the Focus Pack though. My understanding is that the screen VR basically adjusts the same thing as the CUT OFFs in the menus.
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post #15 of 21 Old 06-04-2014, 02:18 PM
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The screen VR is the G2. It adjusts the voltage floor at which the CRT will begin to produce light. Not quite the same thing as the cuts.

If you do try to adjust them, note that they usually have slots for a Phillips screwdriver in the end of the pot. Using a small screwdriver for the adjustment gives you much finer control, I've found. Without a screwdriver, it's much easier to overshoot/undershoot your target since the pots are very small in both length and diameter.

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post #16 of 21 Old 06-04-2014, 02:30 PM - Thread Starter
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Originally Posted by Rolls-Royce View Post

The screen VR is the G2. It adjusts the voltage floor at which the CRT will begin to produce light. Not quite the same thing as the cuts.
Thanks for clarifying that. Unfortunately, the SM isn't exactly helpful with setting them.

Adjustment procedure
...
(2) Choose “SERVICE” item from I2C adjustment menu by pressing THUMB STICK E.
(3) Screen VR should be turned clockwise gradually and set so that retrace line begins to appear.
(4) Return to “NORMAL” mode by THUMB STICK F again.
...

However, if I turn it counter clockwise very slightly I should be able to reduce the blue component in low IRE values at the cost of overall blue output, correct?
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post #17 of 21 Old 06-04-2014, 02:48 PM
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Honestly, you'll want to set it the way they say. Trying to set it any other way might cause unforeseen issues as it's one of the key baseline settings.
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post #18 of 21 Old 06-04-2014, 04:01 PM - Thread Starter
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Originally Posted by Rolls-Royce View Post

Honestly, you'll want to set it the way they say. Trying to set it any other way might cause unforeseen issues as it's one of the key baseline settings.
Do their instructions make sense to you? It seems to say that you want the retrace line to be faint, but that seems a little nebulous.
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post #19 of 21 Old 06-04-2014, 06:10 PM
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However, if I turn it counter clockwise very slightly I should be able to reduce the blue component in low IRE values at the cost of overall blue output, correct?

Those pots are VERY VERY VERY sensitive. Trust me on that. If you are going to do anything, mark the current position very carefully and make very small adjustments.

You should be able to see the trace lines for each color individually, so, if you're lucky, the blue may actually look too bright/long relative to R and G.

Good luck.

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post #20 of 21 Old 06-04-2014, 09:04 PM
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Do their instructions make sense to you? It seems to say that you want the retrace line to be faint, but that seems a little nebulous.

IIRC, my Hitachi's manual said the same thing. When I tried it, I couldn't see the retrace unless the pot was cranked way up. Eventually, one of the old-timers on a forum I belonged to at the time cleared it up for me.

Essentially, you have to put the CRT in "Service" mode with the joystick (on my old Hitachi there was a sliding switch that did the same thing), then run the pot down until all light disappears from that tube, then slowly bring it back up until you just see the tube begin to glow. That's it. Best to do this in reduced lighting so you can see the brightness change in the tube.
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post #21 of 21 Old 06-05-2014, 05:07 AM - Thread Starter
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Quote:
Originally Posted by LastButNotLeast View Post

Those pots are VERY VERY VERY sensitive. Trust me on that. If you are going to do anything, mark the current position very carefully and make very small adjustments.
You should be able to see the trace lines for each color individually, so, if you're lucky, the blue may actually look too bright/long relative to R and G.
Good luck.
The blue was brighter than the red and green, but adjusting it very carefully didn't end up making any difference. I can put up a 5% gray pattern and get it perfectly gray with no cast according to the meter (and it appears to have no tint to my eye either), but I end up with a huge blue deficit in the mid gray values. When I increased the blue cut to add the missing blue in the mid values the blue ends up dominating at the 5% and darker values again and I'm basically right back where I started.

Ultimately, I backed off the blue cut until the blacks didn't seem visually dominated by blue. The 5% and 10% gray values had a delta E of right around 1 and still had a measurable blue tint, but seemed acceptable visually. This caused some of the mid gray values to end up short on blue with a Delta E of around 5, but they don't seem tinted visually. I will create a 3D LUT for madVR that should clean up the measurements in the middle nicely.

I guess this wasn't a whole process wasn't a total waste of my time since I found the settings to adjust the gamma. Adjusting STATG10 from 0 to 5 lowered my gamma from 2.4 average (rising a bit to about 2.6 at 5% gray) down to 2.2 average (rising to about 2.35 at 5% gray). FWIW, STAGT10 of 0 (which is turning off the Static Y Gamma Black Gain) was basically the same as a setting of 4. I left STATG20 alone at 3 since any changes to it completely messed up the shape of the gamma curve.
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