Quote:
Originally Posted by yagosaga
Why is the yellow of the color bars dim in comparison to cyan and magenta?- Eckhard
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Good question Eckhard. Besides the usual distortions introduced between the CT-100 screen and yours, mine, and everyone else's, the green is weak. By way of explanation, let me share with you this recent email I wrote:
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Those of us directly involved with the 15GP22 project last May at ETF 2007 were relatively pleased with the results, as has been stated before. Not all was perfect of course and so I have attempted to address the most serious anomaly, the poor color bars green-to-magenta transition.
To that end, I acquired a B&K-415 generator with the specific purpose of sweeping the chroma circuitry. Before the first attempt however I used a Fluke 77 to troubleshoot a pesky rare intermittent that has been plaguing me on and off for over a year — bright flashes of green in the picture.
Turns out the Q demodulator plate load resistor was running 50 to 100 percent high depending on how it was bumped. But unexpectedly there were a number of off-value resistors in the R, and G, amps.
As you can see in the accompanying photos, there was distortion in about the first 25-percent of the magenta bar (overexposed screen image shows it off well) before the fix, but a close up now shows much improvement afterword.
With three replacement resistors in the amps and the new 18K plate load the set was stable although no longer calibrated. The picture looked ‘orangey’ with brownish greens.
Last night I ran a complete new calibration beginning with red purity. The results were quite nice. I suspect better than ever.
A word about calibration: before the fix, both the B and G Drive controls needed to be fully CCW; now the picture calibrates with them cranked up somewhere in mid range.
The full range of color on the Robin Hood DVD is back, having been lost after the fix. Purple is royal again; trees are green again; Maid M. has stage-makeup red lips again.
I also touched up the convergence and lucked out as I managed to avoid a slippery slope and the need to start from scratch; photo attached.
The color bar screen photo was taken to illustrate the much improved G-to-M transition, the most technically challenging in NTSC bars, and it was taken before the set was recalibrated.
Henceforth Eckhard, you shall be known as eagle eye.
Pete