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Trimpot Adjustment/Surgery

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Someone asked how the blue trimpot can be adjusted without a color analyzer.  Video calibrator Michael TLV responds below:

"Trimpot Surgery ...

I've actually been where you are, but I messed with all three on purpose ... which I bet is the case with you and your blue POT.

Don't turn off the other two guns when you are adjusting the trimpots to correct for only one colour. Don't even cover them up. You need to see the interaction between the three crt's. The way to do an eyeball correction of the trimpots is:

  1. Bring up a black background.
  2. Turn the trimpot (blue is this case) through its entire range and observe what happens to the black. You see it go from the point of being  black to blue black. At the extreme end of the blue knob, numerous arching blue lines appear. This is too far.
  3. You want to keep backing off the blue in the picture until the image becomes black to your eyes. Not black with the blue tint. Stop when you reach this point.
  4. Now bring up a test image of a person ... for flesh tone adjustments.  I often use the lady in the A Video Standard disc ... chapter two Frame 4300 from Laserdisc. But there are good frames also in VE and other  sources ... like Pleasantville.
  5. Adjust the R/G/B Cut and Driver controls to smooth out the flesh  tones.

That's the way to eyeball it should you mess it up. Professionally speaking, only a colour analyzer will truly get you back to normal.

Now here is another approach for those that are bold and want to mess with the three trimpots ... not by accident. You notice that when you turn the blue trimpot, it affects the thickness of the blue gridlines on the  convergence pattern. For those who think that the blue line just seems too fat and out of focus ... adjusting the trimpot can actually reduce the thickness of the blue line to get it more in line with the red and green.  This is something that I have done on occasion to all three crt's to tighten the thickness of the bars. You have to still create that black background when you are done. Final colour adjustments are made with the colour analyzer to make things completely right.

** Note: If you try  this, you will decrease the light output from the RPTV somewhat.