Monday, August 09, 2010
SuperSprint Repair - Pt 8 - Drawing a blank, or not!
By playing with the drive pots and the screen control, I manage to get a proper picture (pic 4), but the blue pot is all the way down and the other pots are all the way up. Also, the screen seems set a little high at about 11o'clock. At 9 o'clock there is practically no image at all. It's usable, but I wonder about running these pots hard at one end or the other.
Conclusion: It's playable but I'm still not certain where the blue problem lies. I had speculated that the problem was a "hot" blue gun and a weak red and green because of how I set the pots. However, with a good picture on screen, final K voltages are R-87.2, G-88.7, B-101.0 vs 88.3VDC spec for all. What confuses me is that *dropping* the blue gun to 88.3 dramatically increases blue bias and creates raster lines on screen. Perhaps's an inverse coupling of K voltage and screen brightness is normal and I just don't understanding completely how the CRT works.