21CT55 Screen-Shot Test

[old_tv_nut]

Originally Posted by Tomcomm

Wayne...........Screen-shot # 5 displays only one field not a full frame time. In checking the parameters of that jpg shot I noted it's shutter opening time was 1/13 second or quite sufficient for a complete 1/30 second interlaced frame. It is apparent that line-pairing occurred during screen-shot #5 as you observed. Since all the other shots taken within a few minutes had good interlacing, an anomaly had occurred. Early-on I observed that vertical interlace quality is greatly influenced by the front panel vertical hold manual setting, even when the hold is well removed from causing vertical roll. I considered this imperfection to be of secondary importance and accommodated it by manually tweaking the vertical hold to achieve interlace immediately before any quality screen shot. Apparently, I neglected to tweak the vertical hold before shooting #5. I intend to get into the vertical deinterleaver some day to find out why the waveform differential circuitry is not operating correctly…..Tom

Line pairing generally comes from horizontal energy getting into the vertical sync - but it doesn't have to be a sync signal separation circuit problem necessarily. It can also occur due to ground currents from the H sweep getting into the vertical, and this can be very difficult to find and fix, as it depends on the physical arrangement of ground points of the various circuits of the chassis. If the sync circuit itself is clean, then experimenting with extra ground leads and lead dress, or actually moving existing ground points may show some effect.