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Re: Positional Hum/Color Drift



>The following is forwarded from Alan D. Burnham, Senior Engineer,
>Wickerworks Video, Denver Colorado:
>
>--- Forwarded mail from a.burnham at genie.com
>
>At the same time I have been looking for the cause of color drift.
>(Rank MKIIIC enhanced/Renasance 888/DUI/DigitalVision system.)  Seems the LP X
>FP and LP2 X FP2 waveforms from the shading waveform generator board are AC
>coupled and the DC change during a pan and/or zoom cause a color drift via the
>Festival board.  Also a slow color drift is seemingly caused by the burn cell
>output not being perfectly constant.  The waveform generator problem I have
>resolved by DC coupling the two waveforms butI do not know what to do about the
>burn cell problem. (Seems that the original equipment burn cell power supply is
>at fault but a couple hours looking at it makes me think it is working as well
>as it can.)
>
>Any help on this would be appreciated !  Thanks !
>
>--- End of forwarded message from a.burnham at genie.com
>
The Accuglow burn correction system from DAV is totally DC coupled, and also
helps stabilize the 
burn cell as well. The improvement over the typical Festival/ 807D board set
is dramatic. "Ringing on edges" is
greatly reduced. You can adjust afterglow to make nice sharp black/white
transitions. It also offers black and
white compression. One thing that can also improve the burn cell response
(especially during run/stop) is to 
parallel two 2 uf 250Vdc film capacitors accross the two existing burn cell
network caps. In some cases, 
defeating the Burn AGC will help. Another "drift" problem we had was
improved by moving some air conditioning 
outlets away from the Rank, and then making sure that the thermostats were
not being tweaked.

Craig Nichols
Todd-AO