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Mk III problem

We have two MkIII turbo machines that are both exibiting a 
similar problem. There is a faint light line on the left side of the 
screen (most apparent with dense negative). On the machine that has a 
pre-store corrector, the line is about .5usec from the left edge, on the 
machine with post store correction, it is 2.3 usec from the edge. The 
difference is because of different timing settings on the store control 
board to compensate for the extra delay of the pre store programer.
	I think I have issolated the problem to the 247 video board. The 
noise blanking pulse has a spike on it that is concurrent with the line. 
the spike looks like crosstalk from another pulse, but I cannot find any 
pulse that is happening at that point in time. It is possible that the 
same signal is being induced on the video and the noise blanking pulse. 
I am farly certain that the problem does not exist before this board, 
and does exist after. As it is happening in both of our Ranks (oops) I 
figured that someone has seen it before. Thanks in advance. Vince.