Vectorbeam monitor issues

Hello, I'm working on a Vectorbeam monitor on which I've replaced about 90%
of the components. This monitor is the "discrete" version with the HV
components on the monitor PCB. It also uses the older part numbers.

Currently the screen is blank, but I'm not sure if it's a problem with the
intensity circuit or a legitimate spot killing. Jumpering Q2 (labled Q24
on my board) causes the picture to appear and reveals that the top half of
the image is missing. All transistors have been replaced.

I should also mention that this monitor has a 7409 at IC7 (labeled U6 on my
board) instead of the 7406 referenced in every document and schematic that
I've seen. There are diodes between pins 1 and 8 and 3 and 8 as seen
here<https://lh3.googleusercontent.com/-aQ9D82rvVr4/UVGOweZsPXI/AAAAAAAAKBk/E1w6AkFky-g/s895/IMG_0007.JPG>.
I've replaced the 7409 and the diodes with new ones, exactly as they were.
The symptoms were the same before and after.

I'd appreciate any insights in understanding if one problem is related to
the other, and how to narrow down the fault(s). Thanks,

Carlos

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Received on Tue Mar 26 08:15:01 2013