RCA 1861, NTSC and a DEC VR-201

From: Allison J Parent <allisonp_at_world.std.com>
Date: Fri Sep 24 17:47:19 1999

<In any case, if there was no other problem, feeding it a mistimed signal
<would most likely result in something on the screen - maybe not locked,
<probably not centred. But there would be _something_.

Therein lies the problem.

First the levels form most of the 1861 based designs are poor or sloppy.
The front and back porches are a bit wide. Likely the problem will be
solved when the said cosmac get's it's circuit fixed.

FYI: I have a cosmac design that has the 1861, the driver for the video
circuit was an emitter follower with a series resistor and no load to
ground. When hooled to a hign impedence input monitor (or with with the
75ohm load switched off) it produced no useable output. The fix was chnge
the output stated to have the correct DC offset and self completing. This
in the end was not a VR201 <or any other monitor> problem just a design that
deliberately minimized cost/components with attendant side effects.

Received on Fri Sep 24 1999 - 17:47:19 BST

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