A poltergeist in my machine?
elson at pico-systems.com
Tue Sep 8 11:21:55 CDT 2015
On 09/08/2015 05:53 AM, Noel Chiappa wrote:
> My current best guess, after sleeping on it, relates to the fact that the
> 'magic' pin was an output from a delay line. Delay lines, in that era, were
> apparently potted confections of inductors and capacitors. So maybe the extra
> current drain with the probe on somehow affected one (or more) of the
> capacitors in the delay line? A total WAG, but it's very mysterious!
Most potted delay lines are made the same way. You take a
piece of aluminum foil-coated paper and roll it into a
tube. You then wind extremely fine magnet wire onto the
tube. The foil is a ground plane, and one of the
distributed capacitor plates. The wire is the distributed
inductor and the other capacitor "plate". This technology
was used in the first color TVs, and I think pretty much
everybody used the same technology for digital delays.
Well, it could be the delay line is going bad.
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