Rick & Joe,
Thanks for your suggestions, however, all of your mentioned items have
been checked, and I am quite confident that the problem lies inside the box.
I now have a 333 page service manual...that unfortunately is more oriented
towards callibration than troubleshooting...but may lead to some useful
information.

First thing I'd suggest checking on a scope of this vintage is the
power supply bypass capacitors. See if there's excessive AC ripple on
any of the DC supply lines - if so, one of the 'lytic capacitor cans
has probably dried out and gone high-Z. All sorts of interesting
symptoms can occur as a result.

Exact-replacement caps are likely to be impossible to find - you may
very well need to improvise, using a modern 'lytic of equal or greater
capacity and WVDC rating, and some creative wiring and mounting
arrangements to adapt the new cap(s) to the old pinouts.

--
Dave Platt AE6EO
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