Old oscilloscope help: ideas sought

[der Mouse]

I know, bad form to follow up to myself....

> [...'scope which doesn't seem to have the beam on-screen...]

...I turned out to be in luck.

On closer examination, this 'scope has a bank of screw terminals which
are labeled (in black-on-dark-brown, not obvious except on close
inspection) as being suitable for jumpering in certain ways to get the
X and Y deflection plates as coming direct from inputs or coming from
the X and Y deflection amplifier circuitry.  I removed the insulator
panel on which these terminals are mounted, and it is clear that four
of the terminals go directly to the deflection plates (two for each
axis), with a resistor (4.7M) hardwired from there to the
deflection-amplifier terminals.  (The direct-input terminals are
capacitor-coupled to the plates if the jumpers are in the direct-input
positions; if the jumpers are in the amplifier-fed positions, they
short out these resistors, with the direct-input terminals doing
nothing at all.)

So I removed the jumpers entirely and, using alligator clip leads,
grounded both X deflector plates (to the chassis, that being where all
other grounds go).  Voila, I can find the trace!  (Well, spot, under
the circumstances.)  Using a voltmeter on the amplifier-output
terminals indicates that one is driving about +100V and the other about
+400V (of course, these may be reading low because of meter impedance,
but they clearly are nowhere near equal).  Grounding the deflection
plate corresponding to the +400V line and leaving the other alone gives
me a spot near one edge of the display; the other way around and I get
the symptom I wrote about.

So now it's just a matter of tracing circuitry back until I find the
problem.  (Heh.  "Just".)  Sorry to bother everyone when the answer was
right there waiting to be discovered all the time.

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