Michael A. Terrell schrieb:

80's vintage German printing equipment (offset press industry) uses a video
plug-in card (made by the manufacturer of this equipment) to generate
parameter display for the operator. The display is a standard baseband video
tube monitor. (It is possible, being German and sold in the USA market, that
the video may be NTSC or PAL.)

If it's monochrome, we don't need to talk about NTSC or PAL and their
particular color carrier frequencies...

What frequency crystal should I be looking for?

Mono video used 15,750 Hz for horizontal sweep.

In Europe, especially Germany, horizontal frequency was 15.625 kHz and
vertical frequency 50 Hz in those days.

As others have already suggested, supply a reasonable clock to it,
measure the sync outputs and then change the frequency accordingly.
Chances are good that it's a standard and even frequency, like (for
example) 16 MHz.

Tilmann