That sounds as if it could have been a Computer Accessories Corporation Mac Data Display A342, a 512x342 external LCD device (circa 1987) for the Macintosh to SE and any transmissive overhead projector.
Before I was reminded by Scott, I had forgotten that that device uses a DB-9 out, designed to pass through the security slot. However, the connector has no particular virtue in itself if the separately-powered (9VDC) display module (which contains all of the electronics to process the signal 'picked off' from the power/sweep board to logic board loom) is not included in the deal.
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Before I was reminded by Scott, I had forgotten that that device uses a DB-9 out, designed to pass through the security slot. However, the connector has no particular virtue in itself if the separately-powered (9VDC) display module (which contains all of the electronics to process the signal 'picked off' from the power/sweep board to logic board loom) is not included in the deal.
de