HP97 The journey begins

[teenix]

Hi all,

I got my oscilloscope the other day and have been having a play.

The attached image shows the trace from an active HP-97 display

Yellow - RCD (reset cathode driver to first digit)
Blue - STB (go to next digit cathode strobe)

The bottom 2 are LED segments A and B of the exponent digits just after the RCD pulse.

What I find confusing is the different voltages at the 3rd STB pulse. Most are at around 3V while the larger ones are at 5V and don't appear on all segments for a single digit.

Has anyone played with this in the past and could offer some insight?

cheers

Tony