[Ether]

500 ma seems way too high. You might even have damaged the opto-isolator's emitter.

I've never been able to find a Victor schematic, but the datasheet for the Jag's opto-isolator says it has an absolute maximum continuous current rating of 60 ma for the input.

The cable I am using for my test equipment here delivers about 5.6 ma to the Victor during the pulse, and it works fine.

Can you post a picture of your scope's current waveform?