My faithful 3585a has developed a problem. When a BNC cable is connected to either the 50/75 ohm or 1 megohm input and the cable shield is connected to ground contact of another instrument or the ground contact from a wall outlet, spikes walk across the screen. These spikes are about 20dBm above the noise floor.
If I set the instrument to its default settings, I see the spikes walk across the screen. If I save the waveform to B (where it no longer walks), I count 24 spikes. On many start-stop frequency settings I see the same count of spikes. However, on some I see 48 spikes; e.g. a start frequency of 1MHz and a stop of 2MHz.
Anyone have a suggestion of how to diagnose and repair this problem?
Can the work be done without extender boards?
Thanks,
Gordon, KA2NLM
