A differential voltage probe was used. There is no true “ground” side of a differential voltage probe that must be connected to earth ground. The “negative” side of the differential probe was connected to the negative DC bus of the drive. You are correct that many small HP drives do not have easy access to the DC bus. The ACH580-01 series drives R1 - R3 frame do not have access to the negative side of the DC bus by the power terminals, but do have access to recessed test point eye loop located above the control board (R1 and R2 frame) or to the left of the control board (R3 frame). If you did connect the differential voltage probes “backwards” across the DC bus, most oscilloscopes provide an option to invert or flip the signals on the channel.
These troubleshooting videos are great, I hope there is more to come.
Where did you connect scope probe GND? None of these drives seems to have reference GND accessible.
A differential voltage probe was used. There is no true “ground” side of a differential voltage probe that must be connected to earth ground. The “negative” side of the differential probe was connected to the negative DC bus of the drive. You are correct that many small HP drives do not have easy access to the DC bus. The ACH580-01 series drives R1 - R3 frame do not have access to the negative side of the DC bus by the power terminals, but do have access to recessed test point eye loop located above the control board (R1 and R2 frame) or to the left of the control board (R3 frame). If you did connect the differential voltage probes “backwards” across the DC bus, most oscilloscopes provide an option to invert or flip the signals on the channel.
These videos are perfect for process and troubleshooting. Thank you for uploading these!