One op amp drives the meter and another op amp drives the interface, they both get their input from the same point so since the meter works you can ignore the input as being bad, VR4 calibrates the interface op amp. I would disconnect the interface and measure the pin on the back to make sure it is not the interface dragging it down. See if your line swings properly and adjust VR4 for the correct max voltage.

------- Original Message -------
On Sunday, January 29th, 2023 at 1:28 PM, Stephan Greene via AMSAT-BB <amsat-bb@amsat.org> wrote:

Elevation control for my vintage G5400 controller has gone wonky. The front panel meter displays correctly, but the voltage on the DIN port is low, including after a re-calibration (ERC-M interface, detailed every 5-10 deg). Result is the antennas get driven to too high an elevation. Same results with CSN SAT interface and a different DIN cable, so it isn't a voltage sensing circuit in the ERC.

I'll be measuring the voltage directly at the cable attachment pins and DIN port on the controller, but the meter reading correctly suggests the problem may be in the box and not the potentiometers out at the rotator. For now, disabled elevation control in SatPC32 so I just have to manage elevation manually.

Other troubleshooting suggestions welcome. Thanks in advance.

73 Steve KS1G