We have a DTR-8D-1 Series-i Dterm set that is not behaving like other sets on our (SV8100) system.

On most sets pressing the up/down arrow keys when the phone is idle adjusts the LCD contrast (as expected).

On this particular set pressing the up/down arrow keys when the phone is idle adjusts the speaker volume.

I'm not able to find a way to change the LCD contrast on this device. Any thoughts?