I don't know KX-TA824 system at all, but KX-TE824 supports PTs only at Jack01 - Jack16 (Jack17 - Jack24 support only SLT-phones). 3) Cabling distance can affect, because of KX-T7730 doesn't have LCD or Keyboard backlight. So try to connect T7737 directly to PBX-port. Upvote ...