AT&T Lucent Avaya TN748C Tone Detector Circuit Board Card V5

AT&T Lucent Avaya TN748C Tone Detector Circuit Board Card V5

The TN748C is a Tone Detector circuit board designed for use in AT&T, Lucent, and Avaya DEFINITY PBX telephone systems. Tone detector cards handle the detection of in-band call-progress and DTMF tones across active call paths, enabling the PBX to monitor and respond to dialed digits and signaling events. This is a V5 revision of the TN748C board, carrying multiple rows of DIP and surface-mount ICs across a full-length red PCB with a proprietary dual-row backplane edge connector.

Specifications & What's Included

• Model: TN748C
• Hardware Version: V5
• Type: Tone Detector Circuit Board / Card
• Form Factor: Single-slot PBX circuit card with proprietary backplane edge connector (dual-row)
• Compatible Systems: AT&T / Lucent / Avaya DEFINITY PBX family; Avaya AUDIX voice messaging
• PCB: Full-length red board populated with multiple DIP ICs and surface-mount components
• Faceplate: White plastic single-slot faceplate with printed TN748C label, V5 designation, and barcode
• Card only — no cables or accessories included

Applications

The TN748C Tone Detector card is used in Avaya DEFINITY G1 through G3 series PBX systems and related AUDIX voice messaging platforms. Tone detector resources are consumed by the PBX call-processing software whenever a trunk or station port needs active tone monitoring — for example, during call transfer, conference setup, or automated attendant digit collection. DEFINITY systems allocate tone detector circuits from installed TN748-series cards dynamically across the port network. These cards are a standard component of any DEFINITY cabinet and are regularly needed as spares or replacements in legacy Avaya PBX installations still operating in hospitality, healthcare, education, and enterprise environments.