Fujitsu HA15B-0001-B052 DSU Data Service Unit V.35 Sync Async Modem

Fujitsu HA15B-0001-B052 DSU Data Service Unit V.35 Sync Async Modem

The Fujitsu HA15B-0001-B052 is a desktop DSU (Data Service Unit) designed for synchronous and asynchronous serial data communications over leased lines. It provides a V.35 primary synchronous interface along with secondary asynchronous and subrate ports, making it suitable for point-to-point digital data circuit applications. The front panel features a rotary test selector and a full array of LED status indicators for monitoring circuit activity and running diagnostics.

Specifications & What's Included

• Manufacturer: Fujitsu
• Model / MPN: HA15B-0001-B052
• Type: DSU (Data Service Unit)
• Primary Sync Interface: V.35 — 34-pin Winchester-style connector (labeled PRI SYNC / V.35 on rear)
• Async Interface: DB-25 connector (labeled ASYNC on rear)
• Subrate Interface: DB-25 connector (labeled PRI SYNC SUBRATE on rear)
• Telco Port: RJ-style jack on rear panel (labeled TELCO)
• Front-panel rotary test selector: positions include DATA, LL, RT, EET, ST (dual-row, inner and outer ring)
• LED status indicators — PRI (SYNC): CS, SD, RD; SEC (ASYNC): SD, RD; PRI (ASYNC): CS, SD, RD; TEST: RT, LL, TS, NS, OS, ER
• Internal DIP switch banks: SW2 (Rate), SW3 (Word/Rate), SW4 (Default Settings) — accessible via hinged top panel
• Form Factor: Desktop / Benchtop
• AC power cord attached (visible in photos)
• Unit only; no additional accessories included

Applications

DSUs like the Fujitsu HA15B-0001-B052 were standard terminating equipment for leased digital data circuits in corporate and government telecommunications networks from the 1980s through the 1990s. A DSU converts the digital data signals from DTE (data terminal equipment — such as a router, multiplexer, or mainframe front-end processor) into the bipolar line signals required by the telco's digital circuit, and vice versa in the receive direction. The V.35 interface was the dominant high-speed synchronous serial standard of that era, widely used to connect routers, X.25 packet assemblers, and IBM SNA front-end processors to leased lines at speeds typically ranging from 56 Kbps to 2 Mbps. The secondary asynchronous and subrate ports on this unit allowed it to support multiplexed or secondary async traffic on the same circuit — a common requirement in multi-drop leased-line networks. This type of equipment was deployed at customer premises (CPE) as the network interface point between the enterprise's data equipment and the telco's digital local loop. Today, standalone DSUs of this generation have largely been replaced by integrated CSU/DSU modules within routers, but units like this remain relevant for legacy network maintenance, IBM SNA environments, and hobbyist or museum restoration of period telecommunications systems.