Announced 1984
The CX-21 is Epson's 300-baud acoustic coupler from about 1983–84, built to the ITU V.21 standard. It connects to the computer's RS-232 port through a DB25 connector, runs from a 4-cell NiCd pack or a DC adapter, and was made to go with Epson portables such as the PX-8 and HX-20.
I couldn't find a manual or schematic for it online, so I'm documenting what I learn from tracing and measuring my own unit. The write-ups, board photos and any documents I find are collected below.
October 3, 2026 · Repair
The device I bought from eBay had its battery removed but unfortunately too late. The battery leaked through the wires, through the connector to the pcb underneath.I tried to unsolder and replace the connector but the old connector came out together with the hole plating. The two images show CN3 after the failed attempt to…
October 3, 2026 · Repair
No manual or schematic for Epson’s CX-21 acoustic coupler seems to exist online, so I traced the board, measured it and got it working. Chips, power system, the low-battery latch, testing without a phone line, and V.21 frequencies.
