GTERM25 - DB25 Active SCSI Terminator with diagnostics LEDs

Submitted by GG on Sun, 02/16/2020 - 15:28
Project Status

GTERMActive termination is required to get newer high performance drives working on vintage computers. Unfortunately both the Amiga and older Apple computers use a DB25 SCSI connector which makes finding a suitable terminator quite difficult. GTERM25 solves this problem providing a high performance active terminator with a DB25 connector and SCSI diagnostic LEDs.

The previous version of the active terminator used the hard to find UC5603 SCSI terminator IC from Unitrode/TI. For the new B00 version we opted for a much more common 2.85V regulator paired with 110ohm 1% resistors. A total of 18 termination resistors are necessary to terminate a 8-bit SCSI bus like the one on the Amiga, Apple II and early Macs.
The TERM LED makes sure termination power is present. An additional 7404 inverting buffer drives the other three diagnostic LEDs for SEL, REQ and ACK.
The PCB is shaped to fit into a standard DB25 cable shell.

GTERM ShellA3000

Filed under