I have the engineering prints in the LA 36 Decwriter II LA36 (MPC5) sheet 5 of 8 shows 20 ma RECIEVE on J3 pin 7(+) and Pin 3(-) bridged by a 3.3 volt zener D4 746A feeding a 4N26 (E43) opto-isolator which drives a MXAA05 (Q4) driver transitor which has its collector on J4 pin 2 "S.I." (serial in) 20 ma TRANSMIT is on J3 Pin 5(+) and Pin 2(-). These pins are bridged by a 1N4004 diode D6. This diode also is parallel to the emitter/collector of Q2, an A05. which is driven by another 4N26 opto-isolator (E47). S.O. is J4 pin 4. It is driven by a 7404 inverter (E62)-(Input is 7404 pin 3 connected to the diode cathode of the opto-isolator, output is 7404 pin 4, which connects directly to J4 pin 4, "S.O." serial out) Sincerely Larry Truthan In reply to: Message: 29 Date: Thu, 26 Dec 2002 09:39:19 -0700 From: Kevin Handy <kth(a)srv.net> To: cctalk(a)classiccmp.org Subject: Re: DEC LA36