Greetings

I have an early Aim65 (Serial Number AP225) with a R24 value of 1K.

I 'm aware Later Aim65s that part R24 was replaced with 3.3K value.

This after finding a Rockwell Application Note for RS-232 Interface for Aim 65.

my understand the circuit featured in application for optical device does not work.

I build a cute little 20 ma loop to rs-232 prototype conversion board.

I got the Serout section working such that can have AIM65 send character to a PC terminal program as well get characters when you set up a417a418 to $02fd, flipped the switch to TTY and press the space bar on the Aim's key board sends character to the PC terminal program .

I have in the past had my Aim65 connected to a ASR33 TTY terminal.

I'm using a sipex sp232cp chip for Serout section.

Now for the rub ...

For Serin (J1-Y) on the Aim65 .. I probe the signal at R23 at one end I see a good
signal and but at the other end the signal is very tiny in comparison and result there's
tiny signal at Z5- pin5.

I'm wondering if the fix is to replacing that 1k part with 3.3K part.

I check the circuit and appears no other parts were changed.

So I changed R24 resistor from 1 K to 3.3K and now the Ser out signal quit working ..

Simplex 232 that I'm using is getting very hot and over heating.

I had used 1 uf 50 volt electrolytic caps.

I'm planning to replace those caps with .1uf.

Another note important to know the pull resistor to pull up the Ser out from the Aim 65 had a value of 1k
instead of the 3.3K resistor shown in the Rockwell Application Note for the RS-232 Interface for Aim 65.

I'm wonder if I should can that pull up value from 1K to 3.3K as shown in the app note.

Any comments. ???

Welcome! I think it would be helpful to see a diagram of what you have, and a circuit diagram of your 20ma current loop converter.

Unfortunately I can't help much as I lack relevant experience, but others may have it, and the problem might be a straightforward electronics question, at root.