[GreenKeys] RS232-Current loop converter troubleshooting

[hwhall at compuserve.com]

That sounds suspiciously like a problem I've seen one or two times. A wire or contact is broken or in poor contact, a high resistance contact, so that it can carry a very small current (milli or micro amps) and show near normal voltage but when more current is demanded, the voltage drop becomes large and the load isn't satisfied. Worst case was broken wire inside an otherwise OK-looking length of zipcord. Took a while to actually believe what the meter was telling me because I "couldn't see anything wrong."
 

 Check all the wires, connectors and related solder joints closely for minute breaks, cold joint, etc.

Wayne
WB4OGM

 

-----Original Message-----
From: Sarah Autumn <neverether at gmail.com>
To: Greenkeys <greenkeys at mailman.qth.net>
Sent: Sun, Jan 17, 2016 10:17 pm
Subject: [GreenKeys] RS232-Current loop converter troubleshooting



Hi all,


I finally got around to building the loop to serial converter that everyone knows and loves (http://www.aetherltd.com/connecting.html). It worked fine at first, but now I'm getting this weird behavior.


When there is no teletype connected, on the pins for the selector magnet (J1 5&6) have voltage. When I connect the teletype to the pins, the voltage drops to almost nothing, and the magnet doesn't operate. If I remove the teletype from pins 5&6, the voltage jumps back up to 100V. When I hook the teletype directly to my loop supply, it runs fine.


I have also tried 2 different power supplies: One is an acoustic coupler modem used for the deaf, and another is a REC-50.


I have checked the values of all my resistors and capacitors. What simple, easy thing am I doing wrong?

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