[GreenKeys] RS232-Current loop converter troubleshooting

[drlegendre .]

"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."

Re-reading your post, it also sounds like the large power resistor may have
changed value (upward) or opened up entirely. What you describe sounds like
you're seeing a high-impedance voltage on pins 5 & 6.. which could be
either due to a bad resistor or again, an optocoupler. Check the power
resistor value, and make sure it hasn't de-soldered itself from the circuit
due to overhearing.

FYI I used one of those 25W Dale power resistors in the gold anodized,
finned aluminum case. This is in turn mounted to the metal enclosure (with
HS compound) which is more than adequate to dissipate the heat.

On Mon, Jan 18, 2016 at 11:20 AM, Sarah Autumn <neverether at gmail.com> wrote:

> Thanks, I have some spare optocouplers, so I'll try replacing them.
>
> On Sun, Jan 17, 2016 at 9:44 PM, drlegendre . <drlegendre at gmail.com>
> wrote:
>
>> "..worked fine at first.."
>>
>> In other words, some part(s) broke down during operation. There aren't
>> too many things to break in this design, save the two optocouplers - so I'd
>> look at those, first.
>>
>> My build broke early on as well, but in that case, it was due to nicked
>> (solid-core) wire that broke off of a soldered connection. I used salvaged
>> telco wire, and that stuff is pretty fragile when it takes a nick. For the
>> second-round repair, I used a hot stripper - so no damage to the wiring.
>>
>> On Sun, Jan 17, 2016 at 9:34 PM, Sarah Autumn <neverether at gmail.com>
>> wrote:
>>
>>> 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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>
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