[GreenKeys] Current Loop to RS-232 Conversion on ASR33

[Teletypeparts]

Rob,

The only thing between the 33 and its output in Line mode is the Line/Local relay and some wires.  If it works in Local then likely nothing was damaged.  

Is the board behind the Line/Local switch vertical with a vertical metal relay on it?  If so its just the tape reader control card that was used with PDP computers.  You need a closure and 15 volts from the computer to run the tape reader in Line mode.  You can check this by seeing if the reader runs in Line mode.  If the extra card is for reader control, it wont run in Line mode without a connection to the computer but will work in Local.  That is unless someone has bypassed the normal wiring.  

Wayne  



-----Original Message-----
From: epvgk <epvgk at limpoc.com>
To: r.jarratt <r.jarratt at computer.org>
Cc: greenkeys <greenkeys at mailman.qth.net>
Sent: Sun, Mar 24, 2013 8:32 pm
Subject: Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33


On Sun, Mar 24, 2013 at 11:44:04PM -0000, Rob Jarratt wrote:
 Yes, I think what you say may be right (although mine does not have a
 telephone panel). But even if you are right and it does have a loop supply
 inside the ASR33 why does it only appear to output about 10mA and then drop
 to the point that it starts to chatter as if it was open? Yet, when in local
 mode it works perfectly, so the current would *appear* to be enough.
 
It's also worth considering that if you did at some point connect more than
ne highish-voltage supply into the loop in series, you may have damaged either
he current loop converter or the tty's solenoid driver? 
eric
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