[GreenKeys] Current loop not providing (enough) current

[epvgk at limpoc.com]

On Thu, Sep 26, 2019 at 11:05:53PM -0400, Ralph Mowery wrote:
> Ok, this points to the PC board doing something wrong.  
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> I don’t have the schematic for that board to help any more at this time.    You should be able to short out or just take the PC board out of the circuit and the teletype should type from the keyboard.   Just remember what I mentioned about the coils could be what I call out of phase and the wires on one may need to be reversed.
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> I don’ tknow if a transistor or IC (optical  isolator) is being used to switch the loop off and on.  Whatever it is, is probably bad or whatever driving it is not driving it hard enough to put it into full conduction.
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It's an optoisolator, but if it were presenting enough resistance to drop his loop 
to 30mA from 60mA at 120VDC it would literally ignite. 

But anyway I thought he was already testing this without that board in the circuit at all?
It would definitely be best to remove or short it out to see what changes. 

Another though - I have a bunch of quarter inch plugs/jacks for loop connectors and I've
had those make bad enough contact to cause something like this. 

eric

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> I do not do DMR.  Have no plans for it as of now.  I can operate any band from 80 to 10 meters and even higher ,but you are probably too far away.  
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> I am located in the middle of  North Carolina, where are you  ?
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> Ralph ku4pt
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> From: Zach Zarzycki [mailto:shardsofaperture at gmail.com] 
> Sent: Thursday, September 26, 2019 8:20 PM
> To: Ralph Mowery
> Cc: GreenKeys
> Subject: Re: [GreenKeys] Current loop not providing (enough) current
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> Ok, so the power supply and resistors made 60 ma, when I hook the power supply up to the PC board, drops in half to 30 ma (no teletype on the loop). It was my understanding the polarity into the PC board didn't matter if it was hooked. I'll try to flip them. 
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> But at this point supply to resistor in a loop is 60mA!
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> As an aside, the teletype does measure about 45 ohm.
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