[GreenKeys] 28ASR with slow release relay in LESU

Fri Oct 6 12:22:53 EDT 2023

John,

Glad to hear you solved your problem.

I have a M28ASR that someone bypassed the polar relay and added a fixed 
series resistor to the loop.  But I want to use it with TU (HAL ST-6000) 
that has a fixed series resistor in the loop, so I need to dig into the 
LESU and try to return it to the original wiring.

Anytime you use a polar relay, you need to be aware of the polarity, 
since the main coil has to have the opposite polarity of the bias coil.

You said "selector magnets don't care about polarity".  That is true of 
Teletype Corp machines, but all of the Kleinschmidt machines (except for 
the original TT-4) are polarity sensitive due to a bias winding within 
the selector magnet.

The MITE machines used an internal selector magnet driver that was 
polarity sensitive, but they added a bridge rectifier in front of it, so 
loop polarity was not a problem.  (I've been thinking of adding a bridge 
rectifier in front of my KLI machines so as not t o have polarity issues.)

Have fun,

Duncan
K2OEQ

On 05-Oct-23 22:59, John, W9DDD wrote:
> New subject line:  How to waste two weeks for not reading carefully.
>
> I've never had a 28 before where I used the polar relay in the LESU.  
> I think the KSR floor cabinet which also contained the LESU came out 
> of a service that didn't use polar relays.  The other gear was a 28 
> KSR and 28RO which were in skintight rack mount cabinets and didn't 
> have any LESU.  Fast forward to this century. I removed the polar 
> stuff from the KSR I got since that's the way I remember using them 
> before (or maybe it was already gone?) .
>
> The 28 ASR I got, thanks to Nick for transportation, came with a polar 
> relay.  Unfortunately it has a desirable feature which I wanted to 
> keep and means keeping the polar relay.  It involved the 
> aforementioned slow release relay.
>
> So my problem was the printer ran open in all but the K-T position.  
> In that position the SR relay is operated.The keyboard and printer are 
> in effect are switched to a local loop of their own.  That allows you 
> to punch tape and see it on the printer.  So my futile efforts 
> revolved around the relay.  It is connected to the space contact of 
> the polar relay so that if you start getting signals from the line it 
> switches the printer and keyboard back to the signal line.
>
> I spent a lot of time figuring out how to test all the wiring 
> connections without having to turn the LESU upside down. Yes the polar 
> relay is getting 60 mA line current and 30 mA bias current so on and 
> so forth.  Eventually the conclusion was the polar relay has to be 
> bad.  Out comes the 314B version and in goes another. Nuts that didn't 
> work.  Tried about 5 other 255 relays, still doesn't fix the problem.  
> Decided to try adjusting one of the 255s.  Should be good now?  Well 
> no!  Seems like something is fighting the 60 mA side.  Could the line 
> current be of the wrong polarity?  Never was important before 
> (selector magnets don't care about polarity).  Don't ever remember 
> seeing anything about correct polarity in documents.
>
> Well swapped the wiring on the line (loop) wires and son of a gun it 
> fired right up and worked.  The line-test switch tipped me off when I 
> noticed things worked right in test.  To be fair there were other 
> problems at the beginning. I guess all the flipping of switches, 
> plugging and unplugging things along the way took care of dirty 
> contacts that may have been causing the other problems? Nothing like 
> trying to analyze with changing symptoms.
>
> Went and looked at a schematic for a 28 ASR and darned if it doesn't 
> show C5 as being +.
>
> Another joyous moment in this pursuit is that I discovered that one of 
> the 314Bs was a leaker and I now need to clean the polar relay shelf.  
> (the 314Bs are going into zip lock bags.)
>
>
> ---
> ----
> You said "tomorrow" yesterday.
>
> The above comments or recommendations are SWAG. Use at your own risk.
> John, W9DDD
>
> On 9/12/2023 10:50 PM, John, W9DDD wrote:
>> My ASR has a slow release relay in it. It's coil is fired by the 
>> space contact of the line relay (other stuff in there too depending 
>> on the position of the K-KT-T switch).
>>
>> It's an LESU15
>>
>> https://navy-radio.com/manuals/tty/wd/pc/3298wd-iss12-6402.pdf
>>
>> Does anyone know exactly how this supposed to work.  It appears to be 
>> intended to allow you to get local copy during tape punching if there 
>> is no signal line activity and you're in the K-T position.
>>
>> So I'd expect to be able to punch tape and get copy on the printer of 
>> what's being punches with no problem when the Line-Test switch is in 
>> Test position.  Sometime it works that way and other not. Sometimes 
>> it decides it will work with the switch in the Line position and not 
>> have a line connected.
>>
>> I'm expecting a dirty contact in either the slow release relay or the 
>> switch and I'll eventually  go there, but I'd like to have a better 
>> understanding of what's going on before having the machine torn apart 
>> for a long period of time.  It'd be nice to figure out how to test it 
>> before putting keyboard and printer back in.
>>
>> May I assume contact cleaner works on relay contacts?  I've only used 
>> it on wafer switches and potentiometers in a previous life. Maybe 
>> that should be my first approach?  Back to the parts illustrations to 
>> see if I can get to the needed places with minimal tearing apart of 
>> things.
>>
>>
>
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