[GreenKeys] 28ASR with slow release relay in LESU

[John, W9DDD]

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.)


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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.
>
>