[GreenKeys] M28ASR Strange Loop issue...found?

Sun Dec 11 19:46:32 EST 2022

Deoxit is typically used as a lubricant to reduce contact fretting (
https://en.wikipedia.org/wiki/Fretting#Fretting_electrical/electronic_connectors[7]).
Fretting results in a contact resistance increase when currents and
voltages are low. Different contact materials develop resistance increases
differently over time. I worked on a project that used a lithium coin
cell. The load current was 13 uA. The cell holder was nickel plated as was
the cell. Nickel to nickel is one of the worst combinations for low
current contacts. We had failures resulting in the loss of decryption
keys. Gold and gold is the best.

If these connectors were used in a 60 mA current loop with a high loop
voltage, I would be surprised to find a fretting issue. The arcing as
contacts are opened generally cleans off any corrosion. But if the
contacts have not been energized in a long time, I guess they can just get
dirty, and Deoxit would clean them.

Minimum current ratings on connectors, switches, relays, etc. is an
interesting area. Telephone companies run a "sealing current" to prevent
failures of splices. They run the DC current even on a DSL line that does
not otherwise need loop current.

Harold
https://w6iwi.org

On Sun, December 11, 2022 5:01 pm, Paul Wills wrote:
> The contact cleaner is the only substance I found that actually does
> what it says on the container.Â  I'm impressed.
>
> I read about it on a Hickok tube tester restoration site.
>
> PDW
>
> On 12/11/2022 6:07 PM, John W9DDD wrote:
>> For some strange reason I've never heard of DeoxiT.  To my surprise
>> Microcenter shows about 30 products with a DeoxiT search.  I see a mini
>> spray can or a 25ml liquid with needle dispenser that look interesting.
>> I wonder if the flux they have would be useful for some of the old wires
>> that have gotten some corrosion.
>>
>> John, W9DDD
>>
>>
>>> On Dec 11, 2022, at 4:24 PM, W2HX <w2hx at w2hx.com> wrote:
>>>
>>> One bit of good news. Nick and others had suggested that I spray some
>>> deoxit into the RJ jack and work it with a plug. I can now report that
>>> the RJ jack is now properly "normalling" when the plug is removed! I
>>> tried to work it without deoxit and it didn't work. The deoxit was the
>>> trick. Thanks Nick et., al. for the suggestion!
>>>
>>>
>>> 73 Eugene W2HX
>>> Subscribe to my Youtube Channel: https://www.youtube.com/@w2hx/videos
>>>
>>>
>>> -----Original Message-----
>>> From: W2HX
>>> Sent: Sunday, December 4, 2022 9:35 PM
>>> To: Greenkeys <greenkeys at mailman.qth.net>
>>> Subject: M28ASR Strange Loop issue...found?
>>>
>>> Ok everyone. I've got lots of updated information on my issue. To
>>> recap, this ASR has been running very well for the last 15 years.
>>> Recently the loop-driven LPR (sits on the keyboard contacts) recently
>>> stopped working in the way it has for all these years.  I've spent the
>>> last week and have poured dozens of hours into understanding how my ASR
>>> is set up. It was set up by Jack Hart (sk) who knew what he was doing.
>>> Only problem is I didn't know what he was doing hihi.
>>>
>>> Thanks to Nick, K4NYW who saved some of the materials from Jack, and
>>> thanks to me for never deleting emails, I was able to find some
>>> original correspondence with Jack dating back to July of 2005 when I
>>> first bought the machine from him. I studied the diagram for the WU
>>> 9797 LESU ad nauseum and learned a LOT.
>>>
>>> Here is how my electrical is configured.
>>>
>>> EXTERNAL LOOP (TRAFFIC) ---> KEYBOARD ---> TD ---> LPR (ON) ---> POLAR
>>> RELAY INTERNAL LOOP 1 (KEYED FROM POLAR RELAY) ---> PAGE PRINTER
>>> INTERNAL LOOP 2 (NOT KEYED, ALWAYS MARKING) --> LPR (OFF)
>>>
>>> I have a DPDT switch mounted beneath the ASR that connects the LPR to
>>> one of two loops, either the internal loop (LPR OFF) and the external
>>> loop (LPR ON). In this way, when I don't want to punch tape from the
>>> external line, (OFF) it is connected to the internal loop and keeps the
>>> LPR in mark-hold (closed) at all times.
>>>
>>> The problem (previously described poorly) was that when the LPR was off
>>> (mark-holding, LOOP 1) it would run open. I spent days working on
>>> figuring this out. I found that when I plugged an ammeter into the RJ
>>> (reperf jack) it would close the circuit and work properly! This made
>>> no sense because these jacks should be normalling (shorting) when a
>>> plug is removed. But in this case, it seems to be open circuit.
>>>
>>> Ultimately, I must have damaged this jack when I was messing around
>>> learning about the electrical configuration which must have caused this
>>> problem. I wonder if anyone has any thoughts on this? I could attempt
>>> to pull the LESU open it up and repair it. And I probably should but
>>> seems like a bigger project than I'd like to take on at this moment. So
>>> I might just make a shorting plug to do the business.
>>>
>>> In case anyone is interested, here is a video I made on the whole set
>>> up and you can see the problem firsthand. And you can see how the
>>> problem resolves with an ammeter in the RJ jack.
>>>
>>> https://youtu.be/ULO6B07koDM
>>>
>>>
>>> 73 Eugene W2HX
>>> Subscribe to my Youtube Channel: https://www.youtube.com/@w2hx/videos
>>>
>>>
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>>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>>> https://teletype.net/gksearch
>>>>> 2002-to-present greenkeys archive:
>>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>>> 1998-to-2001 greenkeys archive:
>>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>>> http://comcents.com/tty/greenkeyssearch.html
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>> Please help support this email list: http://www.qsl.net/donate.html
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> ______________________________________________________________
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> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:GreenKeys at mailman.qth.net
>
>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>> https://teletype.net/gksearch
>>>> 2002-to-present greenkeys archive:
>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>> 1998-to-2001 greenkeys archive:
>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>> http://comcents.com/tty/greenkeyssearch.html
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to harold at w6iwi.org
>

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