[Elecraft] K3: Added protection for RS-232 port

[Pete Smith]

Don, I have read several reports on this list of RS-232 failures 
(probably implicating U1 on the KIO3A) apparently due to induced 
voltage.  My comment was based more on my having used radios with serial 
ports for some 15 years and never had any problem with the ports, 
despite leaving serial cables connected all the time.  Elecraft advised 
me always to disconnect any cable from the RS-232 port on my K3 when not 
in use, from which I inferred fragility.

Anyway, the point is that I'm ready to add some protection, if I can 
figure out how to do it.

73, Pete N4ZR

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On 7/18/2010 10:31 PM, Don Wilhelm wrote:
> Pete,
>
> I am not certain why you believe the K3 RS-232 port to be "fragile".  
> I have not seen a large number of failures identified on this reflector.
> There have been quite a number of users who have had problems with USB 
> to RS-232 adapters, but that is not a failure of the K3 RS-232 port.
>
> Can you give me some examples of RS-232 port failures on the K3?
>
> 73,
> Don W3FPR
>
> Pete Smith wrote:
>> I've been thinking about how one might go about adding some 
>> protection for the apparently fragile (and expensive) RS-232 port on 
>> the K3.  It might be possible, if the components were small enough, 
>> to add them on the KIO3 I/O daughterboard, or perhaps on a little 
>> external board mounted at the port.
>>
>> But the question is, what components?  I have seen small gas tube 
>> units, but suspect that by the time the potential reaches 90 volts or 
>> so and the tube flashes over, the RS-232 transceiver is probably 
>> toast anyway.  Would it be feasible to use fast diodes to shunt the 
>> data lines to ground at .7 volts or so, or would that introduce other 
>> problems (stray capacitance, etc.)?  Anything else that might make 
>> sense?
>>
>
>