W2 Issue

[NZ0T]

My W2 wattmeter suddenly stopped working properly this morning along with
that dreaded smoke smell.  The smell came from the 2KW sensor unit and upon
inspection R22 which is a 1K in the sense circuit is burned.  Of course
it's surface mount but I think I can replace it OK.  If not with another
surface mount I could possibly be able to mount a leaded resistor.  I was
operating at 100 watts on 20 meters into a low SWR when this happened.  Has
anyone else had this happen?  What could have caused this?  I have also
contacted Elecraft tech support about this but I know there are plenty of
experts on this forum too!

73, Bill NZ0T
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[Elecraft mailing list]

Bill;

R22 in the sensors is a sense resistor that tells the controller which sensor is attached. It is a very low stress part that sees at most 5 volts at very low current. R22 is different for each sensor - the values shown in the schematic are not necessarily correct. Also, these are precision 1% resistors. With that in mind, the values are:
2KW HF Sensor, R22 is a 2K ohm 1% SMT resistor.
200W HF Sensor, R22 is a 1KW 1% SMT resistor.
200W VHF Sensor, R22 is a 4.7K 1% SMT resistor.

We need to be careful what we might plug the sensor cable into. The standard box would not stress the resistor to the degree that the resistor blew, especially since that connector also has a ground attached as well. If it were to be plugged into something like an ethernet adapter, I would expect the sensor not to survive since those pins connect to entirely different signals with different characteristics.

73,
Jack, W6FB

> On May 20, 2021, at 6:12 AM, William Carpenter <[hidden email]> wrote:
>
> My W2 wattmeter suddenly stopped working properly this morning along with
> that dreaded smoke smell.  The smell came from the 2KW sensor unit and upon
> inspection R22 which is a 1K in the sense circuit is burned.  Of course
> it's surface mount but I think I can replace it OK.  If not with another
> surface mount I could possibly be able to mount a leaded resistor.  I was
> operating at 100 watts on 20 meters into a low SWR when this happened.  Has
> anyone else had this happen?  What could have caused this?  I have also
> contacted Elecraft tech support about this but I know there are plenty of
> experts on this forum too!
>
> 73, Bill NZ0T
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

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