[Elecraft] power fluctuation on transmit

[John Lamoreaux]

Don,

Thanks much for the help.  I hope the problem is now fixed.

I learned a lot in the process, both about the inner workings of the  
K2 and, more importantly, about troubleshooting intermittent problems.

The culprit (hopefully the only one) was a poorly soldered connection  
on RFC1 in the T-R Switch, the lead that connects to C107 and D1.

Thanks again and 73.

John N8ELR





On May 5, 2007, at 5:25 PM, Don Wilhelm wrote:

> John,
>
> That certainly sounds like the behavior of an unsoldered connection.
>
> We can trace everything from end to end through the power control  
> circuits if need be, but for now, look at the schematic and find  
> the VRFDET signal line and check any components that connect to  
> that line. Then check the capacitors that you added to the back of  
> the control board for proper placement and good soldering.  The  
> VPWR and VALC signals are also involved in the power control circuits.
>
> Do you have the basic K2 or do you have the KPA100 attached?  How  
> about a KAT2 or KAT100?  Those add circuitry to the power control  
> loop.
>
> 73,
> Don W3FPR
>
> John Lamoreaux wrote:
>> I'm hoping someone can point me in the right direction for  
>> starting to troubleshoot a K2 (no options installed).
>> I was in the middle of a QSO yesterday, when my power output  
>> started fluctuating.  Up to this point, I've had no troubles since  
>> I finished building the rig.  It may not be relevant, but I had  
>> just installed a new run of coax.  The antenna's SWR showed fine  
>> on my antenna analyzer and on another rig, though.
>> Here's the situation now.  Receive works fine.  When I try to  
>> transmit, however, the power out jumps all over the place, way up  
>> or way down, sometimes giving me a high current warning.  The  
>> current being drawn is also jumping all over the place.
>> It is not being caused by a mismatched antenna.  The same happens  
>> into a dummy load.  A meter connected to the dummy load, by the  
>> way, shows that the actual power out is also fluctuating.
>> So starting from section 160 of the troubleshooting guide (Power  
>> output fluctuates), I'm not sure where to go next, as the causes  
>> there listed are either the antenna or build errors.