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power fluctuation on transmit

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John Lamoreaux

power fluctuation on transmit

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.

Any thoughts?

Thanks,
John / N8ELR

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Don Wilhelm-3

Re: power fluctuation on transmit

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.
>

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John Lamoreaux

Re: power fluctuation on transmit

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.