K2 Low Power Out / Hi Current

[JeremyJones]

I'm trying to complete the stage 3 transmitter alignment on my K2 and have run into a bit of a snag.  The 40M check looks good according to the built in power meter, however with an external watt meter connected to a dummy load, I am getting less than 1W on the with the K2 set at 2W, and about 2W when set for 10W.  Moving on to 80M at 2W I get a high current warning.

I checked the voltages on Q5, Q6, Q7 and Q8 as per the manual trouble shooting.  All of the collectors are at 15.12V, and all emitters and bases are at 0v.  My transformers look like the diagrams and have the proper number of turns.  What else should I be looking at?

Thanks
Jeremy
VA3ZTF

[Don Wilhelm-4]

Jeremy,

The problem of HiCur coupled with low power output is usually associated
with a problem either in T4 or the Low Pass Filter.

Check all the capacitors in the Low Pass Filter for proper values and
count the turns on the toroids.  Count only the turns passing through
the center of the core.  It is easy to put an extra turn on the toroids,
and the result is a HiCur message along with low power output.

73,
Don W3FPR

On 3/5/2013 7:58 PM, JeremyJones wrote:
> I'm trying to complete the stage 3 transmitter alignment on my K2 and have
> run into a bit of a snag.  The 40M check looks good according to the built
> in power meter, however with an external watt meter connected to a dummy
> load, I am getting less than 1W on the with the K2 set at 2W, and about 2W
> when set for 10W.  Moving on to 80M at 2W I get a high current warning.
>

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[JeremyJones]

Hi Don,

The capacitors all look good, and I found one issue with a toroid and corrected it, but the issue remains.  T4 is wound with proper number of turns, but wires do overlap some instead of being stacked neatly.  Not sure if this could cause an issue or not.  T4 is also standing off the board a bit, rather than being snug to the screws underneath.

Jeremy
VA3ZTF

[Don Wilhelm-4]

Jeremy,

T4 being off the board should not make any difference.  Are you
operating into a dummy load that is 50 ohms pure resistive, or are you
operating into an antenna?  The base K2 needs to operate into a 50 ohm
resistive load for good power control and a proper impedance.

If you are operating into an antenna, use your antenna analyzer and
adjust your tuner for a 50 +/- j0 impedance.

73,
Don W3FPR


On 3/5/2013 9:08 PM, JeremyJones wrote:

> Hi Don,
>
> The capacitors all look good, and I found one issue with a toroid and
> corrected it, but the issue remains.  T4 is wound with proper number of
> turns, but wires do overlap some instead of being stacked neatly.  Not sure
> if this could cause an issue or not.  T4 is also standing off the board a
> bit, rather than being snug to the screws underneath.
>
> Jeremy
> VA3ZTF
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-Low-Power-Out-Hi-Current-tp7570850p7570857.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
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[Don Wilhelm-4]

Jeremy,

A high SWR will cause that behavior.
Make certain the coax you are using is good.  Remove it from the K2 end
and check with an antenna analyzer if possible.
If you cannot do that, look at the SWR registered on the wattmeter - if
it is 1:1, remove the wattmeter and connect that coax to the dummy load
(no wattmeter).

73,
Don W3FPR

On 3/5/2013 9:08 PM, JeremyJones wrote:

> Hi Don,
>
> The capacitors all look good, and I found one issue with a toroid and
> corrected it, but the issue remains.  T4 is wound with proper number of
> turns, but wires do overlap some instead of being stacked neatly.  Not sure
> if this could cause an issue or not.  T4 is also standing off the board a
> bit, rather than being snug to the screws underneath.
>
> Jeremy
> VA3ZTF
>

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[JeremyJones]

Looks like a bad coax was indeed causing the high current issue.  I've resolved that, but I'm still show no power out on the external watt meter, while the internal is reading 2.4.

Jeremy
VA3ZTF

[Don Wilhelm-4]

Jeremy,

What range is your external wattmeter set for?  If it is 100 watts or
200 watts, you will probably not get any deflection at 2.4 watts.

When the load is 50+j0 ohms, you can rely on the K2 display.
I suggest removing the external wattmeter and using the display.

73,
Don W3FPR

On 3/6/2013 3:55 PM, JeremyJones wrote:
> Looks like a bad coax was indeed causing the high current issue.  I've
> resolved that, but I'm still show no power out on the external watt meter,
> while the internal is reading 2.4.
>
> Jeremy
> VA3ZTF
>

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[JeremyJones]

The watt meter has a 5, 15, 50, 100W ranges, and I was using the 15 and 5 to try and get measurements.  Carrying on with calibration using the internal meter yielded the expected results.  I may actually be able get this on the air tonight!

Thanks for the help,
Jeremy
VA3ZTF

[Don Wilhelm-4]

Jeremy and all,  the external wattmeter reading has to overcome the
diode drop in the wattmeter before it will provide deflection.  At low
power levels it may show no response until the power is great enough for
the diodes to conduct.
The full scale reading of the wattmeter may be correct, but at low power
levels there is a certain 'threshold' below which some meters will show
no power output (regardless of the range).

I am glad to hear that you now have the bandpass filters peaked.

73,
Don W3FPR

On 3/6/2013 5:17 PM, JeremyJones wrote:

> The watt meter has a 5, 15, 50, 100W ranges, and I was using the 15 and 5 to
> try and get measurements.  Carrying on with calibration using the internal
> meter yielded the expected results.  I may actually be able get this on the
> air tonight!
>
> Thanks for the help,
> Jeremy
> VA3ZTF
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-Low-Power-Out-Hi-Current-tp7570850p7570907.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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[JeremyJones]

Don,

I suspected something might be wrong with the watt meter, as it was borrowed from work and had not been used in a while.  
I was able to listen to quite a few signals last night, however I wasn't able to make any contacts.  I brought my radio into work and tested it on a Rhode and Schwartz FSH8 with power sensor to double check the original power meter and the radio.  Even with the radio set to 10W I was showing no power out.

I don't have the schematic handy, but can I do some signal tracing from between where the K2 takes its power reading and the BNC output?

[Don Wilhelm-4]

Jeremy,

Strange problem.

The K2 RF power detector consists of voltage divider R67 and R68 and
diode D9.  One end of R67 is connected directly to the BNC center
conductor.  That means your problem is quite a mystery.  Could it be a
bad coax or a faulty (or not soldered) BNC connector.  The only other
possibility I can think of is a broken PC trace, but those traces are
quite large.

If there is not a proper connection to the dummy load, the normal result
is a HiCur message with the power set to a high level because the K2 is
operating into an open circuit.

73,
Don W3FPR

On 3/7/2013 8:04 AM, JeremyJones wrote:

> Don,
>
> I suspected something might be wrong with the watt meter, as it was borrowed
> from work and had not been used in a while.
> I was able to listen to quite a few signals last night, however I wasn't
> able to make any contacts.  I brought my radio into work and tested it on a
> Rhode and Schwartz FSH8 with power sensor to double check the original power
> meter and the radio.  Even with the radio set to 10W I was showing no power
> out.
>
> I don't have the schematic handy, but can I do some signal tracing from
> between where the K2 takes its power reading and the BNC output?
>

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[JeremyJones]

So, I have learned another lesson on paying attention to details.  Seems the analog watt meter I was using is only rated as low as 20mhz, and the digital Rhode and Schwartz actually had a 200Mhz sensor on it.  No wonder the readings were bad.

I did go back to the analog meter on 15M, 12M, and 10M.  At 10W on the radio I was showing 3.5W on the analog meter.  It has a correction factor of +40% for 20Mhz, so that would be a reading of 5W, about half of what it should be.  

I did the signal tracing from the manual.  Some values were considerably low, while other were quite close.  
Xmit mixer out read .002 vice .016
Buffer Output was .107 vice .200.
Predriver Output .65 vice .120
Driver input .008 vice .026