K2 Problem 12 Watts Out With Power Control Fully CCW

[Joseph Szczubelek]

The build for K2 ser # 5628 has been going well until
I got to the "Alignment and Test Part III"  40 meter
transmitter alignment section.

Problem:

With current set to 2.0 AMPS and the power control
fully CCW I measured 7 watts on an external wattmeter.
The internal wattmeter had NO indication. When I press
the "tune" control with the display set for voltage
and current I see 13.3 volts and 1.88 amps. The
current will start to slowly rise at .02 amps per
second and will reach 2.00 amps in about 10 seconds
and the "HI CURRENT" message will appear with 7 watts
output.

If I set the power to .5 watts the current will start
out at 1.98 amps and the 2.00 amp threshold and "HI
CURRENT" message will appear much quicker - about 1
second. I still get 7 watts of output indicated on an
external wattmeter.

Setting the current to 3.00 amps and the power control
fully CCW I get 12 watts out with 13.0 volts and the
current starting at 2.84 amps creeping up at .02 amps
per second. At around 10 seconds the HI CURRENT
message will appear when 3.0 amps has been reached.

Setting the power to .5 watts will cause the same
thing to happen but HI CURRENT message appears quickly
with 12 watts output.

Additional Info:

The K2 has passed all checks up to this point. I am
using a Heathkit 50 ohm dummy load. Turning the power
control up or down gives the  indication of the
desired power but has no effect. L1 and L2 gives a
nice peak for 40 meters. They were very close if not
right on from the 40 meter receiver test.  Measuring
the resistance at the collectors of finals Q7 and Q8
shows 3.7K for both transistors. The power output is
being controlled by limiting the current not by the
power control. The internal wattmeter gives no
indication on transmit but works as an S meter on
receive.  I am using a 30 amp Ashton switching supply.
It was Sunday evening so I called it a day.


Best,

Joe Szczubelek  -  K9DMV



 
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[Don Wilhelm-3]

Joe,

The initial problem to be solved is that there is no indication of power
output being fed back to the K2 microprocessor.

The most likely source is a bad solder connection and the second most likely
is a misplaced component.

Keep your testing periods short, ignore the high current messages for now,
and proceed as follows:
Start your search at RF Board diode D9 - if all is well at that point, there
will be a DC voltage during transmit periods - how large it is depends on
the amount of RF output, for now just be certain you have a good solid DC
voltage there - anything over a volt or so will indicate that the RF Output
Detector is working.

Next point is on the Control Board - the VFRDET signal which appears at pin
10 of P4 - the DC voltage during transmit should be about the same as you
measured at the cathode of D9.

Lastly, check the VRFDET signal at the microprocessor - U6 pin 2.  The
voltage should be about the same as at P4 pin 10 if R12 is properly in
place.

Let us know where the VRFDET signal path is broken.

73,
Don W3FPR

> -----Original Message-----
>
> The build for K2 ser # 5628 has been going well until
> I got to the "Alignment and Test Part III"  40 meter
> transmitter alignment section.
>
> Problem:
>
> With current set to 2.0 AMPS and the power control
> fully CCW I measured 7 watts on an external wattmeter.
> The internal wattmeter had NO indication. When I press
> the "tune" control with the display set for voltage
> and current I see 13.3 volts and 1.88 amps. The
> current will start to slowly rise at .02 amps per
> second and will reach 2.00 amps in about 10 seconds
> and the "HI CURRENT" message will appear with 7 watts
> output.
>
>

--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.430 / Virus Database: 268.15.6/567 - Release Date: 12/4/2006
7:18 AM

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[Joseph Szczubelek]

With a few helpfull tips from Don Wilhelm - W3FPR I
was able to quickly resolve my K2 power output
problem.

The voltage measured at diode D9 cathode (marked end)
on the RF board was 2.30 volts DC. After R66 (2.7K) it
was 0.0 volts. The microprocessor was NOT getting the
RF output signal via VRFDET. The interal RF output
meter was not indicating any output power. During the
build I installed the RG174 coax at signal "RF" for
the K60XV Rework Eliminator. When soldering the braid
on the other end to L4 the center conductor shorted to
the braid grounding the signal from D9 - operator
error.

Correcting that problem I now get 10 watts out at 2.1
amps on 40 meters with the power control set to 10
watts. The power control changes the output power. The
internal RF output meter now displays output power
correctly.

I am now proceeding to complete the Part III test.

Best,

Joe Szczubelek - K9DMV    

 

--- Don Wilhelm <[hidden email]> wrote:

> Joe,
>
> The initial problem to be solved is that there is no
> indication of power
> output being fed back to the K2 microprocessor.
>
> The most likely source is a bad solder connection
> and the second most likely
> is a misplaced component.
>
> Keep your testing periods short, ignore the high
> current messages for now,
> and proceed as follows:
> Start your search at RF Board diode D9 - if all is
> well at that point, there
> will be a DC voltage during transmit periods - how
> large it is depends on
> the amount of RF output, for now just be certain you
> have a good solid DC
> voltage there - anything over a volt or so will
> indicate that the RF Output
> Detector is working.
>
> Next point is on the Control Board - the VFRDET
> signal which appears at pin
> 10 of P4 - the DC voltage during transmit should be
> about the same as you
> measured at the cathode of D9.
>
> Lastly, check the VRFDET signal at the
> microprocessor - U6 pin 2.  The
> voltage should be about the same as at P4 pin 10 if
> R12 is properly in
> place.
>
> Let us know where the VRFDET signal path is broken.
>
> 73,
> Don W3FPR
>
> > -----Original Message-----
> >
> > The build for K2 ser # 5628 has been going well
> until
> > I got to the "Alignment and Test Part III"  40
> meter
> > transmitter alignment section.
> >
> > Problem:
> >
> > With current set to 2.0 AMPS and the power control
> > fully CCW I measured 7 watts on an external
> wattmeter.
> > The internal wattmeter had NO indication. When I
> press
> > the "tune" control with the display set for
> voltage
> > and current I see 13.3 volts and 1.88 amps. The
> > current will start to slowly rise at .02 amps per
> > second and will reach 2.00 amps in about 10
> seconds
> > and the "HI CURRENT" message will appear with 7
> watts
> > output.
> >
> >
> --
> No virus found in this outgoing message.
> Checked by AVG Free Edition.
> Version: 7.5.430 / Virus Database: 268.15.6/567 -
> Release Date: 12/4/2006
> 7:18 AM
>
>

 
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