Transmit power control problem

[Pauli Nunez EA3BLQ]

Hello friends and greetings from Barcelona, Catalonia, Spain,

That's me again looking for help from you, the Elecrafter's community.

After having solved my recent "Info 80" trouble and since I had upgraded my
KPA100 and all the F/W, my K2's configuration got quite disarranged, I
decided to implement all the mods to upgrade my K2 rev A to a K2 rev B,
before getting into the configuring and aligning task (I had installed some
of the mods but not all) so I purchased the K2ATOBKT kit and did a lot of
disoldering and soldering. All has run as per the manual but (Why there's
always a but? Is it Murphy's Law?) now I have got a transmit power control
problem.

When I key down (TUNE) the K2 and independently of the value I set in the
POWER Control (be it 0.50, 2.00, 5.00 or 10.00 watts) I always get the "Hi
Cur" message and the internal wattmeter drops to 0.3 watts, but the truth is
that the power transmitted into a very well calibrated 50 Ohm Dummy Load and
RF Power Meter (the QRP RF-Power Meter PM-1300a by SSB-Electronics) always,
and I mean always with independence of the K2 POWER Control, reads between
10-14 watts depending of the frequency.

Have made the resistance checkings and they are OK

My PS is a switched Daiwa SS-330 X with an output voltage of 13.8 v fixed
and an output current continuous of 30 A
Measuring the voltage at the K2 Aux 12v connector I get the following
readings:

K2 switched OFF = 13.84 v
K2 switched ON  = 13.62 v
K2 transmitting   = 13.16 v

With the Cal Cur set at 2.5 A, on my DMM I get the following current
readings:

K2 receiving   = 0.29 A
K2 transmitting = 2.51 A

The DC voltage readings for the PA finals Q7 and Q8 are:

Collector K2 receiving     = 13.60 v
Collector K2 transmitting = 11.98 v
Base      K2 transmitting =   0.62 v

DC voltage for the PA driver Q6

Collector K2 receiving     = 13.60 v
Collector K2 transmitting = 12.60 v
Base      K2 transmitting =   1.02 v
Emitter   K2 transmitting =   0.26 v

I fear the PA finals may be damaged so they do not obey the
POWER control settings, but am not convinced of that and
although I have the K2PAKIT ready, I do not want to replace them
unless it is necessary.

BTW, the heat sink is isolated from the Q7 and Q8 collectors.

Any ideas and/or suggestions will be much welcome.

Sure I am missing something but honestly, at this moment, I do not
know what. Look forward to hearing from you. Thanks in advance.

Best 73

Pauli, EA3BLQ
K2/100 # 1044
ea3blq(at)menta.net
ea3blq(at)qsl.net
URL: www.qsl.net/ea3blq





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[Don Wilhelm-2]

Pauli,

Let me restate your symptoms first so you can ignore my answer if no
match --
1). You have over 10 watts of actual power generated into your dummy load.
2). The K2 display shows only a small amount of power output
3). You are getting excessive current draw (HI CUR).

If ALL that is correct, the problem is in the VRFDET signal path somewhere.
The MPU is not sensing RF being generated and tries to increase the power.
Check the components in the RF Output Detector (schematic sheet 3 lower
right corner).  After that simple voltage divider and diode detector, the
signal finds its way to the control board and is present at pin 10 of the
AUX I/O header and then goes to pin 2 of U6 (there may be an 820 ohm
resistor in series before hitting the MPU pin, depends on your level of the
Control Board, the early ones did not have the resistor).

Also, if you did the keyclick mod, look carefully at that - it will
influence the ALC action, but will not likely produce the symptoms you
report.

73,
Don W3FPR

----- Original Message -----
>
> After having solved my recent "Info 80" trouble and since I had upgraded
my
> KPA100 and all the F/W, my K2's configuration got quite disarranged, I
> decided to implement all the mods to upgrade my K2 rev A to a K2 rev B,
> before getting into the configuring and aligning task (I had installed
some
> of the mods but not all) so I purchased the K2ATOBKT kit and did a lot of
> disoldering and soldering. All has run as per the manual but (Why there's
> always a but? Is it Murphy's Law?) now I have got a transmit power control
> problem.
>
> When I key down (TUNE) the K2 and independently of the value I set in the
> POWER Control (be it 0.50, 2.00, 5.00 or 10.00 watts) I always get the "Hi
> Cur" message and the internal wattmeter drops to 0.3 watts, but the truth
is
> that the power transmitted into a very well calibrated 50 Ohm Dummy Load
and
> RF Power Meter (the QRP RF-Power Meter PM-1300a by SSB-Electronics)
always,
> and I mean always with independence of the K2 POWER Control, reads between
> 10-14 watts depending of the frequency.
>
> Have made the resistance checkings and they are OK
>



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