[Elecraft] [K2] PA ALC problem on CW

[picmaster at mail.bg]

Hi everyone,

I have an issue with my K2 internal power amplifier. After completing the
kit assembly I went on to pass through the transmit test procedures with
a good dummy load, but I got the famous "HiCur" over-current warning
message when using the TUNE button (any band, any "POWER" setting).

Initially I thought that I had a short somewhere, but in the end I found
out that the transceiver was consuming 4-5A because it was really producing
some power on the dummy load (about 20W distorted signal!).

So the PA looks fine this time and I started to wonder how actually the radio
was controlling the output power (when I touch the front panel "POWER"
control, the display reacts properly and the power is changed in the range of
0.1-15.2W, but this doesn't change the PA output - it still puts 20W when
pressing TUNE).

// Small offtopic - the POWER know has some dead region in the most left
// position, maybe because the diode analog inputs multiplexing...

I can confirm that the "RF Output Detector" circuit (RF board) works and the
signal from this circuit reaches pin 2 of U6 (Control Board). Unfortunately I
can also confirm that the 8-bit DAC (MAX534) doesn't output any voltage
on "OUTA" when pressing TUNE. The DAC output is not shorted to ground,
so my estimation is that channel "A" is defective.

I was wondering actually whether I can disconnect pin 2 of U8 (MAX534)
and try to apply external regulated 0-5V control voltage directly to the BFO
attenuator ("V ALC" signal, RF Board), in order to observe whether this will
change the transceiver output power when TUNE.

My question to you guys is: can you share what's the actual voltage of
the "V ALC" signal in your radios for power values 1W, 5W and 10W on CW?

Thanks in advance for your help,

Nikolay (LZ1NRD)

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