[Elecraft] K2 transmit low power, high current

[Don Wilhelm]

  Wayne,

The first place to look is the Low Pass Filters and possibly T4.
Make certain the number of turns on the toroids is correct - count the 
number of times the wire goes through the center of the core rather than 
counting turns on the outside.  When winding a toroid, a straight wire 
through the center of the core is one turn, a full wrap around the core 
is two turns.
Check and double check the windings of T4.  You should have two loops of 
white wire and 2 white ends (3 turns) on the side away from the PA 
transistors,
And on the PA transistor end you should see one green loop and 2 green 
ends of wire (2 turns).
The link wires should go straight through the hole on one side and then 
solder straight to the board - these do not loop through both holes.

Based on your readings, you may have a problem with the TX buffer (too 
much gain), but that is not what is causing the HiCur messages and low 
output.
After the HiCur messages are fixed, then double check the Buffer - check 
resistor values and soldering particularly R93 thru R96 and C150.

73,
Don W3FPR


On 4/28/2011 3:38 PM, Wayne Conrad wrote:
> K2 #7150 is assembled.  It receives, but shows low power and high
> current on transmit.  Doing the 40 meter transmitter alignment
> procedure, I get these results.
>
> When not transmitting: 13.6V, 0.22A
> TUNE, 5.0W selected: 5.0W indicated, 13.3V, 2.00A
> TUNE, 10.0W selected: "Hi cur" warning, 5.8W indicated, 13.2V, 2.50A
>
> During transmitter signal tracing, trouble first shows up in the
> "transmitter mixer, buffer, band-pass filter, T-R Switch" checks:
>
> (All measurements Vrms using RF probe, "key down")
> Xmit mixer output (U10, pin 4): Expected: 0.16, actual: 0.0019
> Buffer output (U9, pin 6): Expected: 0.200, actual: 0.0927
> Ratio of Buffer output to Xmit mixer output: Expected: 12:1  Actual: 49:1
> Band-Pass Filter Output (W6): Expected: 0.030, actual: 0.0318
> T-R Switch #1 Output (D1 anode): Expected: 0.029, actual: 0.0305
>
> The Pre-driver, Driver and PA voltages are, with one exception, also
> unexpected, but I'm guessing that's a result of the previous stage being
> all goofy:
>
> (All measurements Vrms using RF probe, "key down")
> Pre-driver output (Q5 collector): expected 0.120, actual 0.194
> Driver input (Q6 base): expected 0.026, actual 0.017
> Driver output (Q6 collector): expected 1.8, actual 2.8
> PA input (Q7 base): expected 0.38, actual 1.19
> RF detector input (D9 anode): expected: 2.0, actual 1.98
>
> Where should I look next?
>
> - Wayne Conrad
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>