Steve,
If "hooked up backwards" means that the DC power was connected with
reverse polarity, that will normally cause no harm to the K2 because
there is a series reverse voltage protection diode in the input power
line. The burned trace on the mic jack pin 5 suggests that something
different happened to it.
Try replacing D9 with a 1N5711 diode and see what happens. The power
output into a good dummy load will normally be within 0.2 watts of the
set power if all is working right. You older K2 has a 1N34 diode at D9
and it is not as accurate over the full frequency range as the 1N5711.
If you have not done so already, record the menu settings, especially
the filter settings and do a Master Reset (hold the 4, 5, and 6 buttons
in while powering the K2 on). Then run CAL PLL and restore the menu
settings. The fact that the problem goes away if you swap control
boards suggests that there may be some problem with the EEPROM contents,
and a Master Reset should 'clean it out'.
Set CAL CUR to 3.50 instead of 2.50 and see if the HiCur messages go
away. If they continue, you may have to replace the PA transistors.
Another thing to check is the DC voltage at the base of Q7 and Q8 during
a TUNE - it should be in the range of 0.60 to 0.64 volts. If not,
replace Q11 and Q13.
73,
Don W3FPR
On 10/5/2014 1:36 AM, KY7K wrote:
I forgot to mention that all testing is into a known good DL1 dummy load that
I’m also using for my external power readings.
Any wise insights are most welcome!
Steve - KY7K
[email protected]
Get OUT and play radio!
On Oct 4, 2014, at 10:28 PM, KY7K <[email protected]> wrote:
I recently purchased a used K2 (Rev A) from a club that was not working because
it had been “hooked up backward”. That is the best anyone can remember as to
what happened to the radio ~7 years ago…
Currently, the power output as displayed on the radio and on an external power
meter is very unstable and does not match the power setting desired. This is
not just a little off, I can select 1W on the radio and then hit the tune
button 5 times and might get .4W, 6.7W, HI-CUR, 9.0W, 1.2W.
This is the QRP K2 with SSB, NB, KIO2 and DSP options. The problem occurs with
or without the option boards installed.
Background:
When I first tested it, it would power on but the only function that was
operational was the power control. Every other knob and button was
non-functioning as if the cpu was hung up. The radio was not transmitting in
this state.
I had a old CPU (U6) from my other K2 that I installed as a test and that
seemed to fix the problem, at least in receive. I, unfortunately, did not test
it in transmit.
I ordered a FWK2MCIO kit to get a new cpu and also ordered all the mod kits for
the Rev A to Rev B upgrade, once they came in I installed everything and while
performing the the calibrations after the upgrade discovered that the transmit
power was very unstable between transmissions.
Other than the bad U6, the only other issue I found was that the PCB trace from
pin 5 of the Mic connector on the front panel board was basically missing, from
getting shorted to +12V I assume, it disintegrated when touched...
I’ve narrowed the issue down to the control board, since if I swap the control
board from my working K2 into the bad radio the power issue disappears.
I’ve checked VRFDET, VALC, and VPWR on the control board and they are all OK
best I can tell, and I’m now at a loss where to look next.
Note: the power level is stable once it settles on some random output power.
The power level is random from one transmission to the next.
The following links are images showing a tune cycle.
The first image shows the full scan with the radio set to ~1W and actually
putting out ~.4W. The second image is zoomed in on the start of the cycle.
https://www.dropbox.com/s/i64sw2ue2405roe/k2_0_5w_full.png?dl=0
https://www.dropbox.com/s/qe297am756igbd4/k2_0_5w_zoom.png?dl=0
This is with the power set to ~7W and the radio indicating hi-cur, before
settling down to ~6.4W
https://www.dropbox.com/s/tqxzi3yk13gye4g/k2_hicur_full.png?dl=0
https://www.dropbox.com/s/6qz10478zt66tjd/k2_hicur_zoom.png?dl=0
Steve - KY7K
[email protected]
Get OUT and play radio!
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