Did you check D9 and other components on the RF board that provide the
VRFDET signal?
How did you check "VRFDET, VALC, and VPWR on the control board" if the
transmit power is unstable?
On 10/5/2014 08:28, KY7K 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!
--
73,
Vic, K2VCO/4X6GP
Rehovot, Israel
http://www.qsl.net/k2vco/
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