high current with KXB3080

[Frederick Dwight]

Bruce,
    When I built and installed my KXB3080 modification I had high current on 80 meters...over 900 ma with a 12 volt supply.  However in my case I had high power on
80 meters...5 watts and around 4 watts on the other bands.  To troubleshoot this problem, I operated the kx1 out of the case for short transmit periods with about an 8 volt supply.  I had used a piece of insulation on the 2 close wires on the LPF board and verified that this was not my problem.  However whenever I pried the LPF board slightly away from the main board (1mm??) the 80 meter current dropped to a normal value and power on all bands was OK.  I never identified the problem, but apparently something was shorting with the LPF board snug against the main board.  With the LPF board pried slightly away there is no problem.  I do not think it is a cold solder joint since I can now tap the boards, wires, torroids, etc and nothing bad happens.  Perhaps when installing the LPF board against the main board a piece of tape or other insulation between the boards would prevent a short.  I now get between 3.0 watts and 4.1 watts on the 4 bands with my 13.7 volt supply (current about 600 ma)  and about 1.5 watts with an 8.2 volt supply.
  I also did the L3 modification and the power resistor modifications.  Possibly something is shorting on your LPF board.....or even the L3 modification.  For sure I would not test with full voltage, but with a fused power supply with something like 7 or 8 volts until you find the trouble.  
  PS...I had fun with my 5 watts on 80 meters for a few days until my conservative nature kicked in and I fixed the "problem".  No spectrum analyzer here, so who knows  what frequencie(s) my 5 watts was on !!!
                        Rick   KL7CW   Palmer Alaska   KX1 #  798
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[Ron D'Eau Claire-2]

Rick, KL7CW, wrote

"... whenever I pried the LPF board slightly away from the main board
(1mm??) the 80 meter current dropped to a normal value and power on all
bands was OK.  I never identified the problem, but apparently something was
shorting with the LPF board snug against the main board.  With the LPF board
pried slightly away there is no problem.  I do not think it is a cold solder
joint since I can now tap the boards, wires, torroids, etc and nothing bad
happens.  Perhaps when installing the LPF board against the main board a
piece of tape or other insulation between the boards would prevent a
short..."

-----------------------------------

There should be nothing to short to on the KX1 main board under the LPF1
board. There's only one solder pad under the LPF1 board. That is for the
inductor common lead from the LPF. (Originally it was one of the inductor
lead pads.) I wonder if you were shorting the inductor common lead to
something on the LPF1 board? It's a bare wire that has to bend over a bit to
reach the solder pad. Could it be pushed up against one of the solder pads
on the LPF1 and causing a short until you pull the LPF1 away from the KX1
slightly, which will straighten and move the inductor common lead slightly?

Ron AC7AC

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