KX-3 ERR TXG on 50MHz

[Drew Arnett]

Hi,

This radio has been problem free.  (And a heck of a lot of fun!!!)

I've never recalibrated anything, as per the manual, there has been no
need.  I have done FW upgrade at least once and that is currently
02.38/01.37.

Just started getting "ERR TXG" on 50 MHz.  Have seen several values in
the D=xxx message as well.

Manual has:
-----
Error msg:  ERR TX

Problem:  Transmit gain constant out of range

Troubleshooting steps:  If this only occurs on one or two bands, there
could be a problem with a band-pass or low-pass filter. Also try
re-doing Transmit Gain calibration (pg. 33).
-----

Did some bench testing with a dummy load.  I checked and problem only
occurs on 50 MHz.

Suspect degradation.  Would be nice to resolve before the June VHF!  :-)

Did not try redoing the transmit gain calibration, as the
troubleshooting steps suggests otherwise.

With tech support, got as far as the suggestion of reducing power
supply sag.  Did have some IR drop, especially on 50 MHz, so swapped
for lower IR drop power supply cable.  Confirmed bench supply itself
isn't sagging.

So, what I measure now:

At 28 MHz RX mode measures 13.60 V on DMM (on outside of DC coaxial
power plug), 13.8 V on KX3 meter, and 0.17 A on KX3 meter.

At 28 MHz TX constant 4 W carrier measures 13.55 V on DMM (on outside
of DC coaxial power plug), 13.4 V on KX3 meter, 2.18 A on KX3 meter
and 1.2 to 1 VSWR on KX3 meter.

At 50 MHz RX mode measures 13.60 V on DMM,  13.8 V on KX3,  0.19 A on KX3.

At 50 MHz TX constant 4 W carrier measures 13.53 V on DMM, 13.3 V on
KX3, 2.9 A on KX3 and 1.6 to 1 VSWR on KX3 meter.

VSWR is better of course below 28 MHz.  (Microwave dummy load.)

Of course, I don't have baseline measurements from when I first
received the radio to compare against.  If anyone can make similar
measurements of their KX3 for comparison, that would be very
interesting.  Want to know about TX current draw and the 1.6 to 1
VSWR.

Manual specs "1 to 2 A typical in transmit".  Current is on the high
side of that at 28 MHz even with the power backoff.  3A on 50 MHz,
though?  And, yes, the PA temp climbs quite quickly.

Needs to go in for repair?  No problem with that if that's the thing
to do.  (Schedule is probably too tight for June VHF, and I'm sure the
stay at home order doesn't help.)  I can do some trouble shooting and
component swap here, no problem.  My biggest limitations are time
(work seems even busier with stay at home) and lack of a body of
knowledge regarding this specific radio.  I haven't popped it open for
visual inspection, yet.  Probably should do that especially around the
6m filters and the active and electromechanical RF switches.

If I don't have a backup rig, I'm either not a serious contester, or
i'm wating for a K4.  Not sure.  :-)  Again, this radio has been a ton
of fun!  A little sad to run into my first problem with it, but it's a
field radio, and I don't expect miracles.

Thanks in advance,

Drew
n7da
San Diego
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