Hi all!
Another K3 has been built! K3 #1851 was ordered on 17 June, shipped
on 30 September and was delivered and subsequently built today, 3
October. It's a K3/100, with KAT3, KBPF3, and KXV3. It has the stock
2,7 kHz, FM and 400 Hz filters. The KRX3 and accompanying filters are
on back-order (expected in about two months).
All calibrations and tests passed, but while trying the rig out on 40
meters, a nasty problem turned up. Transmissing at full power let
some of the smoke out. I understand the desired operating practice is
to keep the smoke inside at all times. After removing the top cover
and doing some more tests at reduced power (30 to 50W), I found out
that one toroid on the KAT3 board is getting very hot. It is the blue
toroid, possibly labeled K16 (can't quite see) which has 3 windings
on it. I'm guessing this toroid is part of the circuit sensing the
reflected power.
The problem occurs only when transmitting on 40 meters into my
antenna (a 2x24 meters doublet), using the KAT3 in AUTO mode. The
MFJ-949E external ATU sits in-line, connected with about two feet of
coax, but is switched to bypass mode. Interestingly, the MFJ does
show a very high SWR (1:6 or worse), while the K3 shows a perfect 1:1 match!
The problem with the heating occurs only on 40 meters; on other bands
it stays cool. Still, on these other bands, the external tuner shows
high readings too. When transmitting into the MFJs dummy load, both
the K3 and the MFJ agree that the SWR is perfect.
Does anyone know what could cause this? FWIW, I am still using the
factory-supplied firmware (MCU 2.38 and DSP 1.90).
Thanks in advance,
Frank PA4N
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