K3 – KPA3 ERR
12V – FAULT FOUND
Hi all, while
experimenting on the K3 (SN 01757) 1st mixer replacement, with the
I7SWX 2T H-Mode Mixer , we proceed on the calibration routine on TX. No errors
were reported for the 5W and 50W power output.
While testing
the RF output (dummy load) on all band we discovered the 80m band would not output more than
65W, while on all other bands we were around 100+ W. The K3 was never tested or used on 160 and 80m by the owner.
We believe we
have a problem with the low pass filter.
We checked for burning or damage the
LPF area. To do this the KP100 was removed and then reinserted. Testing the K3
we had KPA3 ERR 12V. We could not understand why we had such a failure as
nothing was done to the amplifier and main unit.
Checked ckt
breaker and 12V PA voltage, all OK. We searched on the Elecraft List for KPA3
ERR 12V thread but we could not get any valued information, apart info on
potential problems due to contact pins oxidation. We replaced connectors with
golden pins ones but no changes.
From Elecraft support we got some suggestions
regarding what to check or send the equipment to a service center. As
homebrewers this last point is not easy to be accepted … hi.
Manual does not
explain how this Error is being monitored. We studied the circuit starting from the
KPA3. 12PA is being detected by R16 and R15 on the KPA3 and generate signal
V12SPA on pins 11-12 on P68A. The V12SPA signal is then processed by the CPLD.
The V12SPA voltage is around 3V for old K3 and 0.6V with new ones or
those where the 1N4148 diode has been added (KPA3 12V Sense Mod, Rev B).
What we
discover is that we had no voltage at V12SPA.
Checking the KPA3 board we found out
one of the metal contacts of R16 vas broken. Maybe the removal and reinsertion
bent the PCB and the resistor was damaged or it was critically at assembly. Now
K3 is operating OK but we still have the low power problem on 80m. We have
requested to Support the components data as values are not reported on the
circuit diagram. Anyone had similar problem?
Best 73
Gian,
I7SWX; Sergio, IK8TNG; Mario, IZ8DBJ
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