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, probably a wrong component(s). 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. Elecraft support suggested some controls to be done, like we did, or send it to a service center. 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. We still have the low RF output power problem on 80m. We have requested to Support the components data as values are not reported on the circuit diagram. Anybody had a similar problem? Best 73 Gian, I7SWX; Sergio, IK8TNG; Mario, IZ8DBJ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
