Don and Group, Thanks very much for the responses. I will look at the schematic and determine the associated resistors with D9 and replace it. I will also order KPA100 D16 and D17 diodes from Elecraft. Ariel NY4G
> Date: Fri, 26 Oct 2012 08:10:37 -0400 > From: [email protected] > To: [email protected] > CC: [email protected] > Subject: Re: [Elecraft] K2: High SWR On Dummy Load > > Ariel, > > You may indeed have a problem with D9 and the 3 associated resistors in > the base K2, BUT when the KAT2 or the KPA100 is installed, that circuit > is ignored. > Both the KAT2 and the KPA100 contain a true wattmeter that is positioned > right at the output and used for power control. > > The K2 microprocessor reads the actual output and compares that to the > power knob setting. That result tells the microprocessor how to adjust > the drive. Unlike other ham transceivers, the K2 uses a closed loop to > control the power instead of simply adjusting the drive. > > What that also means is that the wattmeter in the KPA100 is not working > (you have shown that the one in the KAT2 is working OK). As I indicated > before (and also indicated by your high SWR indication) there is a high > probability that KPA100 diodes D16 and D17 have been damaged. > > When the diodes are damaged, the output back to the MCU is most likely > zero, and the MCU *thinks* there is no power output - it then increases > the drive to the maximum in an attempt to develop power. The result is a > HiCur warning and stress on the base K2 PA transistors. > > Replace KPA100 D16 and D17 as the first order of business and after that > you can investigate any remaining problems. Note that those diodes can > be "half bad" and may show as good with a diode test - replacement is > the first order of business. > > 73, > Don W3FPR > > On 10/25/2012 11:31 PM, Ariel Jacala wrote: > > Don > > > > The K2 with the ATU behaves as expected - internal meter agrees well with > > the external meter, current draw is as expected, and so forth for various > > power levels up to 10watts checked out. It was connected to a dummy load. > > > > Without the ATU and the dummy load connected to the base K2 antenna, things > > are rather strange.... At 2 watts set on the power knob, output on the > > external meter is 2.7 watts and current draw is 0.96 amps; at a knob > > setting of 2.4 watts, output is up to 7 watts on the external meter and > > current draw is 1.4 amps; at a knob setting of 2.5 watts, power output is > > 10 watts and current draw is 1.96 amps; at 3 watts knob setting, I get the > > high current warning, and the external meter is pegged. > > > > This leads me to believe that the base K2 is overdriving the KPA100. At low > > power settings - 5 watts, I was pegging the LEDs indicating power on the > > LDG100 autotuner, at over 125 watts. > > > > Ariel NY4G > > > > Sent from my iPad > > > > On Oct 25, 2012, at 11:51 AM, "Don Wilhelm" <[email protected]> wrote: > > > >> Ariel, > >> > >> Do not be too quick to conclude that there is something wrong with the > >> base K2. The basic K2 uses only an RF voltage diode to display the power > >> output, and it may not be exact - it depends on the load and may vary from > >> band to band - if it only off by a watt or two, then all is OK That is > >> bypassed when the KAT2 or KPA100 is installed. > >> > >> Yes, do check with the external wattmeter - both with and without the > >> KPA100. I still think KPA100 diodes D16 and D17 are highest on the suspect > >> list with other KPA100 wattmeter components being second on that list. > >> > >> 73, > >> Don W3FPR > >> > >> On 10/25/2012 11:18 AM, Ariel Jacala wrote: > >>> Thanks to Jim, Vic and Don for the return comments > >>> > >>> I disconnected the KPA100 and put on the K2 top with the KAT2 ATU. With > >>> the K2 ATU connected and the dummy load connected - the SWR correctly > >>> reads 1:1 with menu set for CALS. With the menu set to CALP, the power > >>> levels appeared to modulate correctly with the PWR knob although this is > >>> an item i have to double check. With the ATU disconnected, the displayed > >>> power on tune differs from the power setting. This suggests to me that > >>> there is something wrong with the base K2. I still have to do what Don > >>> suggested about connection to an external watt meter. > >>> > > ______________________________________________________________ > > 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 > > > ______________________________________________________________ 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
