Phil, The problem will be found in the VFO Range Selection area. Look at the schematic for the RF Board sheet 1. Check the soldering of C71 and C72 and relay K13. It is possible that when hot, the contacts of K13 (and possibly K14) are not making good contact. Set to 80 meters and wait until the failure occurs, then power the K2 off and quickly (before things cool), check for continuity between K13 pins 3 and 4 also between pins 7 and 8 - both should be zero ohms - if not, the relay has failed. Check K14 in a similar manner, but set to 40 meters - after the failure, you should have continuity between pins 3 and 4 of K14 and also between pins 7 and 8.
The relay pins are numbered like an IC (pins 1 and 10 are at the same end). Look for the round solder pad at pin 1 (or the end with the white stripe). This is either a temperature related solder connection or a relay contact problem. 73, Don W3FPR Phil-W6TQG wrote: > Hi Don, > > Thank you for your help. Yes, it appears to be the VFO. The VCO readings > at TP1 for 20, 30, 40 and 80m are normal when the K2 is cool, but when > hot the readings are near 15,600 for 40 and 17,257 for 80. No wonder I > can't transmit or receive! 20 and 30m appear to be normal when hot. > > What do you suggest I look at next? > > 73, > Phil > > > >> -----Original Message----- >> From: Don Wilhelm [mailto:w3...@embarqmail.com] >> Sent: Tuesday, June 01, 2010 6:08 AM >> To: Phil-W6TQG >> Cc: elecraft@mailman.qth.net >> Subject: Re: [Elecraft] K2/100 Has No Output on 80 or 40 When Hot >> >> Phil, >> >> To use the base K2 BNC antenna jack, you must remove the >> KPA100 - if you >> attempt to use that jack, the load impedance between the base >> K2 and the >> KPA100 will not be correct, and "strange happenings" will be present. >> >> A total lack of power (yes, a display of 0.1 or 0.2 watts is >> actually no >> power out) is most likely a problem either in the bandpass >> filter or a >> problem with the VFO. Try the VFO first - set the frequency >> to the low >> end of the band and check the frequency with the counter probe in TP1 >> using CAL FCTR - compare your frequency reading with the chart on the >> Schematic Key page. If you want to calculate the proper VFO >> frequency >> it should be within a few kHz of the frequency on the dial >> plus 4915 for >> bands below 15 meters. >> >> Check all the components in the bandpass filter area for 40m >> and for 80 >> meters. On 40 meters, be certain C6 is properly installed >> between the >> two outer holes of the J15 position (the center hole should be empty). >> >> 73, >> Don W3FPR >> >> Phil-W6TQG wrote: >> >>> Every since the last Field Day, my K2/100 (#3713) loses >>> >> output, and the >> >>> receiver goes dead, on 40m and 80m when it gets hot. This occurs for >>> power levels of 9 watts and 100 watts. The 30m through 10m >>> >> bands are OK. >> >>> I can easily replicate the problem when the power amp is >>> >> connected, but >> >>> so far it seems to be OK when it is completely unplugged >>> >> from the K2. >> >>> Turning off the power amplifier through the Secondary Menu >>> >> does not make >> >>> a difference. While transmitting at 9W, the readings on the >>> >> display for >> >>> 40 and 80 are "0.1 1.01 - 1". With the power amplifier >>> >> connected to the >> >>> K2, I temporarily connected the antenna to J4 on the K2, so >>> >> that I could >> >>> bypass the power amplifier path. This did not help the dead >>> >> reception on >> >>> 40 or 80. I also tried connecting a dummy load through a >>> >> power meter to >> >>> J4 and transmitting at 9W. Again 40 and 80 didn't work but >>> >> the higher >> >>> bands were OK. >>> >>> I am assuming that the problem is in the LPF of the power >>> >> amplifier, but >> >>> am not sure 30m is OK, while 40 and 80 are not. Any hints would be >>> appreciated. >>> >>> 73, >>> Phil W6TQG >>> >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:Elecraft@mailman.qth.net >>> >>> 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
