David, Actually using a switch in the antenna line to switch in the dummy load is best. If you consider that with a PL-259, the center conductor is connected before the shell, so if there is a charge on the antenna due to wind, rain or lightning static, it can zap the diodes.
You can get the diodes most anywhere. I usually get mine from Diz - www.partsandkits.com, inexpensive and he ships quickly. Thank you for your kind words. 73, Don On 6/11/2011 7:48 PM, david wrote: > Don, > > Thanks for confirming my diagnosis. I *usually* remember to disconnect > the antenna when I am not operating. > > I assume that the standard 1N5711 will work, Elecraft doesn't screen > them for any special characteristics do they? > > As always, I'm sure I not the only one that appreciates the knowledge > you bring to the Elecraft community. > > David AJ4TF > > > On Sat, 2011-06-11 at 18:13 -0400, Don Wilhelm wrote: >> David, >> >> Yes, it looks like U5, U6, Q10, Q11 and the associated components are >> behaving as they should. >> >> It certainly could be that D16 and D17 are not either open or shorted, >> but are not fully functioning as they should. The fact that you could >> only get the resistance measured at the wiper of R26 as high as 30k does >> confirm that -- replace the diodes. >> >> It also seems from your description that things are a bit intermittent >> and erratic, so while you are in there to replace the diodes, give the >> soldering in the wattmeter area (particularly T4) a good inspection and >> perhaps re-flow the solder with a hot iron (800 degF for the KPA100 >> board), and perhaps add a tiny bit of new solder (actually you are >> adding a bit of flux). >> >> Yes, those diodes are sensitive to lightning surges. Switch the K2 >> antenna to a dummy load when not in use for best results. >> >> 73, >> Don W3FPR >> >> On 6/11/2011 4:42 PM, david wrote: >>> K2/100 s/n 7006 >>> Initial symptom: No control of output power at any knob setting. At >>> 1-9W setting, output was>10W as measured by external wattmeter, SWR >>> read back>9.9 (external meter shows around 1:1). At 10-100W setting, >>> output>100W, SWR>9.9. HI REFL message displayed. >>> >>> Unit was previously working fine for several months. >>> >>> Troubleshooting procedure I used: >>> >>> 1) Disassembled KPA100 from radio (but still connected). >>> Repeated test using 50 ohm dummy load, same results. >>> SWR reading>9.9 >>> >>> 2) Set to 40M, 7200 kHz, set power to 5W, and made the following KPA100 >>> measurements during TUNE cycle: >>> U5-5: 0.2V (VFWD) >>> U5-7: 0.2V >>> U5-3: 2.01V (VREF) >>> U5-1: 2.01V >>> >>> So, I assume the microcontroller is seeing this and measuring a high >>> SWR. HI REFL message was displayed. >>> >>> 3) Using diode check function on Fluke 8021B, measured D16 and D17 in >>> circuit, each showed approx. 0.4 V forward bias, and open reversed. >>> However I am not yet convinced that the diodes are not damaged in some >>> way (see below). >>> >>> 4) I went through the SWR Bridge Null adjustment procedure in the KPA100 >>> manual. However, I was unable to get a measurement of 43 kohms on the >>> wiper on R26 to ground, I was only able to get a maximum of 30 kohms, >>> and with the wiper centered, it read about 23 k ohms. I left both R26 >>> and R27 centered. >>> >>> 5) At 5W power, I was able to adjust C1 to obtain a 1.0 SWR reading, >>> noting that C1 appeared to be in almost the same position as before. >>> >>> 6) Set to 40M, 7200 kHz, set power to 5W, and made the following KPA100 >>> measurements during TUNE cycle. Indicated power 6.0W, indicated 1.0 >>> SWR reading from display. In each case, I allowed about 5 seconds for >>> the output to stabilize before taking each measurement. >>> U5-5: 1.4V >>> U5-7: 1.4V >>> U5-3: 0.02V >>> U5-1: 0.02V >>> U6-6: 2.8V >>> U6-3: 1.4V >>> At this point I am reasonably certain that U5 and U6 are working. >>> >>> 7) set power to 15W, (heard relay switch to KPA100) and made the >>> following KPA100 measurements during TUNE cycle. Indicated power 15W, >>> indicated 1.2 SWR reading from display, external wattmeter showed>20W >>> and 1:1 SWR. >>> U5-5: 2.25V >>> U5-7: 2.25V >>> U5-3: 0.3V >>> U5-1: 0.3V >>> U6-6: 1.41V >>> U6-3: 0.71V >>> >>> 8) set power to 20W, and made the following KPA100 measurements during >>> TUNE cycle. Indicated power 20W, indicated 1.6 SWR reading from >>> display, external wattmeter showed ~40W and 1:1 SWR. >>> U5-7: 2.55V >>> U5-3: 0.6V >>> U5-1: 0.6V >>> U6-6: 1.62V >>> U6-3: 0.81Vmeter showed>40W and 1:1 SWR. >>> U5-5: 2.55V >>> U5-7: 2.55V >>> U5-3: 0.6V >>> U5-1: 0.6V >>> U6-6: 1.62V >>> U6-3: 0.81V >>> >>> 9) set power to 40W, at this point, I was able to re-adjust R26/R27 to >>> match the externally measured output power to the indicated power >>> (within a few watts, and limited by the accuracy of the external power >>> meter). >>> After adjusting R26/R27: Indicated power 42W, indicated 1.8 SWR >>> reading from display, external wattmeter showed ~40W and 1:1 SWR. >>> U5-5: 3.76V >>> U5-7: 3.76V >>> U5-3: 1.15V >>> U5-1: 1.15V >>> U6-6: 2.37V >>> U6-3: 1.18V >>> >>> 10) set power to 60W, Indicated power 60W, indicated 2.3 SWR reading >>> from display, external wattmeter showed ~60W and 1:1 SWR. >>> U5-5: 4.4V >>> U5-7: 4.4V >>> U5-3: 1.72V >>> U5-1: 1.72V >>> U6-6: 2.78V >>> U6-3: 1.39V >>> >>> So, after all of this, my conclusion is that D16 and D17 may be leaky, >>> or somehow defective, and providing invalid voltages to the measuring >>> circuit. I do not believe that U5 or U6 are defective, and it appears >>> that the microcontroller is controlling the power based on the voltages >>> it is seeing. >>> >>> I would appreciate any other opinions or insight, or any other >>> suggestions on what else to check. In the meantime I'll go ahead and >>> order some replacement 1N5711's. Static electricity? Lightning? >>> >>> David AJ4TF >>> >>> >>> ______________________________________________________________ >>> 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 > ______________________________________________________________ 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
