Don, I found the problem: the short wire that connects the ungrounded side of C1 to the SO259 jack had a poor solder connection.
I figured that since C1 wouldn't tune, there had to be a problem in that bridge circuit prior to U5. I started tracing each component's connections with my Ohmmeter, and I finally discovered that the ungrounded solder pad for C1 didn't connect. Thanks for your help, Don. You're a terrific resource and your extraordinary efforts and patience in helping bewildered folks like me are really appreciated. 73 Dick, K0KK On Tue, Oct 3, 2017 at 3:10 PM, Don Wilhelm <donw...@embarqmail.com> wrote: > Dick, > > That is mystifying. With the diode "backwards", you get a positive > voltage at U5 pin 3 - that should be the correct orientation for D17. > > For the power indication, check the polarity of the voltage at U5 pin 5 - > if that is negative, then D16 is also backwards. > > You may have a situation where T4 is not wound with the correct sense, > although the orientation of the diodes should still produce a positive > voltage at U5. > Something is strange here. > > 73, > Don W3FPR > > On 10/3/2017 3:44 PM, Dick Lamb wrote: > >> Yes, the voltage is negative on U5 Pin 3, but D17 is not installed >> backward--i.e., the cathode band is on the side away from the coax >> connector, as shown in the manual. I tried reversing the diodes (cathode >> band on the side of the the coax connector), and Pin 3 voltage does drop to >> millivolt positive range, and the SWR shows 1:1, but the power output >> doesn't change regardless of the "power" knob setting. I verified that the >> diodes are banded correctly with a semiconductor tester. Dick, K0KK >> >> On Tue, Oct 3, 2017 at 1:20 PM, Don Wilhelm <donw...@embarqmail.com >> <mailto:donw...@embarqmail.com>> wrote: >> >> Dick, >> >> Is that voltage at U5 pin 3 actually negative? If so diode D17 is >> backwards - the voltage should be positive in all cases. Yes, C1 >> will not adjust if the D17 polatity is wrong. >> You can refer to the parts placement diagram at the back of the >> KPA100 manual if you cannot see the silkscreen clearly. >> >> After putting D17 in correctly, recheck the 43k initial setting of >> R27 and go from there. >> >> > ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
