On Sep 1, 2012, at 9:02 PM, Don Wilhelm <w3...@embarqmail.com> wrote:
> As for your wattmeter problems, I suspect that the diodes D16 and D17 may be > "half bad". Yes, that is rare, but possible - they have been damaged enough > to change their characteristics but not make them either open or shorted. > > I would recommend arbitrarily replacing them and then try the wattmeter > calibration again. > For initial settings, adjust R26 to produce 43k ohms to ground as measured at > U5 pin 5, and R27 to give 43k ohms as measured at U5 pin 3. > > After that do the null adjustment and see what happens. Don, Just wanted to report a resolution of my KPA100 problems. I noted earlier that replacing the shorted U6 - EL5146C brought the KPA100 back to life, but the rig was giving me some odd wattmeter and SWR results, especially on 80 and 160m. Replaced D16 and D17 with the proper 1N5711 diodes did the trick. I managed to test one of the diodes I removed (the other was destroyed in the desoldering process), and it showed a nearly correct forward voltage on my DVM, and about 3 times that value when connected in reverse. The diode action of the part was clearly compromised. A new part gave a low forward voltage, and an open when connected in reverse. I suspect these diodes, and possibly the EL5146C might have been damaged by a stray static discharge sometime in the last year. I ordered 10 of these diodes from Mouser. They are only $0.10 apiece, so it makes sense to stock spares. With the new diodes in place, the SWR Null Adjustment went well, giving a clear null down below 100 mV. More importantly, it read an SWR of 1.0 on all bands. The rest of the alignment went smoothly, and the rig appears to be producing the correct power levels on all bands. Made a quick contact with HA8RM on 80m just before writing this message. Thanks for your help! ______________________________________________________________ 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
