Bob - Having had to ship my 10 month old KPA500 back to Elecraft twice in its short life, I was fearing the worst when I started reading your post.
What a relief to hear the actual cause ... and I can well imagine it was doubly so for you! 73 Lyn, W0LEN -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Bob Witmer Sent: Sunday, May 17, 2020 11:31 PM To: Elecraft@mailman.qth.net Subject: [Elecraft] An Unusual KPA-500 Failure - That Wasn’t ... I thought the group might find a recent KPA-500 troubleshooting experience interesting - and possibly be of help with future troubleshooting efforts. For reference, my station consists of a TS-890 followed by a KPA-500 and a KAT-500, that interfaces different wire antennas depending on the operating band. One Friday night after dinner, I headed to the ham shack to check out 160M. Since it had been raining I needed to check the antenna SWR. After completing a KAT-500 (KAT) tuning cycle at low power, I had a new tuning solution and switched in the KPA-500 (KPA) for confirmation. I started at low power and slowly increased the power level. At around 100 watts output from the KPA I was rewarded with what I call the “Allen-Bradley” smell, a slight cloud of smoke and a KPA low voltage alarm! I immediately cut power and tried to reset the KPA alarm but couldn’t by cycling the power off/on. So I unplugged the KPA from the AC power. After reconnecting the power and turning the KPA on, the alarm was gone. I repeated the tuning process, with almost the same results except the smell and smoke were more noticeable. At this point I took the KPA completely off line, disconnecting all control and RF connections, and raised the power out level of the TS-890 to 90 watts, which then confirmed normal operation via the KAT. At this point I began to think about returning the KPA for repair and wondered how long it would take to get it back, considering COVID-19 issues. For some reason I decided to try the KPA500 - KAT500 pair one more time. This time I moved closer to the KPA500 to try to get a clearer idea of where the “smoke” was coming from. I slowly raised the power one more time and the KPA shut down just like before, but this time I noticed the “smoke” was coming from what looked like the rear of the amp. I moved the KPA and noticed the smell was still very strong - and at the rear of the KPA. It was then I noticed that the AC line surge suppressor the KPA was plugged into, in a wall socket directly below the back of the operating table with the KPA, was the source of both the smell and “smoke”. I bypassed the suppressor and was relieved when the KPA returned to normal operation. Somehow, when the current draw through the suppressor reached a certain level, failing internal suppressor component(s) overheated and presented a line voltage drop to the KPA500 sufficient to trigger the internal low operating voltage alarm. With the suppressor located directly behind and below the KPA, it seemed like the smell and smoke were coming from the KPA - and the KPA was failing since the KPA low voltage alarm activated. So of course, always check to make sure the equipment you’re troubleshooting is actually “plugged-in” (following troubleshooting safety guidelines) - but also check to make sure any in-line power surge suppressors are working correctly. 73, Bob, W3RW ______________________________________________________________ ______________________________________________________________ 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
