Components fail for a reason, which almost always is because they have been over-stressed. Component manufacturers spend a lot of time analyzing their devices to determine their stress points, failure modes and safe usage areas. When we design equipment, we look at this information to make sure the component will perform exactly the way we need it to perform for the lifetime of the design, and that we do not stress the component so as to make sure that it remains in the safe zone. This is done for each and every component in the design. In some cases, such as high availability systems (think telephone switches and other mission-critical devices) the work is required by the customer in contracts, in others it is done to reduce the failure opportunities and thus the need for repairs. The arena of six-sigma design was created to directly address component design and reduce opportunities for failure.
When approaching a failure of this sort, you have to ask why the component failed. It didn’t fail on its own, there was some stress that caused it to fail. Resistor stresses are very well known. When they fail with an over-heating indication (burn marks, etc), then the over-stress has to be questioned. You can bet that it comes from having too much drive into the equipment. At that point, you then need to ask where that drive came from, then start looking at everything in the overall system for the reason. You will most likely be surprised where it comes from. The fact that this has happened twice is an excellent indicator that it is somewhere in the system that has yet to be properly investigated. I would encourage you to better look into the components to find out just what is going on. To put it another way, I have reviewed enough KPA500 log files for this scenario to have an excellent feel for where these problems arise. It is never the amplifier. Good luck with your station. I hope you find the issue without too much difficulty. 73, Jack, W6FB > On Apr 27, 2019, at 5:48 PM, Dave <rocke...@gmail.com> wrote: > > Hi Jack, > > No indication suggests the radio is putting out excessive power. To prove the > point I used two different radios (Flex 6600 and Anan 7000dle. Anan has PA > power calibrated.) > > Flex Power Genius XL has lightning fast protection and never shows spikes. > Array Solutions Power Master II does not show spikes. It is NOT a spike issue > but rather the amp thinks input power is excessive. It thinks 10 watts is 79 > and 21 watts is 191. > > Something is amiss when using the amp on 80 meters with tuner in circuit. > Remote app says max power of 1620 but I run about 1250 max. All other bands > are resonant. > > Another symptom is when going from standby to operate the noise floor drops 3 > dB on bands where the tuner is bypassed. > > The 3 watt resistor was added after initial design of Rev C filter board. It > is in the circuit that feeds RF to the on board frequency counter. This is on > the input side of the filter board. Maximum power I run on any band is 35 > watts. > > I am sure when the log file is reviewed it will show it is not spikes. > > Dave wo2x > > Sent from my iPad > >> On Apr 27, 2019, at 8:28 PM, Jack Brindle <jackbrin...@me.com> wrote: >> >> They are going to want to know what is going on with the input power. The >> burned resistor (twice!) is a very good indication that there is indeed too >> much power flowing into the KPA’s front end at times. It is quite possible >> for any transmitter to put out more power than spec at times, especially if >> it is not properly calibrated. >> There are many rigs that as-designed have a bad tendency to overshoot >> drastically on key-down, then settle to the power they are supposed to be >> putting out. An analog wattmeter will not be fast enough to show the >> problem, but the amplifier’s input definitely sees it. >> >> You need to get them to fix the KPA’s input circuit, but you should also >> investigate your transceiver to find out why it is overshooting at times. >> Perhaps it is in need of a fresh calibration or something else might be >> going on. >> >> 73! >> Jack, W6FB >> >> >> >>> On Apr 27, 2019, at 4:20 PM, Dave <rocke...@gmail.com> wrote: >>> >>> I can wait until tomorrow. Won’t bother them on Sunday. >>> >>> The symptom this time is different than last. Last time was amp acting like >>> tuner not tuned. This time showing excessive input power even though actual >>> power is fine. >>> >>> Let’s see what happens. >>> >>> Dave wo2x >>> >>> Sent from my waxed string and tin cans. >>> >>>> On Apr 27, 2019, at 7:17 PM, Don Wilhelm <donw...@embarqmail.com> wrote: >>>> >>>> Dave, >>>> >>>> Time to contact supp...@elecraft.com. >>>> Unfortunately, they are only open for the next 45 minutes (unless someone >>>> is working late), so be patient while the support folks enjoy their >>>> weekend. >>>> >>>> 73, >>>> Don W3FPR >>>> >>>>> On 4/27/2019 6:48 PM, rocke...@gmail.com wrote: >>>>> The input too high only happens into a non-resonant load (tuner in >>>>> circuit). >>>>> Also noticed on 20 now when tuner is in operate there is a 3 dB drop in >>>>> noise floor. >>>>> This is the second time the 3 watt resistor has desoldered itself from the >>>>> board and both times the resistor is discolored. >>>>> Only one RF path from radios through switching into amp input. Amp output >>>>> feeds a 1x4 antenna switch. No other radios transmitting in near >>>>> proximity. >>>>> Definitely something failed on filter board. >>>>> Dave wo2x >>>>> -----Original Message----- >>>>> From: Paul Baldock <p...@paulbaldock.com> >>>>> Sent: Saturday, April 27, 2019 6:21 PM >>>>> To: rocke...@gmail.com; elecraft@mailman.qth.net >>>>> Subject: Re: [Elecraft] KPA-1500 input too high >>>>> Try it in to a dummy load. >>>>> - Paul >>>>> At 02:48 PM 4/27/2019, rocke...@gmail.com wrote: >>>>>> Hi All, >>>>>> >>>>>> >>>>>> >>>>>> KPA-1500 s/n 423 >>>>>> >>>>>> >>>>>> >>>>>> Operating 80 meter SSB running 20 watts drive with tuner engaged for >>>>>> about >>>>>> 1240 watts out PEP. Remote app shows maximum power handling of 1620 >>>>>> watts. >>>>>> >>>>>> Out of nowhere I got an input power too high alarm @ 191 watts! The >>>>>> radio is capable of 100 watts out max and verified is set to 20 watts. >>>>>> >>>>>> >>>>>> >>>>>> Set tune power to 10 watts. >>>>>> >>>>>> Meter in amp during standby reads 10 watts. >>>>>> >>>>>> Switch to operate and immediately get input power too high alarm @ 91 >>>>> watts. >>>>>> >>>>>> >>>>>> >>>>>> Switch to 20 meters (resonant antenna). No issue - 10 watts tune is >>>>>> approximately 400 watts out with no error. >>>>>> >>>>>> >>>>>> >>>>>> Any ideas? >>>>>> >>>>>> >>>>>> >>>>>> Dave wo2x >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> ______________________________________________________________ >>>>>> 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 >>> ______________________________________________________________ >>> 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
