What is the high current alarm set at? Are there the correct number of turns on T4? (check against the illustration in the assembly manual) Perhaps there is a problem with the bias system. Transistors Q11 and Q13 should probably be changed as well as the finals if there is a problem with the PA stage. You did not say what the set serial number is. I am not sure if that might make a difference with troubleshooting help, but it could.
- Jim, KL7CC On 10/13/2012 3:29 AM, w7asa wrote: > This K2 was a bought from someone on the internet as a working unit & etc. > Once received, it blew the finals in about 2 - 3 hours of QSO time. I > really like the K2 but it looks it's mine to solve. I've done a lot of > radoi building and RF troubleshooting down through the years, and have > looked for all the usual suspects of shorts, debris shaken loose during > shipment & etc. > > BTW: The condition of the board and mounting hardware for the finals and PA > bias transistors STRONGLY indicates that they've been changed more than a > few times *before* the rig reached me . . . so , in all probability, I was > probably the only one surprised by it's sudden demise. > > Here's what I am seeing: > > It has fried three sets of finals in two weeks - I changed them per the > manual twice ( am a glutton for punishment ) and VERY carefully re-checked > my work and metered for shorts each time. After =< 2 to 3 hours of 'normal' > operation each time, the finals blew. This happened on three separate bands > with an SWR of 1.2:1 (on average) at 10 Watts indicated both on my SWR/power > meter and the K2 digital display. I did not notice a current warning during > the last two failures and now am not certain whether I did during the first > failure. > > Most recently: - I had finished the most recent ragchew then switched to > calling CQ using a Vibroplex (as always) and heard a small 'crack' of a > transistor case rupturing when immediately the 3 Amp automotive fuse in my > power cord blew. The smell told me where to look. > > This is a relatively simple circuit and it seems to me that there is not a > lot to go wrong: T4 with bad insulation ? Something in the common parts of > the LGP/Band switching but not band specific? I am mystified why it would > run flawlessly for a few hours of CW then let the smoke out. > > Anybody have ideas? I have a ton of Elecraft accessory boards on the way and > that's a lot of assessories for a radio that drops dead continuously. > > >> Ray > W7ASA ..._ ._ > > > > -- > View this message in context: > http://elecraft.365791.n2.nabble.com/K2-Finals-Chronic-Blow-Outs-tp7564052.html > Sent from the Elecraft mailing list archive at Nabble.com. > ______________________________________________________________ > 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
