Well, I took my lack-of-sensitivity analysis to the next stage and performed the Signal Tracing checks, as described in the Elecraft K2 Manual. Injected the 0,14Vrms into the antenna connector when appropriate, and kept the overload diodes (D40,D41) disconnected.
In short, the DC voltages are a little low but probably close enough to normal, except U12 pin 5 (AGC) which measured 3.5V rather than 5.0V. All RF voltages appeared reasonably close to the K2 suggestions, up to and including U12 pin 4 (U12 input). The pin 4 voltage was 2.0V rather than the suggested 0.4-0.8V. However, the output signals from U12 seem to be nonexistent: U12p8 is 0V at all times, irrespective of the signal level injected into the antenna terminal. Subsequent signals are zero, as well (U11 input through pin1, etc.). Again, any suggestion on a plausible cause - a failed component or bad soldering? Has anyone run into this before, and have suggestions to try out? 73 - Kristinn, TF3KX TF3KX wrote: > > Hi - I am in the process of constructing my K2 and have two problems that > may or may not be related. > > Problem 1: Low, almost nonexistent RX sensitivity during Alignment II. I > can manage to copy a carrier from my MFJ antenna analyzer and I have used > this to verify that IF and input circuits are peaked. Injecting this > signal into the antenna terminal I can also verify that PRE and ATT work > as expected, as well as the crystal different filter bandwidths. Using an > IF carrier from the MFJ I have poked a low level signal into various parts > of the IF chain. An interesting thing is that I hear this signal much > weaker in the K2 audio when I touch it to the INPUT of IF-amp U12 (MC1350) > than to its OUTPUT. In other words, that IF amp does not amplify, but > rather attenuate the injected signal. I have re-checked all connections > around U12, re-flowed the solder, checked T7 and removed the overload > diodes D40 and D41 - with no improvement. > > Problem 2: Low 8V regulator output, 7.56V. As a result I could only > adjust the U2 pin 5 voltage to 3.60V using R1, in Alignment I. Probing > the voltages derived from the 8V supply, they are of course 5-10% lower > than expected. All DC voltages on U12 are consequently a little low, but > otherwise not abnormal. > > I plan to get a local replacement for the 8V regulator, just in case. But > does anyone have comments on the low sensitivity? Would the low 8V level > be a possible cause for this? > > 73 - Kristinn, TF3KX > -- View this message in context: http://www.nabble.com/K2--6425-low-no-sensitivity---suggestions--tp16086168p16113915.html Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
