+++++++++++++++++++ Also See K2 Low Receiver Sensitivity +++++++++++++++++++ From: "Dieter Kuckelkorn" Subject: [Elecraft] Low sensitivity of K2 receiver / solution Last week I was asking for advice concerning the low sensitivity of the K2 reciver. With the help of Gary AB7MY from Elecraft, Tom N0SS, Don W3FPR and John K7FD (who had the same problem) I found the solution and want to keep everybody informed. One of the crystals of the 5-pole-filter (X7) was bad. Internally it had a short to the case. Actually this is quite easy to find out with a DMM: Look for connections from the crystal pins to ground, if the filter is already soldered in. A short can by caused (as in my case) by a bad crystal delivered by the manufacturer or by the excessive use of solder which causes a short between the leads and the case of the crystal. To find out what causes the short you have to solder out the crystal. Unfortunately, you have to replace SEVEN crystals, if one is bad. What Gary told me: To find out whether there are further problems with the K2, you can replace a bad X7, X8, X9, X10 or X 11 by a 0.01µF capacitor. You'll get less selectivity, of course. So it's only a solution for a short while during troubleshooting. But, as Gary has pointed out, it is far more common that low sensitivity is caused by poorly tinned toroid leads, mistakes while winding the toroids, or cold solder joints. Again, thanks to all the folks who helped me. vy 73, Dieter DL1DBY Stamford CT ++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Sun, 25 Mar 2001 20:42:31 +0100 From: "J. Ellis" Subject: Re: [Elecraft] K2 #1920 Lives! Sort of Doug Person wrote: > K2 #1920 is complete. The transmitter seems to be working just fine. > However, while in the Part II alignment, I was able to copy nice signals on > 40. Not anymore. Doug, I would look for some kind of very fine less than hair thin solder bridge. You might try "tapping" or pushing the board in various areas with the non-conductive handle of a small screwdriver to see if by mechanically jarring it (gently :-), you can detect an intermittent connection. The other thing to check is try reheating the connections to the toroids. You may have one where the enamel is just so close to the solder pad that sometimes it makes and then sometimes it doesn't. Pay special attention to T-6 if the preamp seems to act more like an attenuator than a preamp. (check it with the pre/att switch) Make sure VFO is still working, check the BFO, check the RFCs that utilize toroids, It's my understanding that most of these kinds of problems can be traced to not getting sufficient enamel off the toroid leads. Gud luck, 73, John, NP2B K1/426, K2/1645 - -- Jeanette & John Ellis (NP2C & NP2B) P.O. Box 24492, Christiansted, St. Croix U.S. Virgin Islands 00824-0492 tel (340) 773-9643, fax (340) 773-6574 website http://www.viaccess.net/~jellis When responding to e-mail, please send to jeanette at atthehelm.com or john at atthehelm.com +++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Sun, 25 Mar 2001 17:18:58 -0500 From: "Doug Person" Subject: Re: [Elecraft] K2 #1920 Lives! Sort of John, Thanks for making me think to look at simple explanations first. It was a slightly cold joint on D3. I just starting pushing and poking on the components in the preamp and BANG! Suddenly 40 came alive with S9+20 signals. I just carefully reheated D3 (from the top to avoid disassembly) and it works like a champ. And wow! what a receiver. Now to finish the rest of the receiver alignment. Thanks, Doug -- W4DXV ++++++++++++++++++++++++++ From: "Garth Hitchens" To: Date: Tue, 29 Jan 2002 10:33:37 -0800 Subject: [Elecraft] FYI - Low sensitivity / VFO (aka Gary Surrency Rocks) I just have to rave about the support I got from Elecraft, and point out a potential problem for others. I built a K2 months ago and always felt like it wasn't quite as "hot" a receiver as I expected, but it worked ok otherwise, and certainy well enough compared to some other rigs I had. Recently, I built the 160 module for my K2, and had problems getting more than a few watts out at the band edges, or more than 7 in the middle. I got no HI CUR warning, just couldn't drive it more than a few watts out. After a few emails with Gary Surrency I had ruled out problems in the bandpass filters, low pass filters, and power amp circuits. After I told Gary I was using a scope, he happened to mention to me during this to "make sure that you have about 2.2-2.4v p-p on TP1 (that would be about 0.78-0.85Vrms as an RF probe would measure)". Bingo! Mine had about 1/5th that value. That turned out to be my problem - I had a bad solder joint on a capacitor near the input side of the VFO buffer amp. After repairing the solder joint, not only was I able to drive 160 to full output all across the band, but I also had a much hotter RX as well (didn't need the preamp anywhere near as often!). So, if you're suspecting low sensitivity and have problems with power out on 160, measure your VFO output at TP1 with a scope or RF probe, you might have a low VFO output. Garth KG7GA +++++++++++++++++++++++++++++