Hi Don, Success!!! I mostly followed your advice--I say mostly because I got diverted when I found a clue. I would still be searching without your insights and expertise, however.
I was getting about 150 mv out of pin 4 of u7. I traced it to pins 1and 2 of J6, which was still hot on the scope through the secondary winding of T1 ON THE FILTER BOARD but was dead upon arrival at pin 6 on the return leg. This sent me on a merry chase of testing all the relay solenoids for continuity, and their contact leads. They all checked good so then I leapt at the conclusion that the controller IC was at fault. I tried resetting it to factory default but no apparent change resulted. So, I went back to the scope and finally found the exact dead end: C15 was wrongly mounted. Somehow, I misread the silkscreen hole indicator, I'm embarrassed to say. Anyway, I resoldered it in the right holes and, instantly, robust CW screamed at me. I'm thrilled and humbled. Thanks again, Don 73 Les KE7SLX On Monday, August 18, 2014, Don Wilhelm <[email protected]> wrote: > Les, > > If you can get at least 200 mV peak to peak out of the Pre-Mixer bandpass, > the VFO level is OK. > The VFO and band module xtal oscillator are mixed in U7 and the output of > that mixer (after the bandpass filter) is applied to U1 pin 6. > > If you find you need to check for loading of the U1 output, lift one lead > of C22 to isolate it. > > 73, > Don W3FPR > > On 8/18/2014 6:08 PM, Les Garwood wrote: > >> Hi Don, >> >> Extremely helpful and encouraging; thanks. Actually, I was able to get >> the trimmers set pretty well, i think, using a strong signal source. But >> I >> will make the measurements you recommended. >> Right now, I suspect either low VFO output or something is pulling down >> the >> gain of U1. >> >> Les >> On Aug 18, 2014 3:00 PM, "Don Wilhelm" <[email protected]> wrote: >> >> Les, >>> >>> Yes, the NE612 should show plenty of gain. When it does not, the usual >>> reason is little or no oscillator signal to pin 6. >>> >>> The Pre-mixer Bandpass filter must be aligned before you will get much of >>> a signal at U1 pin 6. >>> >>> Since you have a 'scope (hopefully with a 10X probe), I will give you an >>> alternate method of tuning the Pre-Mixer Bandpass filter. >>> >>> Since you have the 4 band board, you must follow the proper band order - >>> adjust 15 (or 17) meters before adjusting 20 meters, and likewise adjust >>> 30 >>> meters before 40 meters. >>> Make a check before starting - align all the slots in the trimmer >>> capacitors parallel with the long edge of the band board. Then check the >>> activity of the crystal for each band - put your probe on band board P1 >>> pin >>> 4 and not the amplitude of the signal as you switch through the bands - >>> you >>> should have greater than 200 mV peak to peak. The position of the >>> trimmer >>> slots when tuned should be no more than 30 degrees from the center >>> position >>> if your toroids are correct. >>> >>> Then switch to 15 (or 17) meters, and with your probe on P1 pin 6, adjust >>> the Pre-Mixer trimmer caps for 15 meters for the maximum amplitude. >>> Switch >>> to 30 meters and do the same for that bands trimmers. Do the same for 20 >>> meters and 40 meters. You should be able to get 200 mV peak to peak >>> there >>> on all bands. >>> Remember that your 'scope probe will load the Pre-Mix filter a bit, so >>> the >>> trimmers to the right of the filter will not be at their optimum setting, >>> but it will be enough for receive - you will set the optimum position >>> when >>> you adjust for transmit. >>> >>> You should check to see that the Pre-Mix signal is getting to U1 pin 6 - >>> if it is not, suspect the coax link on the bottom of the board between J9 >>> and J10. >>> >>> Once you have a good signal at U1 pin 6, you should see that the output >>> at >>> pin 4 is much greater than the input at pin 1. >>> >>> 73, >>> Don W3FPR >>> >>> >>> > ______________________________________________________________ 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 Message delivered to [email protected]
