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Mike, NI2S's Ham Blog

Page 19

 

08-Mar-08 - RF Board Alignment

 

The missing capacitor arrived and was installed.  Next was the initial resistance checks which were ok.  After that a series of alignment steps for the PLL, VCO, BFO and IF circuits.  Here I hit a snag.  Everything was going great until the last step - the IF alignment - No audio.  The receiver wasn't working!

 

I am not a hard core homebrewer.  The only test gear I own is an aged Fluke DMM, though I used to own more test gear in the distant past.  I don't have a lot of rainy day money lying around to run out and by a signal generator, a frequency counter and maybe a nice oscilloscope.  In addition, since this is the first kit I've built in 20 years or so, there is a heavy coating of rust on what skills I had to read a schematic, and troubleshoot a broken circuit.  But - here it goes......

 

I browsed the Elecraft website looking for troubleshooting tips and found Tom Hammond, N0SS's tutorial on "Cheap and Dirty signal tracing".  So, I built his cheap and dirty signal tracer.  Cheap as dirt, because all it is a 100pf cap placed in line with a working antenna. The Cap becomes the probe.  How cheap and dirty can you get!?

 

First, using the suggested test points by N0SS, I got no signal at any of his recommended test points.  Next I turned to the schematics and tried a few points at random more or less 'in the middle' of the receiver circuit.  I found a signal at jumper W2, and started tracing from there.  This ultimately led me to discover two missing parts - Z6 and C167.  What is Z6?  Oh, nothing much except the receive mixer!!

 

So I installed Z6 and C167, and I now have audio in the headphones.  However, the audio is quite low.  Even though I was able hear well enough to complete all of the alignment steps, I am going to pause here until I am satisfied the audio issue is fully debugged.

 

11-Mar-08 - Talked to Elecraft about the low audio.  They suggested I finish the kit and then troubleshoot the low audio after the rig is fully aligned.  So...onward!