Mike,
How did you check the value of the resistor. If you used your DMM while
it was in-circuit, then you have an open L33. The BFO would oscillate,
but the range would be restricted as yours is or more narrow.
First thing, check capacitors C173 and C174 to be certain you have the
correct values installed. Those blue capacitors with the yellow
printing on them are difficult to read, so use a magnifier and lots of
light.
Then check D37 and D38 to be certain they are oriented correctly - the
slightly angled side is the "rounded" side.
Make certain RP6 is well soldered - reflow with a hot iron (750 degF)
and apply a bit of extra solder - you really one need the flux. The
iron dwell time should be about 3 seconds, but watch for the solder to
flow out onto both the solder pad and the component lead to assure good
soldering - up to 5 seconds dwell will not hurt anything.
Then when doing the BFO Hi and BFO LO frequency checks make sure RP6 pin
7 goes to quite near 5 volts and also quite near zero volts.
The above are the easiest items to check.
Keep in mind that the resistor which holds L33 is really an insulator,
it serves no electrical function.
You are correct that a bad BFO crystal could cause the problem, but to
change them (change them as a matched pair), you have to lift L33. Not
too bad is you are careful, leave the leads connected to the resistor
leads, heat the solder pad and pull the resistor lead out - repeat for
the other side and lift L33 and the resistor off as an assembly.
So try the easy stuff first, and if that does not cure it, contact
Elecraft Support and request a pair of BFO crystals and a new L33 and
5.1 meg resistor to replace them.
73,
Don W3FPR
On 9/30/2017 5:40 PM, Mike Maiorana wrote:
Thanks Don.
I triple-checked the inductor wires and they are well soldered to the
pads. I also verified the value of the resistor across it, 5.1 Mohms.
I reflowed the solder anyway, but no change in the BFO frequency range.
If L33 wasn't connected would the oscillator even run?
If one of the two crystals was bad (or not soldered properly) would
you also see a reduction in BFO range?
What about if one of the varactors had failed?
Any further advice will be greatly appreciated.
Thanks and 73
Mike M.
KU4QO
On Sat, Sep 30, 2017 at 9:57 AM, Don Wilhelm <donw...@embarqmail.com
<mailto:donw...@embarqmail.com>> wrote:
Mike,
The inadequate BFO range is usually a result of the L33 toroid
leads not being well soldered. The toroid wires are very fine and
sometimes are not visible to the naked eye, so use magnification
to examine them. When re-soldering, use a pointed tool to bring
the fine toroid wires down onto the solder pad instead of further
up on the securing resistor lead.
For adjusting the 4 MHz Reference Oscillator (that has nothing to
do with the BFO range), refer to the K2 Dial Calibration article
on my website www.w3fpr.com <http://www.w3fpr.com> for the most
accurate method of adjusting the Reference Oscillator.
Be aware that the 4 MHz Reference oscillator can drift in normal
operation, so soon after adjusting it, run CAL PLL and CAL FIL
while it is still "on frequency". That oscillator is not used in
operation for the K2 frequency display. In other words, simply
adjusting the 4 MHz Reference does nothing for normal operation.
73,
Don W3FPR
On 9/30/2017 9:35 AM, Mike Maiorana wrote:
Hello all. I have a K2, 6000+ serial number, that I'm trying
to get working
correctly. Unknown history. A quick test showed the filters
were not
properly adjusted (could hear both sidebands of carrier on
some bands). I
thought it would be best to do a top-down alignment.
I adjusted the 4 MHz oscillator, verified the PLL reference
oscillator
range (12.43 kHz), VCO test and VCO alignment. No problems up
to that
point.
I'm having an issue at the BFO test. The BFO high frequency is
4916.04 kHz
and the low frequency is 4913.82 kHz. That's a difference of
2.19 kHz, well
below the 3.6 kHz stated minimum.
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