[Elecraft] K3 Freq jumpnig when cold (50F or so)

[Bill Coleman]

Have our club's K3/100, serial # 67xx.   When it is cold (FP=11C  52F ),
increasing the frequency using  VFO A or VFO B causes a 1MHz jump DOWN in
frequency.  When reducing frequency the failure is much less frequent and it
will also jump down 1 MHz.  At times while tuning up in freq there are some
relay clicks - usually 2 -  but no frequency jumps.

 

BOLD = actions / changed made

 

More observations:  

.          I picked up the radio, we are having an unusually warm spell here
in NY.  The rig seemed to work perfectly.  

.          I put it in my fridge.   FP temp = 11C (52F)  Fails frequently.
Always a 1 MHz jump down.   i.e on 7.125 the fail sets the freq to 6.125.

.          With the rig on 80M, band down press yields 100.00MHz.   If I
manually enter 1.80 it is on 160M, band up = 80M, band down is back to
100MHz.  Per the setup, 160M and 6M are excluded from up/down sequence.

.         Rig warming up, FP = 21C   Operates normally

.         Back to the fridge, FP=12

.         Starting on 40M, increasing VFO A will cause switch to 6MHz.
Pressing Band UP gives 80M not return to 40M.

.         Similar to above, starting on 30M the rig jumps to 9MHz, band UP
gives 80M

.         Again similar, starting on 20M, jumps to 13MHz, band UP gives 80M

.         Occasional jumps to 3xxMHz - difficult to see pattern

.         Rig up to FP=19C  working normally

.         Backed up the CONFIG, performed EE INIT, restored CONFIG

.         Cooled off the rig FP = 12

.         Not seeing the 80M band DN going to 100MHz.   Not seeing random
3xxMHz

.         Still have frequent jump down 1MHz

.         Removed Front panel, removed DSP board. Reseated both twice.

.         Working normally at room temp

.         Cooled off the K3  FP = 13

.         Failing as above, 1MHz down shifts

.         FP = 15+ seems to be working OK

.         Cooled off the rig

.         Exercised frequency control and band changes via RS232 - this rig
is also operated remotely - no failures noted 

.         Other freq jumping as above occurring via manual tuning.

 

Net:  EE INIT seems to have "cured" the 80M band DN to 100mHz & random shift
to 300MHz.

 

Sorry for the loooong post.  What y'all think?   Trip to California - or
poor man's fix: turn up the heat in the club's shack (it is unheated!)

 

I'm a tiny bit tempted to swap front panels with my personal K3 - very tiny.

 

THX for reading,   73  Bill N2BC