VFO Encoder doesn't change frequency

[TI2/NA7U]

I have a very similar problem to what G0NIG posted about a year ago. Last digit of the frequency flickers but nothing else changes when spinning the dial. This applies also to the menu. I followed along with what Nidge had done with Don's help and found some similar measurements, others not quite. The final measurements were resistance measurement with and without the CB MCU installed. After re-installing the MCU the encoder again worked, perfectly! At each step of re-assembly I test the VFO again and it still worked, ... until I put in place the front panel and had only tightened the screw holding the encoder. Now it is stuck again. I figured  that I'd re-seat the MCU again, and clean the contacts, but no joy.

My measurements on U3 on the FP board are:
Pin 14, .09v, Pin 15, 4.2V, Pin 7 3.4v.

Note: when the encoder was again briefly working these voltages were the same! In Nidge's original thread Pin 14 was highly suspect because of the low voltage, but when the encoder was working in my K2 the voltage was still low.

I've checked continuity of ENC A and ENC B all the way back to the MCU, it's good.

Resistance from each of the 4 encoder pins to Gnd:
With the CB not in place -
   Pin 1 - 24K, pin 2 - 618K, pin 3 - 617K, pin 4 - 538 K
With CB in place, and with and without the MCU plugged in the measurements don't vary -
   Pin 1 - 3K, pin 2 - 581K, pin 3 - 579K, pin 4 - 507K

Open to ideas.

73,

Casye

[John K3TN]

I had this problem early with my K3 and was told it is usually one of two things: (1) a board seating problem or (2) a temperature sensitivity problem. Since it occurred when my factory built K3 was only a few months old, they said to send it back for warranty repair.

Of course, when it got to Elecraft the problem did not present itself. They did temperature cycling and the problem did not occur. Likely the shipping jostling seated the board again. Worked fine when I got it back, but the problem did reappear once. Reseating the boards again cured the problem again.

John K3TN

[TI2/NA7U]

Good suggestions John. I don't know how the board connections work in the K3, not having one. In the K2 there is only one board connection involved, the FP board to the CB and it uses long pin plug/jack to accomplish this. It would be very difficult to jostle it loose. Anyway, my take on it was that the MCU was the part not making a good connection as the VFO started working when I took it out and put it back in during the course of taking measurements. Up to the point where I had everything back together except the faceplate it was still working. As soon as I put the faceplate in place and only tightened the screw holding the encoder in place, back to square one. Extracting, cleaning the pins, replacing the MCU now has no effect.

Could be some other component(s) has failed.

73,

Casey, TI2/NA7U

[Don Wilhelm-4]

  Casey,

"As soon as I put the faceplate in place and only tightened the screw
holding the encoder in place, back to square one"

That is usually an indicator of a bad solder connection.  I would
suggest reflowing the solder on the front panel board and the mating
connector on the RF Board.

73,
Don W3FPR


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[TI2/NA7U]

Bingo Don! Check the simplest explanation first. It actually wasn't a soldering problem, though solder was the solution. One of the encoder wires has a micro-crack in it that I'd overlooked before, or maybe it widened when I was moving things around, but it jumped right out at me when I took off the FP last time. All fixed!!

Thanks es 73!!