Thanks for you comment Dalecoy.
Replacing the potentiometer on the MK. 2 anemometer.I have just completed replacing the wind-vane potentiometer on my son's Mk. 2 anemometer. It now works, so we have a spare - better than throwing it away and much cheaper than a new one or a Davis refurb!
The job is much more difficult than on the Mk 1 (see previous post): Here's how I did it.
(1) Remove the support tube from the pole clamp fitting (small Phillips screw with nut).
(2) Screw a wood screw into plastic tubular cable clamp in the bottom end of the tube and pull it out to free the cable.
(3) Remove the anemometer cup spindle assembly (remove single Phillips screw and click it off).
(4) Disengage the support tube from the anemometer head and slide it up the cable out of the way.
(5) Remove the wind vane from its spindle (Allen key)
This exposes the potted electronics at one end (with the top of the speed sensor pickup coil just visible across the centre) and the nut holding the wind vane potentiometer at the other.
(6) Remove the nut and washer holding the potentiometer.
(7) Using a small G clamp or a vice, with the cup end of the housing fully supported against a flat plate or piece of wood, GENTLY press the potentiometer and electronics assembly out (towards the cup end). The potting compound is quite soft and no great force is needed.
(
To replace the potentiometer, it is then necessary to get at the three soldered terminal pins that attach the round circuit board to it. This means CAREFULLY picking all the the potting compound out to expose the terminals and the rest of the circuit board components. There are no 'loose' wires to catch in, so this is not too difficult. I used a pointed kitchen knife.
(9) For ease of working, I then unsoldered the 4 wires from the printed circuit board, but this isn't essential.
(10) If you have an de-soldering vacuum tool, then un-solder the three large terminals (2 one side and one the other side of the central wind-speed pickup coil. If you haven't got one (I hadn't), life is harder! I cut the top off the faulty Davis potentiometer to expose the other ends of the 3 terminals seated in the ceramic top plate of the pot. I then drilled them out with a 1.5 mm drill, until the circuit board dropped off. This left protruding pins that I could solder to for the next operation.
(11) The 3 pins on the replacement potentiometer were spaced differently to those on the Davis original, so it couldn't simply be soldered into the same pin holes pn the board. Instead, I soldered short 3/4" lengths of thin flexible insulated red, green and yellow wire between the circuit board pins and the appropriate potentiometer pins, arranged so that they could collapse without shorting when the circuit board was pressed down against the potentiometer. Fortunately, the replacement pot was slightly thinner than the original, so the overall length of the resulting assembly was about the same, in spite of the wires sandwiched between the board and the pot. (This is important, to maintain a gap between the rotating cup magnet and the pickup coil).
(12) Resolder the 4 cable wires onto the circuit board terminals (if previously removed).
(13) Clean any residual potting compound from the housing bore (leaving some to hold the small drain tube in place) and slide the potentiometer/circuit board assembly into the housing.
(14) Replace and tighten the washer and nut on the potentiometer stem to hold everything in.
Since the circuit board is no-longer rigidly fixed to the pot., it will, in due course, need to be re-potted to hold it in place, but I haven't yet done this. I need to first find a suitable 'soft' potting compound. Everything nevertheless works again and the vane registers correctly at all compass points.
Phew!