Our echo sounder has a rotating armature. It got stuck a couple of weeks ago but worked after a tap or two. This afternoon it was stuck again, obstinately so.
After dinner I took it apart. The plastic case and bezel are very brittle but inside it looks like new. The O ring seal must be excellent.The back comes off by undoing four captive screws.Inside, these connect to four posts which also unscrew. There are also two additional screws. The PCB is then held on only by the two knobs.
The knobs come off by popping the pale grey covers off and undoing a nut. They have their own O rings which just pull off.
I knew it must be either the armature motor or the armature itself. The armature did seem stiff so I sprayed it with WD40 to clean it. After working it round a few times it seemed to spin OK so I tried turning it on. Bingo!
I put it back together again and reinstalled it and it works perfectly.
The knobs are interesting. They have a brass compression fitting so you fit them and do the nut up and then you can adjust the pointer on the knob to the right place before tightening. A really nice design.
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