Shark Shield on-off knob problem fixed

 Short version:
There is a magnet that is part of the On-Off knob that got corroded and the unit wouldn't stay on; Shark Shield provided a replacement knob and O-rings which should, if the screw holding it on is fairly tight, keep water from getting under the knob in the future.

Long version: 
A few weeks ago, after using my Shark Shield Freedom 7 for about 2 years, I was launching and couldn't get the device to turn on, even after turning the on-off knob several times.  It felt like there was grit under the knob (I'd had a serious roll in the sand late last season, and though I'd rinsed the unit several times since, I thought maybe some of the fine Carmel sand was still under the knob.)  so I took the screw out of the top and took the knob off, brushed off some dark particles on a small round magnet that is molded into the bottom of the knob, and put the knob back on.  But I still couldn't get it to turn on for more than a few seconds at a time.  I figured I had little to lose, so I gave the unit (not the knob) a sharp rap with my knuckles after I'd turned the knob on, and it stayed on all day.   But the next time I went out, I'd hit it but it would stay on random lengths of time from a few seconds to a hour or so.
   So I took the knob off once more and examined the underside again, and realized that the magnet was corroded/disintegrating and probably had swollen in the process and caused hairline cracks in the knob.
    I e-mailed Shark Shield in Australia and described the problem and requested a replacement knob, which came free in about a week from a Minnesota address.  I put the new knob on and the unit worked fine.  I'm pretty sure the magnet operates a switch within the sealed unit when the knob is turned so the magnet is in the proper position, and the corroded magnet wasn't powerful enough to trigger the switch, but had just enough force to barely keep the switch in the on position most of the time.
   Importantly, the new knob came with two "O" rings, one large diameter, one small.
The large one fits into a groove in the case under the knob, and the smaller one under the small plastic "washer" that the screw goes through to hold the knob itself on.  I hadn't noticed the original rings because they are the same red color as the knob So it appears that the O rings are meant to keep water out from underneath the knob so that the magnet doesn't get corroded, and, possibly, so that water doesn't get into the case, though I would think there'd be other O rings inside the case to keep water from entering if there is any opening under the knob, which I doubt. 
   I can imagine that if the knob screw comes un-tightened just slightly, some water can get past the O rings and begin to corrode and lead to the problem I had.
    It's also possible that I torqued the knob somehow in my rollover or by striking it some way and created the hairline crack which led to water intrusion.
     The manual I got with the unit says nothing about maintaining the knob, though it does say to rinse the unit thoroughly (Which I did, maybe too thoroughly, because I used the "fan" setting on my garden hose-end sprayer to spray into the space between the knob and the case- maybe forcing water past the large O ring.).
     And while I will probably just gently bucket rinse the unit from now on, and even though I might wonder whether water is getting past the O rings, I don't think I'll be unscrewing the knob to check, because that might create a problem where none exists.  Right now, I've got the screw tightened to the point where the knob will turn, but not real easily. I'll just trust that it should work well from now on, and if it doesn't get another knob and maybe silicone grease the O rings and dielectric grease the magnet.
      Shark Shield didn't give any explanation or instructions  with the replacement knob and rings, but they were very quick to replace the part when I brought the problem to their attention.
     

Thanks for sharing, will bucket rinse and not hard spray, if I rinse at all, I am lazy sometimes.

Thanks for the detailed info.

I guess I've been lucky, but my SS is pretty old (can't remember exactly, but at least 5 years) and I (unintentionally) abuse it all the time, having rolled it on the beach, dragged my kayak onto the sand with the SS thru the scupper hole, etc., and I always spray it off with as much force as I can muster. The only things I've noticed is that it has about 15 minutes less run-time than when new, and there is getting to be a fair bit of corrosion on the recharge prongs.

Might have to start being more gently in the washing phase...

Yeah, MDoka Matt had the same issue with his Gen 2 SS.
They just sent him a replacement knob and it solved the problem easy peasy.

My Gen 1 SS never had an issue until the day it stopped charging, after 7 years of abuse.
I do tend to baby the gen 2 I have now much more than I used to with the Gen 1.