The lack of the 3v3 LED is probably a big hint. I’d prefer to buy the board instead of repairing it, if it was efficient, any pointers? I suppose I could contact customer support, but …
You need to find the 3.3V regulator and replace it. Alternately, if you have nothing to lose (busted is busted, so there’s not a lot of risk to busting it more), you could buy a 3.3V regulator board (like from Polulu, that takes 24V in, since it appears 24V is nearby and I’m assuming that LED still lights up) and hook it in. You’d need to find a point on the 3.3V rail you could connect the replacement regulator to, but in all probability either one side of R2 is on the rail and the other side is feeding the LED which is tied to ground, or the LED is on the rail draining through R2 to ground… Unfortunately, regulators don’t usually just die spontaneously, they die because they’ve been overloaded. If you replace the regulator you might just discover something else is actually what’s busted and the board won’t work even with a replacement regulator. If you inspect the board really carefully you might find evidence of an overheated part.
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Ya, its a TI 54336A switching regulator. Could be the inductor gone too, they are a bit known for dieing. I was thinking of, indeed, basically patching in a 3.3V buck convertor (the input is 24V, linear is gonna be real hot) in there. The other option is, well, it is just 2 steppers and a limit switch, could actually make a new controller fairly easy. But I already have so many projects…
Yah, using a replacement power supply (and disconnecting the chip … it was trying to sink the other power supply) and the wash works totally fine and doesn’t draw untoward power, etc (about 18 mA on the 3v3 supply). I’ll slap in a buck convertor of some sort and call it a day. The chip is a power pad is a is a serious PITA to remove (beyond my skill to do without likely damaging the board), so I’ll leave it in place unconnected.
I guess while I’m at it I’ll check why the impeller is making a rukus. This wash has seen very light duty and I’m not impressed. The build quality is great, but the actual reliability, for me, has been dismal and they won’t service it or sell parts etc.
I see traces of liquid spilled over the board and also some solders oxidation.
If water was spilled over the board while 24V applied, it can create electrochemical corrosion and some traces/vias can be broken or resistive bridges can form between pads.
My experience is that in 85-90% of cases with such boards the failure could be located visually or by using simple multimeter.
I would suggest first you clean your board in pure IPA (soak it for 30 minutes in IPA, then use brush to clean it thoroughly and dry it at thet). Inspect the solders with magnifying glass or microscope. If possible replace the TI 54336A regulator (it takes less time to replace it than to prove it’s working). Personally I’m pretty confident that this board can be repaired and fully recovered
Well now you tell me 
By the time you posted, it was too late, chip disconnected. I do see the spots you refer to, but there is now way this was exposed to water since purchase; it has been in a very tightly controlled environment, and on top of that, the PCB is very inaccessible. However, I would have been willing to give it a try.
Instead I’ve gone and added a secondary DC-DC convertor on a little daughter card, and it now works like a charm.
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