Bill, My short answer is .. if things work after all this .. I wouldn't recommend doing anything to the circuit board after cleaning it. Instead, I'd take steps to keep the mice from ever getting into the inverter again.
Long answer... Normally, circuit boards will have been coated with a conformal protective material at the time of manufacture. For those who may not know what "conformal coating" is, it's a clear polymer liquid (usually silicone based) that's applied to circuit boards, typically as a spray (like spray paint). When dry, it forms a very durable polymer layer that's highly protective against moisture, dirt, and moisture. It's also very electrically resistant, and is accepted by Underwriters Laboratories and other Nationally Recognized Testing Labs as an insulating material. However, unless the circuit board is literally dunked in the liquid conformal material (not done for a variety of reasons), there are always going to be areas on the circuit board (under components, or the back-side of integrated circuit pins away from our view) that are not covered by the conformal coating. Even when conformal coating is well applied, urine can and will still sit on top of the coating and form a conductive path to otherwise unprotected areas of pins and leads. This is what I suspect happened here. Done properly, a distilled water / alcohol bath combination will dissolve and remove these unwanted conductive paths without harming the conformal coating. A concern I still have in this: there may be components on the circuit board that would be damaged or otherwise affected by the water and/or alcohol. Examples would be transformers, switches, relays, etc.. Good quality conformal coating materials aren't affected by water or alcohol, so this procedure is safe to use for cleaning purposes as long as none of the electronic parts themselves would be affected. Parts that have very small distances between their pins, such as microprocessors and similar, are the components most subject to unwanted conductive paths. Another aspect of the circuit board to consider are where "through-hole" parts are installed, such as relays or other components have leads that penetrate through the circuit board. Such parts can be very difficult to fully seal with conformal coating because the spray simply doesn't penetrate shadowed or hidden locations. One still must be cautious in cleaning a circuit board, as it's possible the water could penetrate the circuit board edges if it's not completely sealed, and either liquid may affect parts on the circuit board itself. As mentioned, this procedure is only if the need is dire .. and replacement isn't an easy option. I'd also be concerned with static electricity issues. I'd wager few if anyone in the Wrench kingdom has the necessary static abatement protections in place. Static electricity can and does permanently damage components, and you'll never know it happened - except the circuit no longer works. Doesn't take carpet either. Did you know you can walk across a tile floor and build up a static charge? (The voice of experience here!) Bill .. to your question: Where would you apply the conformal coating? First .. if it were me, and I were lucky enough to recover from a mouse-pee episode, I'd not use Krylon for this purpose. EVER. In fact, I'd be hesitant to use anything at all. Instead, I'd take steps t protect the hole(s) where the mouse got in so this never happens again. If it's a vent, use metal window screen cut to size, and attach the screen on the inside of the enclosure with a quality silicone adhesive, making sure not to create any electrical or other hazards in the process. (Note I said "silicone adhesive", not "silicone caulk" or "silicone seal". There's a difference.) Use fine-mesh screen. Anything larger wont' work. Mice are better than Houdini at getting in and out of tight spaces. (I've seen a mouse flatten its body and squeeze through a louvered vent with less than 3/8 inch spacing.) If you're still totally bent on trying to increase the protection on the circuit board, use a genuine conformal material from a company such as MG Chemicals, Tech Spray, or others. It will be certified to a UL Standard for the purpose. Expect to pay $20-30 for a spray-paint sized can, and it won't be available from any hardware store. Buy it from Mouser, Digi-Key, or similar sources. Get the version with the UV "tattle-tale" built in. That way, when you spray the board, you can take it outside in bright sunlight and see where the spray exists - and more importantly - where it doesn't. The tattle-tale shows up as a blue-ish or purple-ish color when viewed under ultraviolet light. Before spraying, cover all connectors, connector pins, and sockets. You *don't* want to insulate those. Following the manufacturer's instructions, lightly and evenly coat one side of the board with the conformal material, and let it dry completely. Then, check it in sunlight or under a UV lamp for even-ness of the coating. More coating can be applied if needed. Just like spray paint, two or more light coats are better than one heavy coat. When one side is done, do the other side of the circuit board. A word of caution: like spray paint, conformal coating must be applied in a well ventilated area. The board must be absolutely clean and dry. If it's not, you'll be sealing moisture and/or other contaminants into the board -- the exact opposite of the goal you're trying to achieve. Keep in mind that doing this task properly may help seal the circuit board and its components.. doing it improperly may cause more problems than you cure. My recommendation: close the doors to future mousies .. and leave conformal coating to the manufacturers. Hope this helps. Dan -------------------------------------------- On Fri, 8/16/13, Bill Loesch <solar1onl...@charter.net> wrote: Subject: Re: [RE-wrenches] Mouse pee in the SW To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org> Date: Friday, August 16, 2013, 2:38 AM Dan, et al, Once the board has been cleaned sufficiently that the inverter is no longer operating intermittently and your "hope" has been realized, when would you apply a field conformal coating? Would you choose/recommend something better than Krylon clear spray? Bill Loesch Solar 1 - Saint Louis Solar 314 631 1094 _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
