On Wed, 16 Nov 2011 21:29:39 -0600, Michael Dobony
There are also catalyzed or self curing coatings.Master bond has UV
MG's product will room temperature cure in 48 hours, or it can be
heated to speed it up.
Dow Corning makes Room Temperature Vulcanizing elastomeric and
Elastoplastic as well as solventless heat cured products.
Nordson also produces UV, Heat, and Air Dry products.
Krylon makes an electical coating this should not be confused with
clear Krylon. Board should be cleaned before it is applied or you may
trap in corrosive material. already on the board.. Plug in connectors
should be masked off to keep the Krylon out of the connectors. Use a
little electrical grease on the connectors. The grease can be obtained
at local automotive parts store. They sell it in little packets for
greaseing up turn signal and break light bulbs.
All our A/Cs have been packaged systems, but I don't think their
circuit boards ever rusted much, although we're in Phoenix. I saw
only one of their circuit boards, a defrost controller, and I don't
believe it had any protective coating on it. So is it possible your
board wasn't grounded adequately? Or would it help to attach its
chassis ground to some zinc, even just galvanized screws?
In any repair situation, it's important to fix the thing that's broke.
Any product designed to sit outside MUST be capable of withstanding
the environment. Unless you're near an ocean, your environment is likely
way less corrosive than the design/test environment.
I'd call the vendor or the installer and see what they have to say about it.
Then I'd look at how the board is configured and make sure the enclosure
isn't missing a gasket, or bent, or has an open screw hole in it.
Seal it up tight. Make sure it's dry inside when you're done.
Conformal coating seems attractive on the surface.
Of course, it's gonna void the warranty and make the board very difficult
It has thermal resistance, so any component depending on convection
cooling will be compromised.
If you decide to clean it, be aware that some components may not like
being drenched in alcohol and water.
Spraying the board in place may not be effective. You need to seal
the back and the edges of the board.
If you decide to coat it, dry it as discussed above, then dry it again.
Doesn't do a lot of good to keep out the water when the water's already
under the coating.
Still think I'd seal the enclosure first.
LOL!!!!! The panel covering it is held on with two screws and the cover has
no gasket and is ventilated to the outside. It experiences the same
atmospheric conditions as exist outside, like an open porch with open
horizontal blind style windows. To seal it up also would seal up the air
from the furnace burner.
Total reengineering and moving the board to a totally new location.
Rust on diode leads is quite surprising as even the high current diodes
with steel wire leads have a solder coating (tinned leads). Perhaps the
leads were damaged during assembly or testing and the coating was broken.
If you can turn the power off and get to the leads, I would suggest
cleaning off the rust and retinning the leads with a soldering iron and
rosin core solder.
I had our heat pump serviced last week and watched the young man as he
did his work. The circuit board controller is like yours, outside on the
heat pump and and under a metal cover that protects it from all but
blowing snow. Quite a bit of dust, but no other problems. The board does
have three 2 watt resistors that have discolored the board from their
heat. They should have been placed further from the board material.
Such heat producing devices are one good reason not to conformal coat
the circuit board. Or they need to be masked so coating material is kept
away from the resistors.
My electronic assembly company is required to conformal coat several
different circuit boards. In most cases we use urethane applied with a
brush and carefully avoid the locations the customer wants to not be
coated. Connectors, switches, sensors, test points, and mounting holes.
Other customers have specified the silicon based coating. Both coating
material is rather expensive. Much of it is ONLY available in metal one
gallon cans because bottles can't be shipped UPS. Urethane is available
in spray cans, but most cans are plugged up and won't spray, even right
from the distributor. Shelf life is almost zero. There is no return on
conformal coating material.
On Wed, 16 Nov 2011 22:32:33 -0700, Tony Hwang wrote:
Vertical orientation. The old board had rust running down from one
connection to the next, about five or six connections gone. It was in there
two years unused. Now I have freezing weather and can't wait for shipped
unit. If I have to replace it again it will cost double what I can find on
I would normally talk to company for possible fixes. Sometimes we have to
try to get the company to do a fix. They like a certain amount of repair in
Even if board is good, connectors will still have problems.
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