Jack Erbes wrote:
Len wrote:
Any thoughts on why a Uniden QT206 digital depth display fogs up to
the point of being unreadable? Has anyone else experienced this?
snip

The case has to be vented to allow for expansion when everything warms
up. As it cools down, it pulls moisture laden air into the case and
that condenses inside the unit. Next warm up cycle, the air expands,
then the moisture is warmed up and condenses on the glass and
components. But there is not enough air movement to push the moisture
out so from that point on, the moisture is there to stay, it just cycles
back and forth and the amount can slowly increase inside the unit.

Some marine units used to be sealed and nitrogen filled and that worked
okay for a year or two but it was really impractical to maintain the
seal with controls, card slots, etc.

Some models used things like small silica gel ("Do Not Eat") packs
inside and the moisture would collect in those. I'm not sure it was
much help because they could warm up and could cook the moisture out of
the silica gel.

The only real cure is to open the case and drive all the air and
moisture out with warm (not hot) dry air. Several hours with a gentle
warm plow from a hair dryer or heat gun will do it. Do it at home or in
the shop, cool it slowly and close it back up in a dry place.

This can't be an entirely isolated incident. Has anyone had success
sealing a gauge from the back (this one sticks into the galley
cabinet) to defeat what appears to be a design deficiency?

That sounds like a dry but open to the atmosphere location. You might
try putting a loose fitting bag around the back of the instrument. Snip
a corner off to run the leads in, use rigging tape to seal the bag to
the housing. That small amount of dead air space may buffer the heating
and cooling cycles enough to prevent or at least slow the moisture
buildup.

If the font of the instrument is not well sealed and/or the instrument
is not mounted on a thin bead of silicone, the moisture may be getting
in from the front. There is not much hope for curing the problem with a
poorly sealed housing.

Jack.




Thanks,
Leonard
s/v "Meeresstille"



Jack,
The JRC radar display has two GoreTex patches over breather holes which
keep out liquid water but I am sure permit passage of water vapor laden
air. I only mount the display on the binnacle if I anticipate needing radar.
Dick
Nonsuch 26, Swoose