On 11/03/2015 06:26, Chuck Harris wrote:
Does KOH really evaporate, and spread in the wind?
I don't think it does.
In my experience, the damage done by nicad's is limited to
where the electrolyte dribbles, spatters, or wicks.
Powdered electrolyte can get all over things, but usually
it can be just brushed away, as it is not too corrosive
when dry.
If the switches are not covered with KOH dust and crust, I
truly doubt that they have any measurable amount of KOH
inside of them.
However,
If you want to be really sure, go to your grocery store and
buy yourself a gallon of steam distilled water for $0.50, or
so, and an empty spray bottle, like is used for window cleaner
and liberally hose out the switches and any other area you
are concerned about.
When you are done, shake, blow, or simply let drip as much
water as you can off of the unit. Set the unit up next to
a fan, and let the fan blow air on it for a couple of days.
It will dry out.
If you want to be doubly sure, a convection oven is the
answer. There are several ways you can get one on the cheap.
If your house has an electric convection oven in the kitchen,
you can use that set to 150F (50-60C). Or, you can put a
muffin fan on a simple stand, and put it in an electric oven,
with the door closed, and the oven light turned on. (Gas
ovens are fine too, if they do not have a pilot light.)
And, if you want to stay away from the kitchen, you can fashion
a simple convection oven using a cardboard box, a 40W lamp,
and a small muffin fan. Make sure the box is big enough so
that the lamp is no closer than 12 inches from any side of the
box, and make sure that the fan and lamp cannot fall over, or
the box move and cause issues... don't want to make a fire
hazard.
-Chuck Harris
Stan Katz wrote:
Now that I've restored my HP419A to running order for the meantime, I
have
nagging questions regarding the continuous use of the attenuator switch.
The main board of the instrument, A4, was badly polluted with an
invisible
layer of potassium hydroxide from the 30 years of being in the same box
with dead/mummified nicad batteries.
In accordance with
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC43-206part2.pdf
I
prepared a 3% boric acid solution and flushed the affected circuit board
several times, while scrubbing with a soft nylon toothbrush. I then
flushed
the board with hot water. After leaving the board on my furnace
plenum for
a few days to thoroughly dry out, the board problem was sorted out.
If the
KOH deposited an invisible layer on A4, then certainly, there must be a
layer of KOH on the attenuator switch's gold contacts, as well. I
posted my
concern about the KOH on a premier chemistry forum. The administrator
himself answered my query. He indicated that the only way to remove
the KOH
from the switch is to thoroughly flush with di water. There's no
place for
a flushing stream of water to exit the instrument safely. I'm not
about
to remove the switch! Now, I don't know the hardness of KOH, but
Potassium
has a very small .5 mohs of hardness. I presume, that KOH is similar. In
any event, I would tend to believe there will be some small abrasive
wear
from the KOH. The attenuator on a null meter is heavily utilized, and
even
a light abrasive can cause trouble eventually. Proper gold plating,
that's
kept clean, never suffers from abrasive wear. Improper plating, can
suffer
from adhesive wear, but I have confidence that the HP of the
1960s-80s was
using the finest gold plating available. I thought about applying
one the
the Deoxit products. A careful reading of the Deoxit literature
claims that
the D-series treatment is for non-critical metal surfaces. I think
that
the gold plating in the HP419A qualifies as quite critical. The
Deoxit G
series literature leads me to believe it may not have enough cleaning
action to flush out the KOH. Also, please note, only the removal of
oxides
is mentioned as a feature of the Deoxit line. What other corrosion
products
that may be removed are not mentioned.
A proper science project would be to obtain Bromothymol blue indicator
solution, and prepare it with Phosphoric acid in accordance with the
above
citation. I could then apply it to the switch contacts ( in itself a
PITA
job ), and then try the Deoxit G series, and perhaps other brands of
contact cleaner to see if the KOH is truly removed without resorting to
water. I'm actually willing to take on such a project ( it's a hobby,
after
all ), but I don't even know how to procure a proper concentration of
Bromothymol blue from over the internet. Without access to purchase
orders
through a university, or corporation, even innocuous chemicals are
unobtainable from US chemical supply houses directly by individuals.
There
are lots of offers on Ebay, but I have no way of knowing if what's
sold is
a the proper concentration. I don't even know how to specify what that
concentration should be.
Yes, I should get on with
