[volt-nuts] OCD About My HP419A Attenuator Switch Gold Plated Contacts

M K m1k3k1 at hotmail.com
Wed Mar 11 03:03:06 EDT 2015

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 
>> 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 my life, but I've invested quite a few hours
>> restoring this instrument, and I just can't let this situation fester
>> without a resolution.  Can anyone on the list help put me out of my 
>> misery?
>> Stan
>> _______________________________________________
I would have thought that KOH would turn into K2CO3 over time, and that 
would not be quite so agressive to deal with

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