Re: [volt-nuts] OCD About My HP419A Attenuator Switch Gold Plated Contacts
Yes, you are being a little too OCD about this. Instrument washing issues come up often, and there are plenty of opinions available - here are some of mine: In the 419s that I have, the battery leakage crud has not gone beyond the circuit boards or maybe the edge connectors. Cleaning the boards should take care of it, and it's not that complicated. For stubborn alkaline deposits, a vinegar wash (if necessary) should neutralize and descale, followed by scrubbing with liquid dish detergent and a toothbrush, and then lots of rinsing with hot tap water and finally thorough drying - preferably with an oven, but air drying for a couple of days should suffice. Blasting with compressed air helps to get most of the water out. Don't bother with pH indicators - I doubt they would show much unless there's so much crud that you can see it anyway. If KOH has gotten onto any critical circuits, it could cause symptoms such as excessive leakage currents, since it's hygroscopic and would tend to be ionized and conductive on the surfaces. If you are concerned about the switches, you can wash the whole thing with tap water and liquid detergent. First, remove or protect the meter movement and any batteries, and maybe the pilot light. As I recall, the rest is pretty much open so easy to flush out. There are different schools of thought about items such as power transformers and pots - you have to apply judgement on whether they will wash out and dry OK. If in doubt, protect them from the washing process. When washing electronics, always finish with an alkaline (like liquid detergent) to neutral (water or alcohol) step before rinsing - you don't want any acidic residue left anywhere. Lots of rinsing and thorough drying is always good - several days of air drying for a whole instrument. You may have to relube some of the switches - I don't recall if they have grease on the contacts or mechanisms. Ed ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] OCD About My HP419A Attenuator Switch Gold Plated Contacts
Potassium Hydroxide absorbs carbon dioxide from the air quite rapidly, so what you find on a circuit board is much more insoluble potassium carbonate and/or bicarbonate. Being an ionic compound you may well find copper carbonate, zinc carbonate, tin carbonate and lead carbonate from other metals on the board that have been dissolved. So judicious use of a weak acid, like acetic acid, may be necessary to dissolve these deposits. After that plenty of demineralised water and a long drying period in front of a fan. cheers, Neville Michie ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] OCD About My HP419A Attenuator Switch Gold Plated Contacts
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
[volt-nuts] OCD About My HP419A Attenuator Switch Gold Plated Contacts
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 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 ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.