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Thread: Deep Submergence Scanner Amps.

  1. #1
    mixedgas's Avatar
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    Default Deep Submergence Scanner Amps.

    This is the results of something I did a few months ago. While I'm waiting on the replacement galvos, I thought I'd write this up. Its interesting. Crazy, probably useless, but interesting...

    I was asked to try to recover a few salt soaked classic circuit boards. These were submerged in Atlantic waters during Hurricane Sandy. I of course told the owner they are probably useless and will never be 100% reliable.


    Submerged Electrolytic capacitors, dip switches, most tin plated connectors, and 10 turn potentiometers will need replaced, period. Surface mount chips trap salt underneath, and may just be a writeoff.

    Step One, Making the solutions.

    Citric and Boric Acids are pretty much harmless, unless your a fish, insect, or reptile.
    Wear rubber, latex, or nitrile gloves and eye protection when doing this.

    In a two litre pop bottle, saturate two litres of hot water with drug store Boric Acid. Add two tablespoons of Sodium Chloride, aka table salt. Iodized salt is fine.

    Make the dilute working solution. This is done by adding 1/4 litre of this master solution to a new 2 litre bottle and filling the bottle with hot tap water.


    In a two litre pop bottle, saturate two litres of hot water with grocery store Citric Acid. Add two tablespoons of Sodium Chloride, aka table salt. Iodized salt is fine. Make the dilute working solution. This is done by adding 1/4 litre of this master solution to a new 2 litre bottle and filling the bottle with hot tap water.

    While strong, saturated working solutions might seem ideal, they leave no place for the salt on the board to dissolve. So you need dilute solutions.....

    Step one: Flush board to be cleaned with warn fresh water in a bowl with a drop of dish washing detergent. The detergent acts as a surfactant and loosens up the salt and organic crud for the next step. Do not scrub the board with just fresh water. Soak the board a few minutes. Add a pinch of table salt and allow to set a few minutes. Leave the board wet.

    Step two: In a small plastic bowl, submerge the board in the hot, dilute, Boric acid solution.
    Let it set for five minutes or until the solution cools enough that you can get your gloved fingers into the bowl with the board. Scrub gently with a old soft bristle tooth brush that you will dispose of when done. Keep the board wet.

    Step three, add several ounces of rubbing alcohol or methyl alcohol to the bowl. This will neutralize the acid by forming a harmless organic compound, a borate. Let the board set a few minutes in the alcohol. Scrub a bit more with the used toothbrush. Pull the board out and flush the board with more alcohol.

    Step Four. Submerge the board in the warm citric acid solution. Allow to soak a few minutes. Scrub with used toothbrush. Add alcohol to the board as before and let set.. Flush board with fresh alcohol as before.

    Step five. Drying. Submerge or flush the board in alcohol. Remove board and blow fluids off with air if possible. Do not bake or blow dry board. Set board on its side so it will drain, on paper towels.

    Step six, dispose of the toothbrush. You don't know where it has been, anyways... Recycle the pop bottles...

    If you have a spray can of circuit board cleaner/flux remover now is the time to use it.

    Replace electrolytic caps, remelt solder joints with RMA flux as needed, replace potentiometers, replace connectors. Expect to have to troubleshoot a few problems. Expect microprocessors or surface mount chips to need replacement.

    Do not expect a miracle. This technique turned a pair of scanner amps into a pair of inexpensive backup scanner amps. It saved some custom boards that are 20 years old.It works with "through hole" old style circuit boards. It may not help you with surface mount gear. These boards had solder masks and plated traces. They survived. Exposed copper will NOT survive.

    This will remove the plasticizer from the outer layer of the board. The board will never look "Glassy" or clean ever again. All solder that is not remelted will be a dull grey. But it did work.

    Can you trust gear recovered this way, no.... Is it fun, yes. Did two scanner amps work when I was done, yes. The jury is still out on the CADAMOD boards. The upper half, which is the Pangolin custom part, are salvageable. The lower CADA part, made by Alesis, is gone.... The ALE supply, which was exposed to just salt fog and humidity will probably live.

    Thanks to my friend who does salt water aquariums for the tip on the weak acids...

    Steve
    Last edited by mixedgas; 09-24-2014 at 09:07.
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  2. #2
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    Steve,

    Thanks for the very interesting write up!

    I once "saved" a few Carver PT-2400 PA amplifiers that got wet during a July downpour in the summer of 2004 that overwhelmed the pumping capacity of downtown New Orleans. But they were only submerged for about 2 hours before I got to flush them clean with distilled water. I then dried them with fans and electric heaters. Next I placed them in direct July sunlight for about 5 hours each day for about a week. They worked fine but I did have to change the gain potentiometers about 2 months later, but no other problems popped up. Of course, this was only rainwater along with whatever dirt & funk washed up from the street an into the building they were in, rather than the salt water from Sandy. They were still working one year later when they were finally killed.

    After Hurricane Katrina, I was not as lucky. I had some LCD projectors, club lighting, an EAW sound system with the same Carver amps, plus a bunch of misc related gear stored in a rental house in New Orleans about 2 miles from the 17th Street Canal breach that was shown constantly on TV. The gear was underwater for about a month! The water was brackish water from Lake Pontchartrain plus mud, gasoline, oil, antifreeze, paint, pesticides and who knows what else.

    When I opened the amps, they were rusty and full of mud. I washed out an LCD projector and then as I gently brushed the PCB with a soft paint brush, the SMD capacitors like this Click image for larger version. 

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ID:	44885 just fell off. It was as if the water/funk combo just dissolved the solder.

    The only thing I was able to partially save were the EAWs. The crossovers cleaned up no problems. The compression drivers cleaned up after removing the diaphragms from the drivers and cleaning the magnet gap. Even the fiber fill insulation cleaned up in the washing machine. The cabinets are made from exterior grade Baltic birch wood and sprayed inside & out with some kind of urethane or something similar. The cabinets did not de-laminate or swell up in any way. I just washed them good. The 15s needed to be re-coned and the 7" mids were all replaced with new ones.

    All in all not very successful. To re-cone an RCF 15" woofer is more expensive than the cost to buy many new, lower performance woofers. Six LA325 boxes times 2 15s in each, means 12 re-cone kits at about $200 each. The 12 7" mids are not cheap either, and the the 4 double 18 EAW subs needed to be re-coned too.

    I'm sure more could have been saved if the water had been pumped down faster. Hopefully I'll never have the need to try your method, but it looks like the way to go if I do.
    Eric in New Orleans

  3. #3
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    ultrasonic bath in Freon might do the same job. the surface oxidation really doesn't matter
    could also flux the whole thing and reflow it.

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