I am working on a piece of vintage

[Longfellowe]

I am working on a piece of vintage audio equipment from McIntosh that has damage to the chrome plated chassis from a leaking electrolytic capacitor.

The new capacitor will cover the damage cosmetically but I need to treat the chassis itself to prevent additional problems from rust and loss of more chrome going forward.

I’m good with the electronic part of this repair but my knowledge of metallurgy is abysmal. Any help and suggestions on a treatment/sealing regime would be greatly appreciated.

 

[TugboatEng]

A little silicone grease may be all you need. It provides good corrosion protection and the capacitor will protect it from getting wiped off. It's non-conductive so there is no risk or it messing with any of your electronics.

 

[Compositepro]

https://www.google.com/search?client=firefox-b-1-d&q=electoplating+pen

 

[Longfellowe]

Tugboat: Thanks for your response. The silicone grease idea is certainly simple and one I had not considered. I'm guessing it would be a good idea to remove all the visible rust before putting it on? There's not much, but anywhere there was chrome there is now a bit of rust on the naked steel.

Compositpro: This is very interesting, I had never heard of an Electroplating Pen before. But, of course, that's why I came to this forum for help from you guys, to learn new things and ideas. Thanks for posting.

 

[EdStainless]

I would start by scouring the area with a baking soda slurry.
Get clean metal and neutralize any acid residue.
Then after a good drying use the silicone grease.
You could re-plate the area with electroless Ni as another option.

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P.E. Metallurgy, consulting work welcomed

 

[Longfellowe]

EdStainless: Another interesting idea! I understand the baking soda slurry to clean and neutralize acids but the electroless NI plating is a new one. I did some quick on-line research and it looks interesting but every example I saw showed the object to be plated immersed in a chemical bath. This is not really practical in my application since it would require stripping the chassis of all components, a difficult job and fraught with unknowns on a 50yr old piece of gear. Is electroless NI plating a process that can be "painted on" and then cleaned off when its work is done?

 

[EdStainless]

With most plating on steel you start with a Cu flash, a very thin Cu plate.
This is autocatalytic (electroless).
You can buy a paste that you rub on and then wipe off leaving a thin layer of Cu.
I have seen ENi done with a brush.
The electroplating pen with Cr works well also.
Any of the localized methods will tend to leave an uneven looking finish.
Your other option is Rustoleum

https://www.rustoleum.com/product-catalog/consumer-brands/imagine-craft-and-hobby/metallic

https://www.rustoleum.com/product-catalog/consumer-brands/auto/specialty-paints/metallic

Paint may be the easier route, and from a distance it will look fine.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Longfellowe]

Thanks, EdStainless. Cosmetics are not my top concern because the new capacitor will hide anything I do to the surface now. I'm most concerned about stopping the rust or other corrosion dead in its tracks so that, in the future, it doesn't continue to eat its way under the chrome and show up outside the new capacitor's footprint. I think I need to do some more research on the electroplating pen idea.

 

[TugboatEng]

Chrome plating has fractures and pores in it's surface so it's a poor method of corrosion protection. That's why copper or nickel are used to coat the part prior to chrome plating.

Your application as described is trivial. Any solution is likely going to work well. I suggest going with the simplest solution. A tube of dielectric grease is available down the street at your local auto parts store. If you want to go above and beyond follow Ed's advice about cleaning first. You could also use a silicone sealant. Dow Corning 734 is flowable and works great for encapsulating things.

 

[Longfellowe]

TugboatEng: You're absolutely right, simple is better. But when you're a noob, like me, it's reassuring to have options and to learn as much as you reasonably can so when you finally make a decision you feel it was an informed one. Thanks to all for sharing your expertise with me on this project.

 

Don't forget to address damage done to the underside, you want to seal the entire area to prevent creeping corrosion. I expect it should be easily accessible without further disassembly.

Seems strange to chrome plate a sheet metal part when making it from brushed stainless steel seems simpler and cheaper.

Thanks folks for some useful DIY suggestions for the day I inevitably face a similar problem.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[TugboatEng]

Don't forget that this is "vintage" and stainless steels may not have been in widespread use.

 

[Longfellowe]

I believe the chrome plating was a cosmetic issue. Many older MAC power amps did not have the fancy front panels that contributed so effectively to the WAF (Wife Acceptance Factor) of their equipment, chrome was a way to add "sparkle". Plus these products were originally designed in the 50's-60'S when lots of chrome was a big deal, especially on cars.

The current generation of MAC products do indeed use polished stainless in place of the traditional chrome.

 

[EdStainless]

I had a pair of old 60W mono MACs, no panel, no controls, just amplification.
We ended up using them in the lab because you could use them at high frequency since there was no output filtering.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed