How to remove rust from EMF shield

[arroz]

Hi!

Restoration of an LC III is going great, board recapped is working perfectly! Now, the top shield is in a sad state (see photo). What's the best way to clean this? Assuming I separate the shield from the case, would a vinegar bath for a few hours work? What techniques do you use?

The video and SCSI ports are also quite rusty. What do you recommend for those?

Thanks,

Miguel Arroz

 

[finkmac]

evaporust will get the corrosion off, but will also strip the coating... meaning it'll oxidize again. a clear or zinc coat will prevent that.

 

[Phipli]

I use a wire brush on a Dremel or an angle grinder depending on how bad it is, then paint it with electrically conductive paint if you're behaving, or just zinc primer if you just want to preserve it.

 

[Phipli]

It doesn't look too bad to be honest. The main issue is that it is hard to do the other side without removing it, and removing it is generally a destructive process (they melt the plastic to hold it in place).

 

[Callan]

This process depends on how nice you want the restoration to be. Easy way is to just cut the melted tabs with.a razor blade, then you can use the above methods to remove the rust. Add a fine sandpaper to that list as another (once removed - hard to do while attached to the case). You can then just attache the shield back with a hot glue gun.
Another method to remove the shielding is to use hot air on the plastic tabs and pull up on the shielding as you heat the tabs. This will pop the shielding from the tab. If done right you can trim the plastic tabs so they will fit the shielding easily when your putting it back on. . You can then re-melt the tabs to secure the shielding. if you have access to a small sand blasting setup you can use that to strip the rust too.
When done, like everyone has pointed out, you'll need to paint, coat with a sealent, or even powderxoating works. It just depends on how nice a finished product you want. There are some good metallic paints out there that also make it look like the original.

 

[s_pupp]

A soak in Evaporust followed by a wipe of CorrosionX has restored rust-crusted junk floppy drives to good working order, with no return of rust yet, aftee more than a year.

Naval jelly would get rid of rust and leave a cosmetically unfavorable but very effective black antirust coating of the rusted areas.

 

[arroz]

Hi!

Thank you for all your answers! All of this should point me in the right direction.

I don't think I can avoid separating the shield from the case. To re-attach it, I'm considering borrowing an idea from modern Apple and use magnets. Glue magnets to the case, and attach the shield magnetically. However… I was just testing that theory. I have 3 machines here: one LC 3 (upper shield rusty, the one in the photo, lower shield is fine), one 475 with both shield rusty, and one 475 with no rust. I tried a magnet, and:

• LC 3, only the upper shield is ferromagnetic (the magnet attaches to it, but wont attach to the lower shield).
• Non-rusty 475: same.
• Rusty 475, both upper and lower shield are ferromagnetic.

So… I have no idea what's going on here. Different materials? The only constant seems to be the all rusty shields are attracted by the magnet, but not all the shields it attaches to are rusty (yet?). It's not even "LC 3 is different than the 475s". One of the 475 has the same behaviour as the 3, the other 475 is different.

Also, how to handle the ports? The LC 3 has the SCSI and video ports with the outer shield rusty. One of the LC 475 has the entire box of the audio in jack rusty. I assume dipping the board, or even just the ports, in Evaporust is not the best idea.

Thank you,

Miguel Arroz

 

[s_pupp]

I was researching the use of Evaporust on circuit boards last year, given a fair amount of rust stains on the bottom of a Mac SE logic board, and found info (sadly I don't recall where) that solder joints can be weakened by Evaporust. I can't say what that reaction would be.

There are some grades of stainless steel that are not drawn to magnets; that fits with a non-rusty non-magnetic shield in an LC475.