Nicely done. I restore and 'upgrade' NES consoles as a hobby. Most of these steps feature good restoration techniques. However, for anyone here looking to do the same, please skip the polyurethane step. While it may impede corrosion, that step makes the system much harder to repair/modify in the future.
Is there — as Julian Baumgartner would say — an “archival-grade reversible isolation-layer varnish” that could be applied in place of poly sealant? Silicone, maybe?
Would shellac work or traditional lacquer[0] work? They both cure by drying, not polymerizing, and can be removed decades later with the original solvent: alcohol in the case of shellac, or lacquer thinner in the case of lacquer.
I haven't had any experience with lacquer because traditional lacquers almost have to be sprayed, which I am not equipped to do. I have plenty of experience with shellac because you can brush it and get a pretty decent finish off the brush, or French polish for a more refined finish. French polishing takes advantage of the aforementioned properties of shellac: besides laying another thin layer down, you're also redisolving the existing layers and smoothing them as you go.
Traditional varnishes cure by polymerization, and generally cannot be removed with mineral spirits. That isn't to say you won't ruin the finish trying, but you'll need a different solvent if you want it gone cleanly.
[0] lacquer has become an almost meaningless term. There are products that might or might not technically be lacquer that are called lacquer or water borne lacquer or some other phrase that includes the word. I'm referring to the stuff that uses lacquer thinner for the solvent. You'll know it if you smell it: it smells like it's giving you cancer right now, not in 30 years.
Mind you, in this case, we're talking about something that 1. doesn't have to dry clear (and in fact can dry entirely opaque), and where 2. it'd be much better if you could remove it by peeling it up, rather than by using a solvent, because many of the components have plastic housings that don't take kindly to, well, any strong solvent really. The goal isn't an art piece — it's to create a barrier to moisture/corrosion for a board within an unlit box. If you want to do a repair, you'd entirely remove this layer before doing it; and entirely reapply it afterward.
Any general purpose conformal coating is fine. I don't understand why it'd make repair more difficult. Most of them can be soldered through directly, or you can use thinners or strippers to remove them.
I'm curious why the conformal coating was added to the bottom of the PCB, it didn't seem at all corroded after 30 years. On the other hand, I'm surprised they didn't replace all the electrolytic capacitors in the A/V area -- or even the whole unit. If some of those leaked already, IMO, the rest will leak soon too. Seems a bigger risk than a lack of conformal coating. shrug
Either way, excellent video and very well put together. I love seeing stuff like this.
