hello !
I recently got two old AT cases (286/386 period) that share the same feature : they both have what looks like a rough paint at the back of their front panel (including the drives bay covers).
Anyone knows what it is, and what is the utility of that ?
And (maybe paranoid question) is that somehow dangerous ?
Thanks !
I need a vacation.
I bet it is some kind of conductive paint to create some kind of Faraday cage... Can anyone confirm?
kwyjibo wrote on 2020-05-17, 10:15:I bet it is some kind of conductive paint to create some kind of Faraday cage... Can anyone confirm?
That would be my first thought as well, specifically to block RF. I know on the old Macintoshes (the 128k/512k/Plus/SE/etc. types), they are internally painted with a silver-color paint that is said to have RF blocking properties. They often still use an RF shield around the motherboard, but I figure the paint is enough for any RF from the analog board/power supply circuitry.
kwyjibo wrote on 2020-05-17, 10:15:I bet it is some kind of conductive paint to create some kind of Faraday cage... Can anyone confirm?
No, as it would not work in these two examples. For shielding, conductivity must not only be quite high (nothing a thin layer of paint could do), it also needs connection to all other parts of the shielding and to ground.
That's simply bromide or some other stuff to make the plastic more resistant to heat/fire.
OK thank you.
That sounds toxic ... is it ?
I need a vacation.
No, it's not toxic. At least not to the touch. And I doubt you are going to eat it. 😉
derSammler wrote on 2020-05-17, 12:29:No, it's not toxic. At least not to the touch. And I doubt you are going to eat it. 😉
OK good, thanks.
I need a vacation.
Using conductive paint for easy shielding of plastic cases is a common thing. It has been used excessively on 80s and 90s PCs with varying suitability. I think this is a conductive coating of graphite (grey color) and copper (copper color ^^ ).
Check for yourself with a multimeter wether the paint is conductive. You may have to increase the surface contact of your probes with some crumpled tinfoil or something.
Flame retardants are most likely included in the plastic mix.
It's anti-flame coating. First one most likely carbon-based, second one is bromide-based. Believe it or not.
It's completely silly (sorry) to even think this is for shielding. That part is mounted in front of a steel case which is already heavily shielded by itself. Yes, there were a few computers using paint for basic shielding. But these had plastic cases where this made sense. It was in no way common. Most coatings had other purposes.
I already said it had been used excessively on 80s and 90s PCs with varying suitability. Often it was applied simply because some country's regulations required it.
Also that graphite layer looks mighty thin (See the scratches on the grey paint? We're talking micrometer layers.) to be an anti-flame coating while at the same time a very thin layer of conductive paint is usually what is used in shileding.
So I'm having a hard time following your reasoning.
The paint is indeed conductive (and well conductive, I did not need to extend the probes of the multimeter). Tested on the two panels with the same result.
I need a vacation.
Grey or red paint are EMI paint, can be also smooth grey silvery look. I seen that in PS/2 and some other clones.
Cheers,
Great Northern aka Canada.
