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geekhack Community => Keyboards => Topic started by: Bucake on Sun, 04 October 2015, 16:23:09

Title: Plastic sheet..?
Post by: Bucake on Sun, 04 October 2015, 16:23:09

welcome!


so i've opened up an old zenith keyboard (i think the model is 100-1886).
the pictures below show the bottom and top of the case detached.
the bottom part is metal, and attached to it is a plastic sheet in the shape of the PCB that's positioned above it.
so.. i presume the purpose of this plastic sheet is to prevent the bottom(metal) of the case from messing with the PCB(??)

and then my 'real question' is; what exactly do i need to buy to replace this sheet with?
because i have already removed that plastic sheet, but its condition isn't so great anymore and therefore i'd rather install a fresh one.. :)

pictures:

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(http://i.imgur.com/qBVYopp.jpg)

(http://i.imgur.com/clEA0dV.jpg)

(http://i.imgur.com/kgmMHQz.jpg)

(http://i.imgur.com/BXb8aVR.jpg)

why removed it at all?
the pictures don't show it well, but there are a bunch of small rust spots under the sheet.
it was also virtually impossible to remove all the dirt and dust that was under the sheet (without removing it).

oh, and what would you guys use/recommend to get rid of small rust spots..? just anything acidic, or am i better off getting something 'proper'?

Title: Re: Plastic sheet..?
Post by: ika on Sun, 04 October 2015, 16:27:00

Anything that insulates is fine. Vinyl sheet, contact paper, wire shelf liner (the kind without holes) etc. As long as it's thick/durable enough to prevent anything from the PCB shorting on the metal case.


As for the rust, if your metal is made of steel, you can use a mild acid (lemon juice, vinegar) or oxalic acid (barkeeper's friend) diluted in water, a cloth, and some elbow grease to buff it out.

Title: Re: Plastic sheet..?
Post by: fohat.digs on Sun, 04 October 2015, 16:37:06

I always look to Mylar as my first solution for that sort of thing. But I have several sheets of very thick high quality stuff that was "drafting film" back in the 1980s when high-end plans were drawn in ink on mylar, just before CAD came along.

Title: Re: Plastic sheet..?
Post by: Oobly on Mon, 05 October 2015, 01:44:43

Any thick enough insulating material should do the job, but you may have difficulty finding something that will work just as well as the original. Why not just put the original back in again, it's inside the case, so it's not going to be visible.

If you can get something with phosphoric acid in (Ospho?, Deoxidine?), that's about the best for rust on steel. It converts the iron oxide to iron phosphate and creates a stable barrier layer. You brush on just as much as needed.

Another technique, which is perfect for removing rust from chrome and may work on your small spots is Coke and aluminium foil. Coke contains phosphoric acid and in combination with the alumium it abrades the soft surface rust away and gently converts the remaining surface layer.

Title: Re: Plastic sheet..?
Post by: Bucake on Mon, 05 October 2015, 08:22:38

thanks a lot for the replies :)
everything's noted!


went ahead and used lemon juice and a toothbrush, but it sort of dissolved the top (coating?) of the metal:

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(http://i.imgur.com/5pgfdwF.jpg?1)

as you can see at the top left, it left the area a bit black-ish. the rest looks like it's sort of bleached and it feels smooth (while the center part feels textured. i guess that texture is some kind of coating).

i got Rust Oleum paint recommended to protect the metal (thanks fohat!).
can i just paint/spray the plate as-is, or does it need some kind of other treatment first?

Quote from: Oobly on Mon, 05 October 2015, 01:44:43

Any thick enough insulating material should do the job, but you may have difficulty finding something that will work just as well as the original. Why not just put the original back in again, it's inside the case, so it's not going to be visible.

yeah, my fear is that it won't work as well as the original.
but here's the thing:

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(http://i.imgur.com/ectb3yB.jpg?1)

even before pulling it off, it was full of 'cracks', and pulling it off gave it a bunch more. it also curled up like that because of the pulling.
on top of that, the double-sided tape that attached the plastic sheet to the metal is quite stuck. i probably could get it off, but i bet it would take 2+ hours to remove the tape and then remove all of that residue.
(feels like a waste of time because of the shape of the plastic..)

i found this place-mat, any idea if it would do the trick? :) it's some kind of translucent plastic. not sure what else to say because i am a total noob.

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(http://i.imgur.com/9Gc31fO.jpg)

oh, i also dumped a bunch of screws and springs in lemon juice for a few hours, but they look like i burned off the coating there as well:

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(http://i.imgur.com/V4w9n46.jpg)

can it hurt to just put them back into the board like this, or should i give them some protective layer/coating as well..?


sorry about that wall. this is pretty much my first 'restoration' project, and i'm just struggling :D

Title: Re: Plastic sheet..?
Post by: fohat.digs on Mon, 05 October 2015, 08:49:02

Quote from: Bucake on Mon, 05 October 2015, 08:22:38

can i just paint/spray the plate as-is, or does it need some kind of other treatment first?

yeah, my fear is that it won't work as well as the original.

the double-sided tape that attached the plastic sheet to the metal is quite stuck. i probably could get it off, but i bet it would take 2+ hours to remove the tape and then remove all of that residue.

i found this place-mat, any idea if it would do the trick?

oh, i also dumped a bunch of screws and springs in lemon juice for a few hours, but they look like i burned off the coating there as well:

can it hurt to just put them back into the board like this, or should i give them some protective layer/coating as well..?

Primer is usually good ("auto" primer is usually rust-preventive) but if the surface is clean the paint with primer included is probably good - the keyboard will have a pretty comfortable environment if you avoid spilling liquid into it.

Adhesives usually come up pretty well with naptha (old-fashioned cigarette lighter fluid) but it is hard on paint and plastics so work quickly and clean the area thoroughly as soon as you finish.

A placemat should work well, as would a silicone baking sheet, if the thickness is not too great.

I always wash incidental metal parts with something like Dawn dish soap and a light sponge or brush (or alcohol if necessary), then quickly dry them and wipe them down with oil (in the US the stand-by is called "3-in-1 Oil" found on every workbench). After coating the surface I wipe them with a dry paper towel to get 99% of it back off.