[vcf-midatlantic] Museum report: terminals (Ethan Dicks)

[Michael Thompson]

> From: Ethan Dicks <ethan.dicks at gmail.com>
> Subject: Re: [vcf-midatlantic] Museum report: terminals
> On Mon, Jul 9, 2018 at 12:27 PM, Jonathan Gevaryahu via
> vcf-midatlantic <vcf-midatlantic at lists.vcfed.org> wrote:
> > On 7/9/2018 11:39 AM, Herb Johnson via vcf-midatlantic wrote:
> >>
> >> I saw many "moldy" CRT's - that's when the front of the CRT has a
> >> transparent cover that's separating from the glass. Repair means
> replacing
> >> the CRT, which can take most of an hour depending.
>
> AFAIK, it's bubbles in the PVA layer between the face of the CRT and
> the implosion protection screen.
>
> > These CRT tubes don't have to be replaced, the CRTs can be very carefully
> > heatgunned to remove the front protective glass cover and scrape out the
> > 'cataract' goo. I think Ian has done it to a few of them already?
>
> I've done it with a VT220.  You can use a heat gun or a hot wire to
> cut the PVA to free the shield from the tube, then it's all cleanup.
> You do need to re-install the shield because otherwise the CRT clamps
> don't fit really well and the tube slides around.  I used dots of a
> thick (1mm?) silicone "tape" on the corners and it worked well.  Just
> a small airgap in front of the face of the tube instead of a layer of
> what is supposed to be optically clear PVA.
>
> -ethan
>

We had a VT14 at the RICM that had cataracts. We used dental picks to
remove the silicone holding the metal mounting band to the CRT. We planned
on using a hot wire to cut the PVA, but when we started picking at the
edges of the PVA we found that very little PVA was adhered to both the CRT
and the shield. Cleaning up the PVA was tedious, but not difficult.

We were concerned about putting a CRT without the PVA in a public place in
the museum. We had images of a young visitor breaking the CRT and glass
flying everywhere.

We bought some 0.093" thick Lexan at Home Depot, waited for my wife to go
shopping, and put the Lexan on top of the glass shield in the oven. When
the temperature hit 325F the Lexan conformed to the glass shield. We
trimmed the Lexan to the same size as the glass shield, and use silicone to
hold everything together. This is probably a lot safer than the original
PVA and won't degrade.

There are pictures and a description of what we did here:
http://www.ricomputermuseum.org/Home/equipment/dec-pdp-12/dec-pdp-12-restoration

-- 
Michael Thompson