Removing PVA from a CRT

[ED SHARPE]

Saving this  thread!
Thanks  for the great info and hints  as we have a stack of HP  254x terminals  and some of them  graphics  hi end  ones... have  no idea if they  will light off for  not but thankful to have  even as  static  displays. 


Ed Sharpe  Archivist for  SMECC  
 
 
 
 
 
In a message dated 11/25/2018 12:27:56 PM US Mountain Standard Time, cctalk at classiccmp.org writes:

 
>

> The heat pads are worth a shot if they can maintain temp long enough to do
> the job, though you'll be up against quite a bit of thermal mass with that
> thick glass. The old trick that people are still using today with vintage
> 21" CRT's is to put them in a kiddie pool outside and let the sun warm the
> water. You don't want to start too hot for risk of cracking the glass.
> *Glances out window* I can tell you that trick wouldn't work here today,
> nor for 6 more months.
>
> If you have a way of ensuring the optically clear adhesive sheet bonds
> evenly and won't yellow, I don't see why that wouldn't work. I recall
> someone did do the foam tape/packing tape operation and then DID fill the
> void with a PVA type liquid material. Risky to ensure all the air bubbles
> made their way out, for sure. -C
>
>
>

I did some tiny bit of research into this when I dealt with my HP2640 B and
a VR201. The former was in a condition where just a tiny fraction in the
middle of the screen attached to the glass so it almost fell of by itself.
With the VR201 the story was a bit different. I didn't want to heat it up
like most people seems to be doing when looking at the Youtube clips. I
checked the solubility of the PVA (PVAc really, PVA is something different)
in water and nothing happened at all. I tried to heat the water a bit but
no change. I am not sure how come people are successful with this method.
But I investigated PVAc a bit and found out that it is soluble in various
esters. I bought a bottle of Butylacetate and indeed it made it dissolve
quite well. Butylacetate is mostly used as as solvent for polyester paints,
and I think it is an ingredient in what women use for removing nail polish
(when not using acetone). BTW Acetone is also dissolving PVAc very well but
the boiling temperature is much lower. As far as I can understand
Butylacetate is not very harmful to deal with either.

What I did wash to inject butylacetate using a long needle syringe in
between the front glass and the CRT and let it rest for a few days. I put
some plastic wrap around to contain the butylacetate a bit more and then I
repeated it a couple of times until the front glass simply fell off.

This is the method I will use in future with my other screens that have the
same problem (HP2645, HP9835, HP9845, (Possibly also the Tektronix 4016
depending on the type of front glass used).

/Mattis