Playing with HP2640B

[Henk Gooijen]

Van: Mattis Lind via cctalk<mailto:cctalk at classiccmp.org>
Verzonden: vrijdag 17 november 2017 11:52
Aan: David Collins<mailto:davidkcollins2 at gmail.com>; General Discussion: On-Topic and Off-Topic Posts<mailto:cctalk at classiccmp.org>
Onderwerp: Re: Playing with HP2640B

The screen on my HP2640 had degenerated quite far. It was only a spot in
the middle, 2 by 4 inch, that still attached the glass to the CRT. I used a
thin fish fillet knife to dig through the remaining glue.

Before

https://scontent-arn2-1.xx.fbcdn.net/v/t1.0-9/23622163_10155696765784985_6518064439030378363_n.jpg?oh=44cbf7f7f00d6e25155c208124e20a38&oe=5AA7349D

The result after:

https://scontent-arn2-1.xx.fbcdn.net/v/t1.0-9/23621971_10155696757184985_1959733265676657917_n.jpg?oh=36a20689c0fb5a16de7fc4df138a40e0&oe=5A9993B1


Anyhow, I researched the glue a bit. The glue is, as far as I understand,
PVAc (PolyVinylAcetate, sometimes also known as PVA). PVAc is not soluble
in water. It takes quite high temperature to melt it. However PVAc is
soluble in many esters. I bought some Butylacetate. It dissolves sample
bits of glue from HP2640 quite well and rapidly. Butylacetate has quite
high boiling temperature (about 120 degrees centigrade) and thus does not
evaporate that quickly. So my idea is now to test on a 2645 screen or VR201
screen by adding some butylacetate and seal with some thin plastic wrap
foil and let it dissolve a bit. Then use the fish fillet knife again and
repeat the process.

/Mattis


Wow!  Excellent job Mattis  <thumb up>
I have seen that HP2640 when it still was in bad shape. The HP2640,
that I have, has many tiny spots on the screen. Your “result after”
really looks fantastic.
What’s not clear to me, after removing the old “protection” sheet, did
you apply some new “protection” sheet, or leave the tube “as-is” ?
I doubt whether that “protection” sheet would really help much if
the tube would implode (for whatever miraculous reason) …

Henk