Very interesting! Thanks - comments below.
--- Dave Brown <tractorb_at_ihug.co.nz> wrote:
> Subject: Re: Nifty Find - HP2644A
>
>
> > 2. Has anyone ever seen a CRT develop mold between
> the
> > (bonded to the tube) safety glass and the tube
> itself?
>
> Steve et al
>
> This sounds like the problem I had a month or so
> back with the CRT in a
> HP9845. Only in my case the mould spots had
> 'advanced' inwards from the edge
> of the screen around 2-3 inches. Not pretty!
This is indeed what is happening to mine.
> If you have a look you will probably find the
> 'seal' around the edge of the
> front of the tube is taped over- virtually no real
> moisture barrier at all
> for what is underneath.
>
> Further- you will almost certainly find that the
> front of the tube itself
> has a conventional bonded safety glass- the mould is
> in the layer of
> transparent 'goo' used to attach an additional
> anti-glare 'cosmetically
> appealing' dark glass to the front of the safety
> glass on an ordinary CRT.
>
> The 'goo' in the case of the 9845 CRT was very
> similar in texture to silicon
> rubber-possibly was- and the layer was a bit over an
> eighth of an inch
> thick. Likewise the dark glass on the front.
>
> I tried several solvents on the 'goo' (after
> removing CRT from 9845 of
> course!) and found ordinary petrol to be fairly
> effective- there are no
> doubt better solvents but it worked.
>
> Judicious use of a piece of piano wire and weights
> was tried, with the CRT
> mounted in a temporary wooden frame, but the most
> rapid way to get the goo
> out was (you are outside or in a well ventilated
> area - right!) to dribble a
> generous amount of petrol into the goo- wait about a
> minute, and carefully
> dig out the softened stuff with a long thin
> screwdriver. It's tedious work
> and I did it in several stages but it was not
> difficult.
>
I'm a little nervous about screwdrivers or putty
knives and glass under vacuum. I wonder if a HEATED
wire would cut through this. Also, I've found that
acetone goes through just about anything not metal or
glass eventually.
If you've ever seen the people who replace car
windshields at work (on pre-1990's cars, anyway), they
heat a very thin wire with a blowtorch and use this to
cut the sealant. It might be hard to find this thin,
strong wire, though. Thin wire, easy. Strong wire,
easy. Thin, strong wire...
> End result- cleaned 'em up and got a perfectly
> useable CRT and separate
> 'anti glare' glass.
> I reassembled them with an air gap and 'goo' in the
> screen corners only-
I might use clear RTV or something similar, if I am
successful.
> its easy enuff to get into the gap and clean it out
> now- should the need
> arise again. Visually no difference- except maybe a
> bit brighter screen
> image.
> Essential point to note- make sure the tube has a
> bonded safety glass-- in
> this case it was difficult to actually tell till I
> had it out and removed
> all the black tape around the edge of the screen.
I think it is illegal in the US (at least for the last
40+ years) to sell a CRT without a bonded faceplate
(actually as a part of the glass). I was reading some
horror stories about what happened before this law.
Imagine a very hot tube of glass and metal (the gun
part of the tube) being shot right into your face
(because this is the direction it wants to go in when
the tube implodes). So I'm pretty sure that this will
be ok.
Considering that this tube might be hard to get,
probably expensive, and may not be or look "original"
without the faceplate, I think I'm going to make a
frame out of wood and try it. The CRT itself doesn't
seem to be burned at all, and delivers fairly crisp
characters.
Interesting that you did this so resourcefully - where
you are, I'll bet you can't get a replacement at ANY
price!
> DaveB
> Ch Ch NZ
>
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Received on Fri Sep 13 2002 - 22:50:01 BST