13 Sep
2002
13 Sep
'02
3:50 p.m.
Very interesting! Thanks - comments below.
--- Dave Brown <tractorb(a)ihug.co.nz> wrote:
Subject: Re: Nifty Find - HP2644A
This is indeed what is happening to mine.
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! 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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