Nifty Find - HP2644A

From: Dave Brown <tractorb_at_ihug.co.nz>
Date: Fri Sep 13 17:20:01 2002

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!
 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.

 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-
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.

DaveB
Ch Ch NZ
Received on Fri Sep 13 2002 - 17:20:01 BST