HP CRT mould update

Jules Richardson julesrichardsonuk at yahoo.co.uk
Sun Apr 17 13:11:21 CDT 2005


On Sun, 2005-04-17 at 10:13 -0700, Vintage Computer Festival wrote:
> On Sun, 17 Apr 2005, Jules Richardson wrote:
> 
> > I've just removed the faceplate on the CRT for an HP 250 that was
> > suffering from the dreaded mould. Used a bit of resistance wire as
> > someone here had suggested, and it was a remarkably easy job.  Took
> > about ten mins to make it all the way across the CRT (although I was
> > only running from a 10V DC supply - I expect there's a lot of scope for
> > increasing the voltage without risk of damaging the CRT)
> >
> > The sealant stuff pretty much just peels straight off the front of the
> > CRT / rear of the faceplate once the two are separated.

> Thanks for the info.  Did you save any of the affected scraps to have
> analyzed by a biologist or something? 

Hmm, nope - but they're just in the bin outside (contained within the
newspaper on which I was working) so if someone does know someone I
could retrieve a piece...

> Are you certain it was a mold eating at the sealant 

Actually, there was no obvious mould as such on this one - it seemed
more like the sealant had turned to liquid in some places (visible as
'puddles' behind the glass), whilst in others it seemed to have
crystalised into small hard lumps (giving the visible white spots)

So, no sign of visible mould - I wonder if the dark spots sometimes seen
are maybe some form of optical effect; trapped bubbles as you say rather
than being something physically dark in colour. 

Our other HP 250 display shows far more signs of the dark 'mould' spots,
so maybe I'll give that one a go now that I know the procedure works.

> > I'm not sure about trying to re-seal it; that could go horribly wrong
> > and leave air bubbles trapped in there. Not even sure what stuff to use.
> > Padding the faceplace out as necessary right at the edges (where it
> > won't be visible when everything's back together) is probably the best
> > course of action and it'll look as good as new when back together.
> 
> If you don't introduce some sort of filler you might have a shadow or
> annoying opitcal affect.  Possibly.

Hmm, good point. Initially I think we're just going for a static display
anyway, because there are more pressing projects to sort out than this
machine - so it won't be an issue until someone has time way down the
line to actually restore the machine to working condition.

Maybe I should try this same procedure on one of our HP terminals that
have the same problem though, then I can mess around with fillers on
those (or see how well it works without). 

> > Next interesting task will be getting the paint off the 250's console
> > desk though - seems like when they were scrapped someone just went
> > around with a spray-can and put big X's on anything that was being
> > disposed of...
> 
> Gasoline (or petrol as you might want to call it :) is supposed to be able
> to dissolve spraypaint without affecting the underlying paint. 

Interesting, I'll give that a try on a test area somewhere - luckily the
spray painters missed the built-in keyboard area! Mainly worried about
whatever I use to remove the paint damaging the underlying console table
material...

cheers

Jules




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