CRT mold [was: HP2648 heartbreak]

From: Bob Shannon <bshannon_at_tiac.net>
Date: Sun Feb 13 12:51:02 2005

----- Original Message -----
From: "Vintage Computer Festival" <vcf_at_siconic.com>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk_at_classiccmp.org>
Sent: Sunday, February 13, 2005 10:38 AM
Subject: Re: CRT mold [was: HP2648 heartbreak]


<snip>

> Can you elucidate a bit on how the mold spots developed when you pried up
> the safety glass with the screw driver? Are you sure the spots weren't
> already there?
>

When you break the bond between the RTV-like material and the safety glass
shield, it "looks" very much the same as the mold spots.

I'm in the process of restoring the CRT for an Imlac that has a very bad
case of
whatever this problem is. It was so bad that sections of the clear bonding
material
could be pulled out from between the CRT face and the safety glass. These
bad
spots have a fine white powdery texture that may well be due to mold.

Using a tool to carefully reach between the safety glass and CRT face I've
removed
sections of the bonding material that were still 'good'. As you break the
bond and
any gas gets between the safety glass and bonding material you will see the
'spots'
even though the bonding material has not taken on that powdery texture.

It seems that the visual appearance problem is due to a failed bond, no
matter why
that bond failed.

Whatever is happening is effecting the bond between the safety glass and the
bonding
material itself. I've not yet seen this process take place between the CRT
and the
bonding agent for some reason.

It also seems that whatever this process is, once it starts to break the
bond between the
safety glass and bonding agent it becomes progressive and works from the
edges
inwards towards the center.

As for the bonding agent itself, I've heard that its a silicone based
material, and that
there is no practical solvent for it. It can be removed slowly by reaching
between the
safety glass and CRT with a thin hook while working from the side of the
CRT.

No need for hot wires or exotic solvents that might not work anyway. It
takes time
but some CRT's just are not available these days. I see no alternative to
solving this
restoration problem.

If your CRT is bad now, its not going to get any better with age.

Removing the old faceplate and failed bonding goo is not the biggest
problem. Finding
a good way to reattach the safety glass seems to be a larger issue.
Received on Sun Feb 13 2005 - 12:51:02 GMT