Removing PVA from a CRT

[Cory Heisterkamp]

Those retrace lines are likely an artifact of the brightness control being
set too high. It's pretty typical with older monochrome TV sets. It also
looks like there's insufficient vertical sweep, probably due to old
capacitors.

On a CRT that small, I wouldn't be concerned about direct fitting the
safety glass over the CRT. In fact, if it has an implosion band, that outer
glass could possibly be for glare reduction only. Some TV collectors use
foam tape around the perimeter of the CRT face as a cushion, then seal the
glass to the face with a good quality tape.

The good news is that PVA is so bad that an hour soak in a tub of warm
water should do the trick. -C

On Mon, Nov 19, 2018 at 3:02 PM Alan Perry via cctech <cctech at classiccmp.org>
wrote:

>
>
> On 11/19/18 12:18 PM, Warner Losh wrote:
> >
> >
> > On Mon, Nov 19, 2018 at 11:41 AM Alan Perry via cctech
> > <cctech at classiccmp.org <mailto:cctech at classiccmp.org>> wrote:
> >
> >
> >     I recently picked up a Rainbow 100. The PVA between the safety
> >     glass and the CRT on VR201 that came with it has broken down and
> >     failed badly.
> >
> >     I have seen videos and read about removing the safety glass,
> >     cleaning out the PVA, and reattaching and resealing the safety glass.
> >
> >     All that I have seen basically sticks the safety glass on at its
> >     edges and leaves a void where the PVA had been. It seems to me
> >     that the PVA was providing some implosion protection. Would it
> >     work to replace the PVA and attach the safety glass to the tube
> >     with an optically clear adhesive sheet? I have seen that this
> >     exists, but have never used it before.
> >
> >     Also, I have never worked on a CRT before. I am trying to find a
> >     local person who can observe me and stop me from doing something
> >     stupid. If I can’t find someone, what am I more likely to do
> >     wrong? How can I be sure I discharged it before touching it?
> >
> >
> > I have a VR201 that's like this myself, and I've been too scared to
> > try to fix it. Instead, I've tried bodging together various hacks to
> > try to get the signal into a modern composite to VGA converter...
> >
> >     Finally, a VR201 specific question. I booted the Rainbow over the
> >     weekend and, looking through broken-down PVA, I could see the
> >     Rainbow has booted and I could enter DOS commands. I could also
> >     see white retrace lines. What is the likely cause of that on a
> >     35-year-old CRT?
> >
> >
> > Pics?
>
> Here is an attempt to use Facebook for image hosting here. If it doesn't
> work, I will put the image up on a real image hosting site.
>
>
> https://scontent-sea1-1.xx.fbcdn.net/v/t1.0-9/46508514_10156808244977208_2306314600917762048_n.jpg?_nc_cat=105&_nc_ht=scontent-sea1-1.xx&oh=81c3e1ded7cb1eb6b9d1200a604d9889&oe=5C7778F1
>
> alan
> >
> > Warner
>
>