Removing PVA from a CRT

Alan Perry aperry at
Mon Nov 19 15:01:51 CST 2018

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 <mailto:cctech at>> 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.

> Warner

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