Re: Removing PVA from a CRT

[ED SHARPE via cctalk]

Saving this  thread!
Thanks  for the great info and hints  as we have a stack of HP  254x terminals  
and some of them  graphics  hi end  ones... have  no idea if they  will light 
off for  not but thankful to have  even as  static  displays. 


Ed Sharpe  Archivist for  SMECC  
 
 
 
 
 
In a message dated 11/25/2018 12:27:56 PM US Mountain Standard Time, 
cctalk@classiccmp.org writes:

 
>

> The heat pads are worth a shot if they can maintain temp long enough to do
> the job, though you'll be up against quite a bit of thermal mass with that
> thick glass. The old trick that people are still using today with vintage
> 21" CRT's is to put them in a kiddie pool outside and let the sun warm the
> water. You don't want to start too hot for risk of cracking the glass.
> *Glances out window* I can tell you that trick wouldn't work here today,
> nor for 6 more months.
>
> If you have a way of ensuring the optically clear adhesive sheet bonds
> evenly and won't yellow, I don't see why that wouldn't work. I recall
> someone did do the foam tape/packing tape operation and then DID fill the
> void with a PVA type liquid material. Risky to ensure all the air bubbles
> made their way out, for sure. -C
>
>
>

I did some tiny bit of research into this when I dealt with my HP2640 B and
a VR201. The former was in a condition where just a tiny fraction in the
middle of the screen attached to the glass so it almost fell of by itself.
With the VR201 the story was a bit different. I didn't want to heat it up
like most people seems to be doing when looking at the Youtube clips. I
checked the solubility of the PVA (PVAc really, PVA is something different)
in water and nothing happened at all. I tried to heat the water a bit but
no change. I am not sure how come people are successful with this method.
But I investigated PVAc a bit and found out that it is soluble in various
esters. I bought a bottle of Butylacetate and indeed it made it dissolve
quite well. Butylacetate is mostly used as as solvent for polyester paints,
and I think it is an ingredient in what women use for removing nail polish
(when not using acetone). BTW Acetone is also dissolving PVAc very well but
the boiling temperature is much lower. As far as I can understand
Butylacetate is not very harmful to deal with either.

What I did wash to inject butylacetate using a long needle syringe in
between the front glass and the CRT and let it rest for a few days. I put
some plastic wrap around to contain the butylacetate a bit more and then I
repeated it a couple of times until the front glass simply fell off.

This is the method I will use in future with my other screens that have the
same problem (HP2645, HP9835, HP9845, (Possibly also the Tektronix 4016
depending on the type of front glass used).

/Mattis

Re: Removing PVA from a CRT

[Mattis Lind via cctalk]

>
> The heat pads are worth a shot if they can maintain temp long enough to do
> the job, though you'll be up against quite a bit of thermal mass with that
> thick glass. The old trick that people are still using today with vintage
> 21" CRT's is to put them in a kiddie pool outside and let the sun warm the
> water. You don't want to start too hot for risk of cracking the glass.
> *Glances out window* I can tell you that trick wouldn't work here today,
> nor for 6 more months.
>
> If you have a way of ensuring the optically clear adhesive sheet bonds
> evenly and won't yellow, I don't see why that wouldn't work. I recall
> someone did do the foam tape/packing tape operation and then DID fill the
> void with a PVA type liquid material. Risky to ensure all the air bubbles
> made their way out, for sure. -C
>
>
>

I did some tiny bit of research into this when I dealt with my HP2640 B and
a VR201. The former was in a condition where just a tiny fraction in the
middle of the screen attached to the glass so it almost fell of by itself.
With the VR201 the story was a bit different. I didn't want to heat it up
like most people seems to be doing when looking at the Youtube clips. I
checked the solubility of the PVA (PVAc really, PVA is something different)
in water and nothing happened at all. I tried to heat the water a bit but
no change. I am not sure how come people are successful with this method.
But I investigated PVAc a bit and found out that it is soluble in various
esters. I bought a bottle of Butylacetate and indeed it made it dissolve
quite well. Butylacetate is mostly used as as solvent for polyester paints,
and I think it is an ingredient in what women use for removing nail polish
(when not using acetone). BTW Acetone is also dissolving PVAc very well but
the boiling temperature is much lower. As far as I can understand
Butylacetate is not very harmful to deal with either.

What I did wash to inject butylacetate using a long needle syringe in
between the front glass and the CRT and let it rest for a few days. I put
some plastic wrap around to contain the butylacetate a bit more and then I
repeated it a couple of times until the front glass simply fell off.

This is the method I will use in future with my other screens that have the
same problem (HP2645, HP9835, HP9845, (Possibly also the Tektronix 4016
depending on the type of front glass used).

/Mattis

Re: Removing PVA from a CRT

[Michael Thompson via cctalk]

>
> Date: Mon, 19 Nov 2018 10:41:36 -0800
> From: Alan Perry 
> Subject: Removing PVA from a CRT
>
> 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.
>
> alan
>

When we fixed the VR14 at the RICM, we were concerned about the safety
aspects of removing the PVA and just using double-sided tape to hold the
outer glass in place. We bought a thin sheet of Lexan at Home Depot, put
the outer glass on a cookie sheet with the outside surface down, put the
sheet of Lexan on top, and put it in an oven. When the temperature hit 420F
(if I remember correctly) the Lexan softened and conformed to the inside of
the glass. We trimmed the Lexan to size, reassembled the Lexan and glass to
the front of the CRT, and glued the steel mounting band in place. It looks
great, and is probably a lot safer than just leaving the PVA out.

-- 
Michael Thompson

Re: Removing PVA from a CRT

[Curious Marc via cctalk]

I like this idea, thanks for sharing. I might do the same for my HP 264x 
screens.

Marc

 

From: cctech  on behalf of 
"cct...@classiccmp.org" 
Reply-To: Michael Thompson , 
"cct...@classiccmp.org" 
Date: Tuesday, November 20, 2018 at 5:59 PM
To: "cct...@classiccmp.org" 
Subject: Re: Removing PVA from a CRT

 

When we fixed the VR14 at the RICM, we were concerned about the safety

aspects of removing the PVA and just using double-sided tape to hold the

outer glass in place. We bought a thin sheet of Lexan at Home Depot, put

the outer glass on a cookie sheet with the outside surface down, put the

sheet of Lexan on top, and put it in an oven. When the temperature hit 420F

(if I remember correctly) the Lexan softened and conformed to the inside of

the glass. We trimmed the Lexan to size, reassembled the Lexan and glass to

the front of the CRT, and glued the steel mounting band in place. It looks

great, and is probably a lot safer than just leaving the PVA out.

 

-- 

Michael Thompson

 

Re: Removing PVA from a CRT

[Cory Heisterkamp via cctalk]

On Nov 19, 2018, at 7:28 PM, Alan Perry wrote:

> In the video that I looked at, the guy cut 8 1/8" pieces of double-sided foam 
> tape, three each along the top and bottom and one on each side, then sealed 
> it with clear packing tape. It seemed to me that using some optically clear 
> adhesive sheet would accomplish both jobs.
> 
> I have some heat pads (gel in plastic that gets thrown in a microwave to heat 
> up) for loosening the screen adhesive on iPads and such. Can I use them to 
> get the remaining PVA to loosen up?
>> 
> 


The heat pads are worth a shot if they can maintain temp long enough to do the 
job, though you'll be up against quite a bit of thermal mass with that thick 
glass. The old trick that people are still using today with vintage 21" CRT's 
is to put them in a kiddie pool outside and let the sun warm the water. You 
don't want to start too hot for risk of cracking the glass. *Glances out 
window* I can tell you that trick wouldn't work here today, nor for 6 more 
months.

If you have a way of ensuring the optically clear adhesive sheet bonds evenly 
and won't yellow, I don't see why that wouldn't work. I recall someone did do 
the foam tape/packing tape operation and then DID fill the void with a PVA type 
liquid material. Risky to ensure all the air bubbles made their way out, for 
sure. -C

Re: Removing PVA from a CRT

[Alan Perry via cctalk]

In the video that I looked at, the guy cut 8 1/8" pieces of double-sided 
foam tape, three each along the top and bottom and one on each side, 
then sealed it with clear packing tape. It seemed to me that using some 
optically clear adhesive sheet would accomplish both jobs.


I have some heat pads (gel in plastic that gets thrown in a microwave to 
heat up) for loosening the screen adhesive on iPads and such. Can I use 
them to get the remaining PVA to loosen up?


On 11/19/18 1:10 PM, Cory Heisterkamp wrote:
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 
mailto:cct...@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
> mailto:cct...@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=81c3e1ded7cb1eb6b9d1200a604d9889=5C7778F1

alan
>
> Warner

Re: Removing PVA from a CRT

[Alan Perry via cctalk]

On 11/19/18 1:48 PM, Paul Koning wrote:



On Nov 19, 2018, at 4:01 PM, Alan Perry via cctech  
wrote:





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=81c3e1ded7cb1eb6b9d1200a604d9889=5C7778F1

alan

It looks like you turned the intensity up so far that the retrace didn't get 
blanked fully.  Not much choice about that given the bad screen, I suppose.


Actually, the intensity is turned all of the way up because that is 
where it happened to be when I connected everything up. I was so focused 
on whether DOS had booted that it didn't even click in my head that I 
could adjust the monitor to make it easier to read. I didn't notice that 
I had things turned all the way up or even notice the retrace lines 
until later when I looked at that picture.


alan

Re: Removing PVA from a CRT

[Warner Losh via cctalk]

On Mon, Nov 19, 2018 at 11:41 AM Alan Perry via cctech <
cct...@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?

Warner

Re: Removing PVA from a CRT

[Cory Heisterkamp via cctalk]

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 
wrote:

>
>
> On 11/19/18 12:18 PM, Warner Losh wrote:
> >
> >
> > On Mon, Nov 19, 2018 at 11:41 AM Alan Perry via cctech
> > mailto:cct...@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=81c3e1ded7cb1eb6b9d1200a604d9889=5C7778F1
>
> alan
> >
> > Warner
>
>

Re: Removing PVA from a CRT

[Alan Perry via cctalk]

On 11/19/18 12:18 PM, Warner Losh wrote:



On Mon, Nov 19, 2018 at 11:41 AM Alan Perry via cctech 
mailto:cct...@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=81c3e1ded7cb1eb6b9d1200a604d9889=5C7778F1

alan


Warner

Removing PVA from a CRT

[Alan Perry via cctalk]

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?

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?

alan 

Re: Removing PVA from a CRT

[Glen Slick via cctalk]

On Mon, Nov 19, 2018 at 10:41 AM Alan Perry via cctech
 wrote:
>
> 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 around a dozen or so HP 264x terminals with various states of
CRT decay. Most have developed bubbles in the face of the CRT. Some
are bad enough that the CRT has started leaking goo from the face.

I have no experience doing any cleanup work on these CRT issues. We
should have a CRT restoring party. Anyone else in the Seattle area
have "moldy" CRTs that need some attention, and/or have experience
doing the work?

Re: Removing PVA from a CRT

[Christian Corti via cctalk]

On Tue, 20 Nov 2018, Michael Thompson wrote:

the glass. We trimmed the Lexan to size, reassembled the Lexan and glass to
the front of the CRT, and glued the steel mounting band in place. It looks
great, and is probably a lot safer than just leaving the PVA out.


You removed the steel band??? *That* is the implosion protection of a CRT.

Christian