On Wed, 2009-04-22 at 10:47 -0600, Richard wrote: Nope, I've never even seen this "screen rot" on any tube. Maybe we don't get it in the UK? Gordon

--- On Wed, 4/22/09, Jules Richardson <jules.richardson99 at gmail.com> wrote: It only happens on tubes with a laminated safety glass front faceplate. Most picture tubes use a tensioned rimband for implosion protection. Some early ones, however, used a bonded faceplate. It's glued to the front of the tube with a PVA compound. Over time, with mold/mildew/something eats away at this compound, leaving the "rotted" appearance, and causing it to delaminate from the front of the tube itself. This also happens to old color television sets - the early ones using 21FJP22 especially. The TV collector community refers to it as 'cataracts'. To fix it, you must remove the bonded faceplate from the tube completely, and clean out the gunk. On TV tubes, this is done by placing the tube neck-down in a plastic trash can (so the neck is safely suspended inside), and heating the CRT face with a heat gun. Once you get the bonding agent hot enough, you can seperate the faceplate from the tube without breaking either. Then clean out the gunk with heat/solvents, and reattach the faceplate using packing tape around the edges, leaving a simple air gap between the face of the tube and the faceplate. Some types of tubes (usually Zenith branded) have a different bonding agent that doesn't react to heat - those require a different approach. Namely, a hot nichrome wire to slice between the faceplate and tube face. I've not tried fixing this on a computer terminal before, but I have an ADM3A in dire need of this. -Ian

I have two DEC VR201 mono monitors. They both had the blue spot particularly at the edges. The spotting exists within the adhesive that bonds the outer faceplate to the screen. The layer of goo is quite thick. (About 2-3 millimeters) The result is something akin to a car shatterproof windscreen. The extra faceplate is not part of the original tube spec and would have been added by DEC later. I simply prised off the front faceplate in bits knowing it would not shatter as it was stuck to the goo. Peel off the goo on the screen, clean, adjust the cutoff pot and the result is a bright clear display. (Don't try this if you are not comfortable working with CRT's) There is a small gap between the bezel and the tube (extra cooling?) but the rubber tube spacers mean nothing is loose. Regards Rod Smallwood I collect and restore old computer equipment with this logo. ??????????????? ?d?i?g?i?t?a?l? ??????????????? -----Original Message----- From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org] On Behalf Of Jules Richardson Sent: 22 April 2009 20:25 To: General Discussion: On-Topic and Off-Topic Posts Subject: Re: Reforming caps and CRTs Gordon JC Pearce MM3YEQ wrote: I've seen it on lots of HP terminals in the UK, and there's also a Digico terminal at Bletchley which has a very bad case of it. I don't remember ever seeing it on Tek / Apollo / Sun / SGI / DEC / Acorn displays, PC monitors, or low-end 40/80 column displays for vintage home micros - maybe it'd be possible to narrow it down to a specific manufacturer, model range or whatnot... cheers Jules

On Wed, 2009-04-22 at 15:43 -0500, Jules Richardson wrote: You could buy them new, at least as recently as the mid-90s. The gun looked pretty much as you'd expect - a flat glass disc with a long glass tube sticking out between the pins, and the gun assembly exposed. Some had about 2" of "neck" around the gun, presumably because you needed to weld the glass differently. Gordon