18 Oct
2011
18 Oct
'11
1:57 p.m.
Hello all,
I recall a while back a thread on dealing with screen rot on ADM-3a
terminals - surprising to me, because I have several of them and have
had no such issue. But I do have nasty looking spots on a HP 9845A
screen. Does anyone have specific experience with addressing this
problem on this machine? Just to be clear, it looks like round mold
colonies around the edges of the screen. It's likely that there's an
anti-glare coating and something colonized underneath it. Again, I'm
looking for specific details regarding this machine or another machine
of the era using the same screen technology, and how you eliminated the
colonies. :-)
I've (fortunately) never seen this problem 'in the flesh', although I am
told it can affect HP CRTs. Even my 2623 terminal is still perfect.
The front of the CRT is actually 2 pieces of glass bonded together, the
idea beign that it'll act like a car's laminated windscreen if the CRT
inmpodes and will prfecnt glass flying everywhere. The mould develops in
the bonding 'glue'.
There have bene several descriptions of how to cut through this glue and
separa the glass panels withput letting the vacuum out of the CRT.
Running a thin wire, possibly electrically heated, between them is the
scommon way.
But a word of warning. CRT implosion is not at all pleasant. It's perhaps
worth rememebrign that even in the 1940s and 1950s, when we didn't live
in a 'compensation culture', all TVs (or at least all those sold in the
UK) had a safet screen in fornt of the CRT (which did not have a
lamianted glass faceplate at that time). CRT implosion was very rate
(I've met one person who worked in a TV reapir shop and said it happned
to them _once_ in all his time working there), but it was obviouisly
serious enough that the mnufactuerers ddi soemthing about it.
And all the CRT data books I've looked in specifically say that no
attempt must be made ot remvoe the bonded galss faceplate.
Now, as you knowe I gernally approve of repairing rather htan replacing,
so I am not going to suggest you should't try to remvoe the safety glass.
But I do feel that removing it and leaving it out, as some have
suggested, is downright irresponsible. If you remvoe it, you need to
rebond it to the CRT, and make sure the bond is osound. I wonder if the
optical adhasives used for bonding lens elements (the ones that cure
under UV light) are good for this?
I don't baev a 9845A, only a 9845B, and that with the enhanced mono
monitor. But if that's anythign to go by, while there's some complex
circuitry in the monitor (much fo the video generation logic is there),
the actuall monitor seciton -- the CRT and its drivers -- are fairly
convnetional. Is there any reason not to consider replacing the CRT in
your machine?
Thanks -- Ian
-tony