While we're talking about CRTs, I want to ask if anyone has heard of
any problems with Digital VGA monitors, about 4 years old. We
installed a lab full of them, and when I turned them on, two lost the
magic white smoke, and more have various other problems.
>> Is this related to what I am about to ask? Could somebody do a short
>> summary of why Fimi(?) greyscale megapixel NeXT monitors fade after
>
>Fimi monitors seem to be related to Philips, but just try getting a
service
>manual for one.
>
>> 20,000 or so hours of use and indicate whether there are any other
>> monitors (perhaps some classic) that show similar problems?
>
>The most likely cause is the CRT cathode is losing emission (basically
>it's not sending enough electrons to the screen). But it could also be
a
>low electode voltage on the CRT, a problem with the brightness control,
etc.
>
>It's time to mention a trick that's saved me a lot of time over the
>years, even though it's too late for you to use it. When I get a
monitor,
>whether new, or part of a classic computer, or whatever, the first
thing
>I do is pull the case and note down the CRT electrode voltages and any
>other testpoints I think might be useful (PSU outputs, etc). If I have
a
>service manual/schematic, then I note them in there. If not, then it's
>normally easy to find the CRT pinouts at least and I write down the
>voltages in a suitable place, such as the user manual. Even a label
stuck
>inside the case.
>
>Then, if the picture starts to fade, I can check the voltages again to
>see if there are any problems.
>
>OK, if it is the CRT emission (and I've had this happen on large mono
>monitors), then you may be looking for a new CRT. There are CRT
>reactivation devices (basically they run the heater at about 20%
>overvoltage and apply a high voltage, about 200V, between the cathode
and
>1st grid), but modern CRTs don't normally respond too well. Sometimes
>overrunning the CRT heater all the time (it's unlikely you'd burn it
out)
>will help. There are all sorts of tricks for that, including wrapping a
>couple of turns of wire round the core of the flyback and connecting it
>in series with the heater supply. If the heater is already supplied by
>the flyback, then you need to try the new winding both ways round. The
>way that brightens the heater and picture is the right one.
>
>Incidentally, a lot of micros, video terminals, etc use 12" mono CRTs.
>There are basically only 2 types - thin neck, 7 pin, 11V heater and
thick
>neck, 8 pin, 6.3V heater. A good source of the former is old portable
>TVs. If you can get a portable TV with a good tube, perhaps with
flyback
>or tuner problems, the CRT will probably go into a TRS-80 Model 3 or a
>VT100, or.. with only a few mods, if any.
>
>
>>
>>
>> -- Stephen Dauphin
>>
>
>
>-tony
>
>
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Received on Mon Nov 02 1998 - 20:26:48 GMT