2 Articles About Monitors Submitted By 4WL
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The Amstrad CTM640/644 colour monitors.
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I decided to give a bit more information about the CTM640/644 monitors as
someone rightly questioned their TTL compatibility. Firstly it's not correct
to say that all Acorn computers produce too bright a display with all these
monitors and in my experience all 8bit Acorn computers produce a usable
display by direct connection. However this picture can be adjusted for ideal
contrast/brightness with resistors for those computers which produce a very
strong signal. In an ideal world all Acorn's computers with the standard 6pin
RGB connector would have identical signal levels, this however is not true.
It varies with different models and possibly different issues of the same
model. Perhaps even models of the same issue although I've never experienced
this. The Electron I believe has the weakest output and instead of using
resistors you will have to open the monitor and adjust the pot at the back
for increased brightness or at least that's my experience.
The Amstrad CPC computers (excluding the later Plus range) have a palette of
27 colours. They do this by applying the bright signal to each separate gun
(red, green or blue). So for example Red can be off, normal or bright. That's
three variations for each gun. 3x3x3=27. However normal TTL signals are
2x2x2x2=16. This is because there's the three guns plus the overall
brightness signal which effects all three guns at once.
The original Spectrum 128 computer had a TTL output RGB socket with a
separate brightness signal. The later Plus 2 model (when Amstrad took over
Sinclair) incorporated the brightness signal into the main Red, Green and
Blue signals. It still only produced sixteen colours as this was the
spectrum standard. Connecting either a 128 or Plus 2 to the same monitor
will result in a display of similar brightness and the levels are almost
identical.
The Amstrad CTM monitors are extremely simple in design. The signal it
receives on each pin (red, green or blue) is not processed to check if it's
TTL or Analogue, it's just sent straight on.
It's also worth remembering the lower the brightness setting you use the
longer the tube will last.
Remember if you're making up a cable with resistors and they are not quite the
right value, i.e. the picture is too bright or too dark, by putting resistors
of the same value in series you double the resistance and putting them in
parallel halves resistance. Series meaning one after the other and parallel
meaning side by side.
Computers that work with the CTM640/644
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Acorn 8bit range, Archimedes, Atari ST, Spectrum 128 range, Amiga range, Sam
Coupe, Oric, Lynx, Megadrive, Super Nintendo, Amstrad CPC range (obviously).
Basically almost anything with RGB output except modern PCs.
In summary I would say that these Amstrad monitors are pitched just slightly
below TTL levels meaning resistors for optimum performance with TTL
computers and possibly internal adjustment for analogue computers. Of course
the brightness control is a variable resistor itself which governs the
amount of signal that reaches the tube. Ideally you should set that at
half way and fit resistors to the cable that give a normal display.
Lastly, I have also found these monitors to work happily at 60hz although the
vertical hold will need to be adjusted. There may be a point on the vertical
hold where you can get both 50hz and 60hz to work without adjustment.
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Article 2
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Microvitec 14H94CGS2 Multiscan monitor.
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The model number is probably generally known as a 1494 but the above is what
is written on the back of the monitor. I thought I'd write a little review
of it as I'm quite impressed with it. I didn't buy it new but I got it in as
new condition. This isn't a current model as it's since been replaced by a
cheaper restyled version. I expect the new model is broadly similar. This
model was originally sold between £399 and £449. The replacement model
sells at £299 to £329. Microvitec are obviously famous to BBC users as they
supplied the vast majority of monitors to schools who bought BBCs. They have
a reputation for being a bit crude but reliable. The company itself has a
reputation for ignoring any letters you send them as has been the
experience of myself and others that I have spoken to. They're a British
company who I believe are independent. They basically design and assemble a
monitor around a Japanese tube.
The monitor itself has a beige and light brown case with a swivel/tilt stand
built in. There's a normal power connector socket at the back plus a 9pin D
socket for the computer connection. The front has one hinged flap that hides
the brightness and contrast control plus the buttons for framing the
picture. The styling is bland but not unattractive. Microvitec don't seem
to have very good stylists and really this is the firms main failing. Their
competitors Philips and Sony do a much better job of styling. Also Philips
and Sony use Trinitron tubes in their monitors as does Taxan. Obviously Sony
do because they invented the Trinitron tube. Trinitron seems to be the
accepted standard for top of the range computer monitors. I personally don't
rate the Trinitron tube because of the infamous Trinitron lines that occur
horizontally across the screen one third down and two thirds down. These
lines which are mainly hidden on most screen displays, become prominent at
certain brightness and contrast levels. They are basically two thin lines
within the tube that remove the electrical charge from the screen.
The Microvitec's dot pitch is 0.28 using a conventional tube. This is
reasonably standard for multisyncs using conventional tubes with a 14" screen
size. A Trinitron of the same size would be 0.26 or worse. The lower the
number the better. Some cheaper multisyncs would have a 0.39 dot pitch. The
display itself is razor sharp on the Microvitec. Multisync is a general term
and a little vague. A normal television is single sync although many
televisions also allow 60hertz making them dual sync. Anything over dual
sync are called multisync even though some only allow three syncs and others
are variable over a wide range. The Microvitec is a true multisync. It
accepts anything upto full SVGA even allowing for strange non standard modes
like the Atari STs high resolution mode (640x400). It has a memory system so
you can set up a screen mode exactly as you like it and store it.
Unfortunately this system doesn't use presets so you can choose which one
you want. It does it by frequencies so in effect you have to alter it if you
have let's say a PC and an Archimedes as they both generate the same
frequencies in certain modes. On normal TV sync modes you cannot remove the
side borders that you would get on a normal TV display. On the Archimedes
you can eliminate the borders by choosing an overscan mode and sizing it
down to fit the screen. Higher sync modes allow you to eliminate borders
easily, mainly because PC displays have less of a border anyway.
Anyway I'm pleased with the monitor. I can use the same monitor with many
different computers. As long as they have some sort of RGB output they're
compatible.
Recommended if you see one in good nick going cheaply.