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2 Articles About Monitors Submitted By 4WL ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The Amstrad CTM640/644 colour monitors. *************************************** 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 *************************************** 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. ***************************************************************************** ***************************************************************************** Article 2 ~~~~~~~~~ Microvitec 14H94CGS2 Multiscan monitor. *************************************** 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.