61 lines
3.5 KiB
Plaintext
61 lines
3.5 KiB
Plaintext
Amiga 1080 Monitor Modifications
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A number of Amiga 1080 monitors were built by Toshiba. The people at
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Toshiba could have done a better job in a couple of respects:
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First, they did a poor job of extracting vertical sync pulses from the
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video signal that comes from the Amiga. This produces an error in the
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interlacing when the Amiga is used in 320x400 or 640x400 display modes.
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When you look closely at the screen you see alternating line spacings. It
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also gives characters a ragged look. The modification described in the
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dPaintII file reduces the interlace error by a factor of about 5.
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While interlaced video isn't the nicest thing to read characters on, it's
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neat to be able to put nearly all of a typewritten page on the screen. Most
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of the Amiga outlets handle a neat thing called Jitter-Rid, or some such
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thing. It is a thick piece of smoked plastic that goes on your 1080
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monitor. It enhances the contrast and attenuates the light from the screen
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to keep your brain from rattling too badly from the flicker. Also, dark
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characters on a light background seem to work best for me, anyway.
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The second problem is a thing called crossover distortion. They did a dumb
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thing that distorts the audio, even at very low volume levels. The Amiga
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deserves better sound. Unfortunately, this mod takes 2 diodes and a
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resistor, but it essentially eliminates the crossover distortion.
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If you aren't afraid of working on the average modern TV set, the 1080
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shouldn't prove to be much of a problem. Looking from the back, there are
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four screws, one at each corner. You need a long Philips screwdriver for
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those. There is a bottom plate that that also needs to come off. Finally,
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there is a screw just above the RGB input connector. Now, if you place the
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monitor face down on a soft towel, you can, with a little judicious prying
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and tugging, lift the rear part of the case off. Watch out for the speaker
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lead. You will have to unplug the connector before the back can come clear
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off.
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You will need to have something to support the neck of the CRT. A 1x4 about
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3-4 inches long worked pretty well. The whole assembly is pretty limber, so
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use reasonable caution. The main board on the bottom can be slid back along
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with all of the front-panel knobs. This permits access to the controls - you
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might as well squirt some contact cleaner in there while you are at it.
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If you are looking at the bottom, with the face of the CRT on your right,
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you will see a large IC that is the guts of the whole thing right in the
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middle of the board. C304 is visible above and to the left of the centerline
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of that humongous IC.
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The board that contains the audio output amplifier is on the left side of
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the 1080 if you are facing the screen. Looking at the underside of the
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board, the components you are looking for to do the audio mod are on the
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upper left corner.
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Fortunately, the P.C. boards have component numbers screened on them, so it
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isn't too hard to find the parts. I did the audio mod by lifting the
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collector lead of Q605 out of the hole and wiring directly to it. In
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retrospect, it probably would have been easier if I had just soldered an
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insulated wire to it, brought the wire through the hole and done all of the
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wiring on the backside of the board. If you are concerned about vibration
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messing up the "air-wired" connections, a shot of hot glue or some similar
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measure should put your mind at rest. The diodes are 1N914s from Radio
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Shack, but most any small-signal silicon diode should do.
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