Amiga Essay, Research Paper
Amiga 1080 Monitor Modifications
A number of Amiga 1080 monitors were built by Toshiba. The people at
Toshiba could have done a better job in a couple of respects:
First, they did a poor job of extracting vertical sync pulses from the
video signal that comes from the Amiga. This produces an error in the
interlacing when the Amiga is used in 320×400 or 640×400 display modes.
When you look closely at the screen you see alternating line spacings. It
also gives characters a ragged look. The modification described in the
dPaintII file reduces the interlace error by a factor of about 5.
While interlaced video isn’t the nicest thing to read characters on, it’s
neat to be able to put nearly all of a typewritten page on the screen. Most
of the Amiga outlets handle a neat thing called Jitter-Rid, or some such
thing. It is a thick piece of smoked plastic that goes on your 1080
monitor. It enhances the contrast and attenuates the light from the screen
to keep your brain from rattling too badly from the flicker. Also, dark
characters on a light background seem to work best for me, anyway.
The second problem is a thing called crossover distortion. They did a dumb
thing that distorts the audio, even at very low volume levels. The Amiga
deserves better sound. Unfortunately, this mod takes 2 diodes and a
resistor, but it essentially eliminates the crossover distortion.
If you aren’t afraid of working on the average modern TV set, the 1080
shouldn’t prove to be much of a problem. Looking from the back, there are
four screws, one at each corner. You need a long Philips screwdriver for
those. There is a bottom plate that that also needs to come off. Finally,
there is a screw just above the RGB input connector. Now, if you place the
monitor face down on a soft towel, you can, with a little judicious prying
and tugging, lift the rear part of the case off. Watch out for the speaker
lead. You will have to unplug the connector before the back can come clear
off.
You will need to have something to support the neck of the CRT. A 1×4 about
3-4 inches long worked pretty well. The whole assembly is pretty limber, so
use reasonable caution. The main board on the bottom can be slid back along
with all of the front-panel knobs. This permits access to the controls – you
might as well squirt some contact cleaner in there while you are at it.
If you are looking at the bottom, with the face of the CRT on your right,
you will see a large IC that is the guts of the whole thing right in the
middle of the board. C304 is visible above and to the left of the centerline
of that humongous IC.
The board that contains the audio output amplifier is on the left side of
the 1080 if you are facing the screen. Looking at the underside of the
board, the components you are looking for to do the audio mod are on the
upper left corner.
Fortunately, the P.C. boards have component numbers screened on them, so it
isn’t too hard to find the parts. I did the audio mod by lifting the
collector lead of Q605 out of the hole and wiring directly to it. In
retrospect, it probably would have been easier if I had just soldered an
insulated wire to it, brought the wire through the hole and done all of the
wiring on the backside of the board. If you are concerned about vibration
messing up the “air-wired” connections, a shot of hot glue or some similar
measure should put your mind at rest. The diodes are 1N914s from Radio
Shack, but most any small-signal silicon diode should do.