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Amnesia 8
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Amnesia - Issue 08 (1992-05-31)(Eclipse).adf
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1992-05-31
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8KB
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166 lines
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| TELEVISION AND THE 1081 MONITOR |
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| ...... D.I.Y. TV TUNER ...... |
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| ...... by Steve Wright ...... |
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I rather like the idea of having my 1081 monitor double as a
T.V. at times when the Amiga is heavily engaged in doing dull and boring
tasks (dull and boring to the eye that is) or just purely as a T.V.
monitor when the thought of shooting up green meanies doesn't turn you
on. For example, when compile time is the same as news time - why not
have both?
Most have done this by using the video out signal from their
video recorder. That's O.K. if you have a spare video machine laying
around doing zilch or a rich auntie Gladys who eventually takes the hint
and gives you one for your birthday. If you're like me and have neither,
there is a way to have VIP working and ALF yelling for around $60.
Cheap T.V. tuners are not easily found. Tuner modules are a little
more plentiful, but not much use on their own, and some of these were
fairly expensive. Then looking through a monthly electronics mag I saw an
ad for a Teletext tuner kit, price $59.95. So down I went to the store
and upon inspecting the docs I decided to buy and try. Hmmm, video out,
sound (mono), VHF & UHF range, seems just what I was looking for.
The kit was complete with all components, assembled tuner module,
P.C. board, tuning pot, transformer and docs. The unit was originally
intended to be inserted in a teletext module (also a kit), so a few extra
parts are necessary for our purpose. Namely :-
a box to house it in (I housed mine in a 200*110*60 jiffy box),
power switch (240V rated and preferably illuminated),
75 ohm T.V. socket, 2 RCA sockets (one for each of the video and sound
outs), and small amount of wiring. The kit also came with a large decal
which I cut down to suit, this gave the unit a neat front panel that
didn't have that home made look.
It won't be necessary for me to explain the assembly of the kit
as the docs which come with it are very good. Converting it for our
purpose is a piece of cake as well. The docs show where the three points
are (video out, sound out, aerial in). So basica lly all that's needed to
be done is find these points and wire them up to their corresponding
sockets, easy. Ventilation is necessary as it does get quite warm, drill
holes in the jiffy box for this or buy a ventilated box maybe easier.
I guess I spent about 10-12 hours on it, but I've been told that
I'm a bit of an old woman on these things, so it may not take that long
for you.
There was a snag though (isn't there always?) on completion. I
had a beautiful clear picture on all channels but jumping intermittently.
I found that the sync level was too low and at times losing it, causing
the jumping. Enquiries from where I bought it found that an errata sheet
was available to fix the problem. It involved a small alteration to the
P.C. board. Make sure your kit has this errata sheet.
The kit I purchased was a Dick Smith Teletext tuner module kit, part
number K6319, price $59.95. I checked availability at time of writing and
they tell there are plenty of them. The other parts used are common
components (sockets, switch, wiring,box) and can be purchased anywhere.
-----------------
Now, this where the story normally ends, unfortunately in this
case it doesn't. When connecting the video out from your new tuner to the
CVBS IN on your 1081 monitor and the same for the sound, you will be
graced with a crisp clear picture any TV buff wo uld be proud of, but
turning on the computer will send the screen crazy. Why? Well, when we
connect the tuner to the CVBS IN we can switch the video signal in and
out via the front switch (CVBS/RGB) but this is not switching the sync
signals on and off. The two sync signals together are causing the crazy
picture when switched to CVBS mode. It can be fixed though, and quite
easily.
We need to switch the sync line on the RGB to off when we
require the video to be viewed (CVBS ON). Luck has it that the CVBS/RGB
switch is a two pole switch of which only one is used. Lets cut the PCB
track leading to pin 20 of the RGB socket and run two wires from either
side of the cut track and connect them to the unused pole of the switch.
Note that the tracks leading from the unused pole go to holes where no
parts have been fitted. The wiring should be shielded cable earthed at
one end, preferably at the rear for ease of access. There it is, easy
wasn't it! If you don't agree or feel confident with this mod, someone
with electronics experience &/or someone who has already done this mod
will have it done in no time (ask your local user group).
Note that the mod described is for a 1081 not the 1084. The 1084
is totally different in its construction. The sync signals are paired
together and not buffered as on the 1081. I've heard of a successful mod
done for the 1084 and it didn't sound all that difficult. Not having
access to a 1084 monitor to try and test I can't offer much comment. Is
there anyone out there who can ?
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There is one other thing that can be done concerning the sound
from the tuner as an option. You will notice that the sound level from
the tuner is much higher than that from the Amiga and when mixed together
(the CVBS/RGB switch dosn't cut the sound) the Amiga sound is drowned out.
I quite often connect the sound of the Amiga to the stereo amp close by
(great for sound progs). Below is a small schematic diagram of a
switching arrangement where :-
position (A) allows the Amiga sound to the amp and the tuner sound
to the monitor ;
position (B) allows the Amiga sound to the monitor and the tuner
sound to the amp. Simple but effective.
A *---------*--------------> amp L
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Amiga L >----------* |
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B *-------+--------------> monitor L
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A *-------+-------*------> amp R
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Amiga R >----------* | |
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B *---*---+-------+------> monitor R
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A *---- | |
/ # #
Tuner >----------* | |
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B *----------------
Note : # = small signal diode (eg IN914)
Switch = 3 pole 2 position
use shielded cable only
till next time..............Steve Wright
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