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Dr Video Mk.2
An Even Better Video Stabiliser
By JIM ROWE
A
S YOU’RE NO DOUBT aware, a lot
of pre-recorded video software is
now “copy protected”, to stop people
from making their own pirate copies.
In principle, that’s fair enough; having spent millions of dollars making
a movie, the producers are entitled to
get a fair return on their investment.
What complicates the situation is
that the system used to prevent copying involves adding extra pulses to
the normal video signal, some of them
varying in amplitude or “dancing”.
Unfortunately, this prevents quite
a few TV sets and projectors from
displaying a steady picture during
legitimate viewing.
In particular, the extra pulses can
cause problems with large-screen TVs
that display the picture at 100 fields
per second (100Hz) to reduce flicker,
24 Silicon Chip
and also with projectors that perform
line and pixel doubling to improve
picture clarity. They can cause problems with older TV sets, too.
If you have one of these sets or projectors, the only way to get a steady
picture is to somehow remove these
extra pulses. The idea is to “clean
up” the video and let the set’s sync
circuitry do its normal job without
interference. And that’s exactly what
the original Dr Video project described
in the April 2001 issue of SILICON CHIP
was designed to do.
This improved version of Dr Video
removes more of the copy protection pulses than the original design,
for even more stable viewing. It also
handles higher quality S-video signals,
in addition to the normal composite
video handled by the original stabi-
liser. Finally, it also provides a wider
video signal bandwidth, so your pictures won’t suffer any degradation.
Dr Video Mk2 is housed in the same
compact low-profile instrument box
as its predecessor and runs from a
9V AC plugpack supply. As before,
you should also be able to build it for
considerably less than commercial
stabilisers.
How it works
Before we look at the circuit diagram, it may help to explain a little
about the copy protection pulses we’re
trying to remove. We’ll be talking here
about the pulses added to video signals
in the Macrovision copy protection
system, as this is the one most commonly used.
To thwart illegal recording, the
siliconchip.com.au
Do the pictures on your TV set or video projector jitter and
jump around when you’re trying to watch a video movie or
DVD? If so, it’s probably caused by hidden Macrovision signals
that are added to a lot of pre-recorded video software, to
prevent illegal copying. Here’s an improved version of our very
popular Dr Video stabiliser design, which cleans up the video
even more thoroughly for stable viewing. It now also handles
S-video as well as composite video.
Macrovision system adds three main
sets of pulses into the video signal –
two of them essentially combined.
First there’s the “dancing” pulses,
which are added to as many as 14 of
the normally black lines which follow
the vertical sync pulse block, in the
vertical blanking interval (VBI). This
is a group of lines that correspond to
the vertical retrace time, when the
scanning electron beam in the picture
tube is being returned from the bottom
of the screen back to the top, to begin
the next video field.
To each of these 14 or so VBI lines,
the Macrovision system adds as many
as seven extra fake horizontal sync
pulses, each of which is immediately
followed by a short fake video bar
pulse – which can have an amplitude
anywhere between black and peak
siliconchip.com.au
white. It’s these fake video bar pulses
which slowly vary up and down in
amplitude (or “dance”), usually in two
or three groups.
The top traces in Fig.1(a) & Fig.1(b)
show the basic idea. Fig.1(a) shows
the Macrovision signal “dancing”
pulses that are added following the
vertical sync block. These pulses are
constantly changing in amplitude.
Similarly, Fig.1(b) shows the dancing pulses following the colour burst
signal. Note that the lower trace shows
these pulses completely deleted.
In theory, these VBI pulses shouldn’t
upset the operation of the sync separator circuit in a TV or projector – but
they are intended to play havoc with
the sync locking servo and recording
level AGC circuitry of a video recorder.
In particular, the extra sync pulses
should muck up the sync locking,
while the dancing video bars should
fool the recorder’s AGC circuitry into
Where To Buy The Parts
Jaycar Electronics has sponsored the development of this design and they
own the design copyright. A full kit of parts will be available from Jaycar, Cat.
KC-5390. This kit includes a plated-through, solder-masked PC board; all
on-board parts; a case with pre-punched front and rear panels with screened lettering; and a 9V AC plugpack supply.
June 2004 25
Parts List
1 PC board, code 02106041,
117 x 102mm (double-sided –
see text)
1 low-profile plastic instrument
case, 141 x 111 x 35mm
2 RCA sockets, 90° PC mounting (CON1,3)
2 4 pin mini-DIN sockets, PC
mounting (CON2,4)
1 2.5mm LV power connector,
90° PC mounting (CON5)
2 M3 x 10mm machine screws,
with M3 nuts
4 small self-tapping screws,
6mm long
1 100µH RF inductor (RFC1)
Semiconductors
2 MAX4451ESA dual video
op amps (IC1,IC10)
1 74HC4066 quad analog switch
(IC2)
3 74HC00 quad NAND gates
(IC3,IC6,IC9)
1 LM1881 sync separator (IC4)
1 74HC14 hex Schmitt inverter
(IC5)
1 4040B 12-stage counter
(IC7)
1 74HC138 decoder (IC8)
1 7805 +5V regulator (REG1)
1 7905 -5V regulator (REG2)
1 3mm LED, green (LED1)
5 1N4148 signal diodes
(D1-D5)
2 1N4004 power diodes
(D6,D7)
Capacitors
2 2200µF 16V RB electrolytic
2 100µF 10V RB electrolytic
2 2.2µF TAG tantalum
1 220nF MKT polyester
2 100nF MKT polyester
11 100nF multilayer monolithic
1 12nF MKT polyester
1 8.2nF MKT polyester
1 680pF disc ceramic
1 470pF disc ceramic
1 390pF disc ceramic
1 270pF disc ceramic
1 220pF disc ceramic
2 47pF NPO ceramic
Resistors (0.25W, 1%)
1 680kΩ
4 510Ω
1 100kΩ
1 470Ω
1 82kΩ
3 100Ω
2 10kΩ
4 75Ω
2 2.2kΩ
2 24Ω
26 Silicon Chip
varying the recording gain up and
down. All of which they indeed do –
but unfortunately the havoc isn’t just
restricted to VCRs!
EOF pulses
The remaining set of pulses that are
added into the video signals are the
so-called “EOF” or end-of-field pulses.
These are a set of narrow positive
pulses added to the start of about six
lines at the very bottom of the picture
and timed to coincide with the colour
synchronising bursts (ie, immediately
after the horizontal sync pulses).
In effect, these pulses push the
colour bursts for these lines right up
into the peak white region, so the black
level and colour locking circuits of a
VCR are again tricked. Fig.1(c) and
Fig.1(d) show what the EOF pulses
look like on an oscilloscope.
The EOF pulses are harder to remove than the fake sync and dancingvideo-bar pulses in the VBI group. In
fact, we didn’t even try to remove them
with the original Dr Video project.
However we have now worked out a
way to remove them, so this new version of the project removes them as
well as the VBI pulses. This should
provide even more stable viewing.
Now let’s see how it’s done.
Circuit description
Refer now to Fig.3 for the circuit
details. It’s fairly straightforward and
is based on 10 low-cost ICs.
As shown, the incoming video
signal is fed to either input socket
CON1 (composite video) or CON2 (Svideo), with the S-video luminance
component (Y) then going from pin 3
of CON2 to CON1. The chrominance
(C) signal on pin 4 of the S-video socket
is then terminated with a 75Ω resistor
to give the correct loading, as is the
luminance/composite video signal
on CON1.
From there, the S-video signals are
fed into the non-inverting inputs of
IC1a and IC1b, the two wideband op
amps inside a MAX4451ESA dual
video amplifier IC. Note that although
the S-video chrominance (C) signal
isn’t actually processed by the “filtering” circuitry of the stabiliser (it
doesn’t need this), it must be passed
through a matching amplifier stage
to ensure it stays in phase with the
luminance (Y) signal.
Alternatively, if the input signal is
composite video, it is simply fed to
the input of IC1a and IC1b plays no
active role; ie, there is no separate
chrominance signal).
Both IC1a and IC1b are connected as
voltage followers with a gain of one,
so replicas of the incoming signals appear at their outputs (pins 1 & 7). We’ll
ignore the chrominance (C) signal for
the time being, because it is simply fed
to an output buffer amplifier (IC10b)
without any changes. Instead, we’ll
concentrate on the composite/Y signal,
which is now fed in three different
directions from pin 1 of IC1a.
First, the video signal is fed via a
100Ω resistor and series 100nF capacitor to the input of IC4, which is
an LM1881 sync separator. The 100Ω
series resistor is included simply for
decoupling, while the 100nF capacitor
blocks the DC component. A 680kΩ
and a 100nF capacitor from pin 6 of
IC4 to ground set the chip’s internal
timing circuitry for the most accurate
and stable sync separation.
The LM1881 provides a number
of outputs but we only need three of
them. From pin 1, we get a negativegoing composite sync signal, while
from pin 3 we get similarly negativegoing vertical sync pulses (about 230µs
wide). Finally, from pin 5, we get narrow pulses (again negative-going) that
are timed to correspond with the video
signal’s colour subcarrier bursts – ie,
“burst gating” pulses.
IC5d and IC5e invert the latter two
pulse trains, to convert them into
positive-going form. They are then
passed through separate differentiator
circuits, to obtain narrow negativegoing pulses from their trailing edges
– ie, the vertical sync pulses are differentiated using a 390pF capacitor,
10kΩ resistor and diode D2, while the
colour gating pulses are differentiated
by a 270pF capacitor, 2.2kΩ resistor
and diode D3.
These narrow pulses are then used
to trigger simple non-retriggerable
monostable or “one-shot” circuits, to
produce longer pulses of fixed length.
These each consist of a flipflop formed
by two cross-coupled NAND gate elements, plus an RC timing circuit and
a Schmitt inverter.
The monostable formed by IC6b,
IC6c and IC5b is used to produce a
pulse about 1.1ms long, starting at
the end of the vertical sync pulse
from IC4. The end of the output pulse
corresponds closely with the end of
the VBI, so it therefore “covers” all of
siliconchip.com.au
Fig.1(a)
Fig.1(b)
Fig.1(c)
Fig.1(d)
Fig.1: these four scope shots show the action of Dr Video
Mk2 on Macrovision anti-copying signals from a typical
DVD. In each case, the Macrovision signal is the top trace
(blue) while the lower trace (yellow) is the cleaned-up
(doctored) signal. Also in each case, the top trace is taken
from the input at pin 5 of IC1b while the lower trace is the
output at CON3, with a 75Ω terminating plug connected.
Fig.1(a) shows the Macrovision signal “dancing” pulses
that are added following the vertical sync block. These
the VBI lines which should ideally be
black but can have added Macrovision
nasties.
Second monostable
The second monostable is formed
by IC6a, IC6d & IC5a. It is used to
produce a much shorter pulse, about
50µs long, starting at the end of each
colour burst gating pulse from IC4.
This monostable’s output pulse therefore lasts for most of the “active” part
of each horizontal line and certainly
siliconchip.com.au
pulses are constantly changing in amplitude. Fig.1(b)
shows the dancing pulses following the colour burst
signal. Note that the lower trace shows these pulses completely deleted. Fig.1(c) shows the end-of-file (EOF) positive pulses added to the video line signal at the bottom
of the picture. Our circuit drastically differentiates these
pulses so they are much shorter. Finally, Fig.1(d) shows
the expanded EOF positive pulse on the top trace and the
much abbreviated pulse (<200ns) on the lower trace.
covers that part of the VBI lines where
the “dancing” pulses and fake sync
pulses occur.
The output of the upper monostable
(pin 6 of IC6b) is then fed to IC3a and
gated with an inverted version of the
vertical sync pulse from pin 3 of IC4.
IC3a in turn drives inverter IC5c – ie,
IC3a and IC5c together form a positivelogic AND gate.
This gating is necessary because
the LM1881 can itself be disturbed
by the Macrovision pulses, which oc-
casionally cause its vertical sync pulse
output from pin 3 to begin early. This,
in turn, can cause the monostable to
trigger early but the gating ensures that
if this occurs, the monostable’s output
pulse is “blocked” until the end of the
vertical sync block.
The output from IC5c is a pulse
which is high for all of the lines
between the end of the vertical sync
pulse and the end of the VBI. This is
then gated with the 50µs pulses from
the lower monostable using IC3b. As
June 2004 27
28 Silicon Chip
siliconchip.com.au
Fig.2: this is the circuit diagram for
the Dr Video Mk.2, minus the power
supply. Sync separator IC4 and its
associated circuits based on IC5-IC9
generate gating signals which operate
CMOS switches IC2a & IC2c/d. These
switches then strip off any extra sync
and dancing pulses on the vertical
blanking interval lines, along with
the end of field (EOF) pulses, to give a
cleaned-up video signal.
a result, IC3b’s output goes low for
the active part of each line between
the end of the vertical sync pulse
and the end of the VBI but only for
those lines.
This signal is called “VBI GATINGbar” on the circuit and is fed to the pin
4 input of gate IC9b.
We’ll get back to these pulses
shortly. For the moment, let’s turn
our attention to gate IC3d. As shown,
one input of this gate (pin 13) receives
positive-going burst gating pulses from
IC5e, while the other input (pin 12)
receives negative-going 50µs pulses
from the output of IC6d, in the lower
monostable. What’s the idea of this
gating?
Again, it’s needed because of the
way the operation of the LM1881 can
itself be upset by the Macrovision
pulses. In this case, extra burst gating
output pulses can be produced during
the active part of the VBI lines, at some
points in the “dancing pulses” cycle.
By using IC3d to gate the burst pulses
with the complementary output of the
50µs monostable, we make sure that
these unwanted extra pulses are gated
out. As a result, the output of IC3d goes
low only for the 2.4µs duration of the
real colour bursts.
These pulses are labelled “CLEANED
BG-bar PULSES” on the circuit and
drive inverter IC5f. This then turns on
CMOS analog switch IC2b during the
colour burst period of every video line.
And when IC2b turns on, it allows the
following 220nF capacitor to charge
via a 2.2kΩ series resistor, to the current average value of the composite or
Y video signal from IC1a.
Black level
What’s the idea of this? Well, by convention, the average value of a video
signal during the colour bursts is used
to establish the signal’s black/blanking level. So, by turning IC2b on only
during the burst periods, we ensure
that the 220nF capacitor charges to a
siliconchip.com.au
June 2004 29
first 2.5µs just after the horizontal
sync pulses. That’s why this signal
line is labelled “EOF GATING-bar”
on the circuit.
This signal is fed to the pin 5 input of
IC9b, which is used here as a low-input
OR gate. We’ve seen earlier that the
pin 4 input of this gate is fed with the
VBI GATING-bar signals. This means
that the output (pin 6) of IC9b will go
high only at the exact times needed to
remove the Macrovision pulses from
the video signal – either the dancing
pulses and fake sync pulses during the
VBI period, or the narrow pulses at
the start of the EOF lines in each field.
The last step
Fig.3: the power supply circuit uses half-wave rectifiers D6 & D7 to drive
3-terminal regulators REG1 & REG2. These in turn produce +5V and -5V
supply rails to power the Dr Video Mk2 circuit.
voltage which corresponds closely to
the video signal’s black level.
Removing EOF pulses
All of the circuitry we have been
discussing so far is almost identical to
that used in the first Dr Video project.
Let’s look now at the circuitry around
IC7, IC8 and IC9, because this is the
section that has been added to the
new design – to remove those pesky
EOF pulses.
Because these pulses only occur on
the last few lines of each TV field, removing them involves the use of a line
counting system. The actual counting
is done by IC7, a 4040B 12-stage CMOS
binary counter. This is driven by the
negative-going “cleaned” BG-bar
pulses from IC3d at its CLK-bar input
(pin 10), so that its count increments
once for each TV line.
IC7 is reset by the positive-going
vertical sync pulses from IC5d. These
pulses are applied to its MR (master
reset) input at pin 11, so the counter
restarts from zero at the beginning of
each new TV field.
IC8 is a 74HC138 3-to-8 line CMOS
decoder and is used to detect when
IC7 has counted 304 lines in each field
(ie, about eight lines from the bottom).
As well as using the A0-A3 inputs
on IC8, this circuit also uses its three
additional “enable” inputs to provide
what is essentially 6-bit decoding. As
a result, the Y7-bar output (pin 7) of
IC8 goes low only after IC7 has counted
304 lines.
30 Silicon Chip
This pulse is then used to set a
simple RS flipflop made up of crosscoupled NAND gates IC9a & IC9d. This
means that the pin 11 output of IC9d
only goes high on line 305 of each field,
where the “active” part of the field has
finished and where the EOF pulses are
just about to begin.
The other input of the RS flipflop
is pin 1 of IC9a, which is fed with
negative-going vertical sync pulses
from pin 3 of IC4. This resets the
flipflop at the start of each TV field,
taking IC9d’s pin 11 output low again
at the same time.
The result of all this activity is that
pin 11 of IC9d goes high at the beginning of line 305 in each TV field, and
then low again at the very end of that
field and the beginning of the next. It
therefore provides our primary gating
signal for removing the Macrovision
EOF pulses.
IC9c is used to generate the final
EOF gating pulses. It does this by
gating the signal from pin 11 of IC9d
with a differentiated CS-bar output
signal from pin 1 of IC4. In this case,
the differentiator circuit uses a 680pF
capacitor, a 10kΩ resistor and diode
D1.
The differentiated CS-bar signal
consists of narrow (about 2.5µs wide)
pulses which begin immediately after
the trailing edge of each horizontal
sync pulse, so they “cover” the Macrovision EOF pulses. As a result, the
output of IC9c pulses low only during
the EOF lines and then only for the
OK, at this point, we have the 220nF
capacitor below IC2b providing a black
level voltage, plus some positive-going
pulses from IC9b which correspond
to the very times when we want to
remove VBI and EOF nasties. The final
step in cleaning up the video signal is
to put these pulses to work.
As shown, the pulses from IC9b are
fed directly to the gate of analog switch
IC2a. This switch in turn connects the
220nF blanking capacitor and pins 8
& 11 of switches IC2c & IC2d.
In operation, IC2a is turned on during the critical times for the VBI and
EOF lines but left off at all other times.
At the same time, IC3c is used to invert
the gating pulses from IC9b. It’s output
in turn is applied to the gates (pins 6
& 12) of IC2c & IC2d, which are connected in series with the composite/Y
video output from IC1a.
The end result is that during any of
the VBI or EOF gating pulses, IC2c &
IC2d are turned off to block the video,
while IC2a is turned on instead to
clamp the video output to black level.
Still with us? Essentially, all of the
circuitry around IC3, IC4, IC5, IC6, IC7,
IC8 & IC9 is used to produce some fast
gating signals which operate switches
IC2a, IC2c & IC2d. These then “strip
off” any extra sync and dancing video
pulses present on the VBI lines, along
with any spurious spikes on the EOF
lines, and turn these line sections back
into innocuous black. So at the junction of pins 1, 8 & 11 of IC2 we get a
“cleaned up” video signal.
Output amplifiers
The “cleaned” video signal is fed to
buffer amplifier stage IC10a via a 100Ω
resistor. This stage operates with a
gain of two and, like the input amplisiliconchip.com.au
fiers, is part of an MAX4451ESA dual
wideband video amplifier IC.
The output from IC10a appears at
pin 1 and in the case of a composite
video signal, is fed to output socket
CON3 via a 75Ω back-terminating
resistor. Alternatively, for an S-video
signal, the luminance (Y) signal is fed
to pin 3 of CON4 (the S-video output
socket), again via the back-terminating
resistor.
Similarly, for S-video signals, the
chrominance component is buffered
and amplified by IC10b, before being
fed to pin 4 of CON4.
The 100Ω resistor and shunt 47pF
capacitor at the input of IC10a are there
to filter out any transients caused by
the switching of IC2a and IC2c/d. An
identical RC network at the input of
IC10b is included simply to provide
a matching time delay, so the colour
information remains in sync with the
luminance.
Each output buffer amplifier operates with a gain of 2, to compensate
for the 6dB loss caused by the 75Ω
back-terminating resistor in series
with each output (for cable matching).
This gain is set by two 510Ω negative
feedback resistors in each of the output
amplifier stages.
Power supply
Fig.4: install the parts on the top of the PC board as shown here. The red dots
indicate where component leads and “pin-throughs” have to be soldered on both
sides, if you don’t have a board with plated-through holes (top copper shown
above; bottom copper shown below).
Fig.3 shows the power supply circuit. It’s run from a 9V AC plugpack
and uses two half-wave rectifiers (D6 &
D7) to produce unregulated ±12V rails.
These rails are filtered using 2200µF
electrolytic capacitors and fed to regulators REG1 and REG 2 which provide
+5V and -5V rails, respectively.
The output from each regulator is
further filtered using a 100µF capacitor, while the +5V rail also drives LED1
via a 470Ω resistor for power indication. The sync separator (IC4) and all
the logic ICs are powered from the +5V
rail, while the input and output video
amplifiers run from ±5V.
Construction
Building the Dr Video Mk2 project
is very easy, because all the parts
(including the sockets) are mounted
on a single PC board coded 02106041
(117 x 102mm). Once completed, this
board fits snugly inside a standard lowprofile instrument case measuring just
141 x 111 x 35mm.
The front panel is even less intimidating than before, since there are no
controls at all – just the Power LED to
siliconchip.com.au
June 2004 31
Fig.5: the two MAX4451 dual op amps (IC1 & IC10)
are soldered to the underside of the PC board as
shown here. Make sure you install them the correct
way around.
indicate when the stabiliser is operating. The rear panel provides access
to the composite video and S-video
input and output sockets, plus the 9V
AC input connector. There’s no offboard wiring at all – it’s just a matter
of soldering the parts to the PC board.
Note that the PC board is doublesided, as the circuit requires a groundplane. However, unless the board is
supplied with plated-through holes,
you will need to fit short wire “feedthroughs” at various locations on the
board, to connect the copper pads on
each side. You’ll also have to solder
some of the leads of quite a few ICs
and other components to both sides
of the PC board or, in some cases, to
the top copper only.
To make this easy, all the wire feedthroughs and “top solder” points are
marked with a red dot on the parts
layout diagram – see Fig.3.
Note: if you buy a complete kit of
parts from Jaycar, the PC board supplied will have plated-through holes.
This means that you don’t have to fit
the wire feed-throughs and that you
only have to solder the component
leads to the bottom copper pattern.
If your board doesn’t have platedthrough holes, begin the assembly by
fitting all the wire feed-throughs so you
don’t forget them. You can use tinned
copper wire or resistor lead offcuts
for these. Just make sure that they’re
soldered to the copper on each side
of the board.
That done, install the resistors and
the small capacitors, followed by the
diodes and electrolytic capacitors.
Take care to ensure that the diodes and
electrolytics go in with the correct polarity. Table 1 shows the resistor colour
codes but it’s also a good idea to check
each value using a digital multimeter,
before installing it on the PC board.
Don’t forget to solder component
leads to both side of the PC board (or
to the top only if there’s no pad underneath), as indicated by the red dots.
pins of each IC to the board
pads before the rest of
the pins.
Again, don’t forget
to solder the IC pins on
both sides of the board,
if this is indicated by a
red dot on the parts layout
diagram.
Next, install the two 3-terminal
regulators (REG1 & REG2). This involves bending their leads at right
angles so that they lie flat against the
Table 2: Capacitor Codes
Value
220nF
100nF
12nF
8.2nF
680pF
470pF
390pF
270pF
220pF
47pF
Fitting the ICs
The next step involves fitting the
ICs, again taking care with their polarity. As usual, be careful to minimise
the risk of ESD (electrostatic discharge)
damage when handling and fitting the
CMOS devices – ie, use an earthed
iron and solder the supply and ground
μF Code EIA Code IEC Code
0.22µF
224
220n
0.1µF
104
100n
.012µF
123
12n
.0082µF 822
8n2
–
681
680p
–
471
470p
–
391
390p
–
271
270p
–
221
220p
–
47
47p
Table 1: Resistor Colour Codes
o
o
o
o
o
o
o
o
o
o
o
No.
1
1
1
2
2
4
1
3
4
2
32 Silicon Chip
Value
680kΩ
100kΩ
82kΩ
10kΩ
2.2kΩ
510Ω
470Ω
100Ω
75Ω
24Ω
4-Band Code (1%)
blue grey yellow brown
brown black yellow brown
grey red orange brown
brown black orange brown
red red red brown
green brown brown brown
yellow violet brown brown
brown black brown brown
violet green black brown
red yellow black brown
5-Band Code (1%)
blue grey black orange brown
brown black black orange brown
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Silicon Chip
Binders
REAL
VALUE
AT
$12.95
PLUS P
&
P
These binders will protect your
copies of S ILICON CHIP. They
feature heavy-board covers & are
made from a dis
tinctive 2-tone
green vinyl. They hold up to 14
issues & will look great on your
bookshelf.
H 80mm internal width
H SILICON CHIP logo printed in
gold-coloured lettering on spine
& cover
All the parts mount
directly on the PC board,
so there’s no external wiring.
(Note: the final version differs slightly
from the prototype board shown here.
H Buy five and get them postage
free!
Price: $A12.95 plus $A5.50 p&p.
Available only in Australia.
PC board, as shown. Secure their metal
tabs to the PC board using 10mm-long
M3 machine screws and nuts before
soldering their leads.
This mounting method provides a
small amount of heatsinking for the
two regulators but this is mainly necessary for REG1 (7805), as this device
does get warm in operation. By contrast, the 7905 (REG2) runs virtually
cold but securing it in this manner is
still a good idea.
The power LED (LED1) can be soldered in position with its leads straight
initially, leaving about 15mm between
the LED body and the board. Its leads
are then bent forward by 90° about
7.5mm up from the board, so that the
LED’s body will later line up with its
hole in the front panel.
Next, install the 9V AC input connector (CON5) and the two RCA sockets (CON1 and CON3). If necessary,
their holes can be enlarged slightly
using a jeweller’s needle file, so that
the connector lugs all fit correctly.
Make sure the connectors are bedded
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down squarely against the top of the
PC board before soldering their lugs to
the board pads underneath.
Follow these with the two mini-DIN
sockets for the S-video connections
(CON2 and CON4). Again, make sure
that they are seated correctly against
the board before soldering their pins.
Surface-mount ICs
The final step in the board assembly
involves fitting the two MAX4451ESA
surface-mount ICs (IC1 and IC10).
These are in an 8-pin “small-outline”
or SOIC-8 package, which is capable
of being soldered in place manually
– provided you’re careful and use a
soldering iron with a fine-pointed tip.
Both these ICs mount on the underside of the PC board, as shown in Fig.4.
In each case, the IC is installed with
its chamfered side towards the front
of the board (ie, towards the bottom
of Fig.4).
Because their leads are only 1.25mm
apart, you have to be careful not to create accidental solder bridges between
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June 2004 33
The rear panel provides access to the S-video and
RCA sockets for the video input and output signals.
In addition, there’s a power socket to accept the
plug from a 9V AC plugpack supply.
them during soldering. It’s also necessary to solder each lead quickly, so you
don’t damage the IC by overheating!
The best way to approach the job
is to first lightly tin the IC pads, then
tack solder one of the leads to hold
the device in position. The remaining
leads can then all be carefully soldered
and the first lead re-soldered to make
the connection permanent.
Final assembly
The front and rear panels for this
project will probably be supplied
pre-punched, with screened lettering.
These panels can now be fitted to the
finished PC board and the entire assembly lowered into the bottom half
of the case.
The panels slide into the moulded
case slots, while the board is secured
using four 6mm-long self-tapping
screws which mate with matching
plastic spigots in the base (one at each
corner).
Your Dr Video Mk2 is now ready for
its final check out.
Check-out time
There’s no actual setting-up required for this design. However, it’s
a good idea to check that the power
supply is working correctly before
fitting the top cover and putting the
34 Silicon Chip
unit to work in your system.
First, apply 9V AC to the power
input (CON5) from a suitable plugpack. The power LED should light,
indicating that the +5V line is present.
If it doesn’t, remove the power immediately and investigate because you
have a problem.
The most likely cause of a “dead”
LED is that you’ve installed LED1 with
reversed polarity. Check this and if
necessary, remove the LED and refit
it the correct way around.
If the LED is already the correct way
around, then you have a more serious
problem. One possibility is that the
two regulators have been accidentally
swapped over, so make sure that the
7805 is in the REG1 position and that
the 7905 is in the REG2 position.
Neither will work correctly in the
other position and they may even be
damaged if they have been swapped.
The only other likely cause of
power supply problems (and a nonfunctioning unit) is that one or more
of the electrolytic capacitors have been
fitted with reversed polarity. Check
the polarity of the two 2200µF electrolytics, the two smaller 100µF units
and the two 2.2µF tantalum capacitors.
Assuming that LED1 does light,
check the +5V and -5V supply rails
using your multimeter. Both rails
should be within a few tens of millivolts of their nominal values. If so,
your Dr Video Mk2 is probably working correctly and should be ready for
business.
Problems & cures
There are only two possible problems that we can envisage, neither
of them very likely. One is that if the
timing components on pin 3 of IC5b
(in the VBI monostable) are all excessively high in value, you may see a few
black lines at the extreme top of the
picture – and then only with movies in
full screen (4 x 3) format, as opposed
to widescreen/letterbox.
If this happens, it can easily be fixed
by reducing the value of the 8.2nF
capacitor – eg, to 6.8nF.
The other slight possibility is that
the same component tolerance problem might occur in the timing circuit
for the burst gate monostable – ie, at
the input of IC5a. In this case, the
pulses from this monostable might be
lengthened just enough for switches
IC2a & IC2c/d to damage the horizontal
sync pulses – causing horizontal jitter
or tearing.
This is very unlikely to happen but
if it does, the remedy is to replace the
220pF capacitor with a lower value
SC
(say 180pF).
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