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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 grey red black red brown brown black black red brown red red black brown brown green brown black black brown yellow violet black black brown brown black black black brown violet green black gold brown red yellow black gold brown siliconchip.com.au 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 siliconchip.com.au 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 Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Use this handy form Enclosed is my cheque/money order for $________ or please debit my  Bankcard  Visa    Mastercard Card No: _________________________________ Card Expiry Date ____/____ Signature ________________________ Name ____________________________ Address__________________________ __________________ P/code_______ 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). siliconchip.com.au