This Video Line Magnifier allows you to view the contents of a certain video line on your oscilloscope. Your scope must have an external trigger input.
For example, you can use it to closely watch a line containing a Macrovision signal. But of course you can also use it for servicing TVs and VCRs.
The video signal is connected to U1,a video sync separator. Pin 7 becomes H when the first line begins. This signal triggers MMV U2A. It's output Q (pin 6) will become H (and not Q, pin 7, becomes L). After a certain time (adjustable with P1), the output states reverse. This will be the trigger signal for the oscilloscope.
Connect the channel 1 input of the oscilloscope directly to the video signal and the trigger input to the TRIG pins. Set the trigger source to 'External'. Turn P1 until the scope shows the line you want to see. Since the scope is triggered just 25 times per second, the picture on an analog scope may be very dim. In that case turn up the Intensity (Brightness) control of the scope.
Instead of a 4528, you may also use the pin-compatible 4098.
Since the Video Line Magnifier has its own voltage regulator (U3), you can use a simple 8...35V/50mA unregulated power supply. Connect the '+' to VPOS and the '-' to VGND. U3 may also be a 78L05. Please note the pin layout:
|1=IN, 2=GND, 3=OUT.||1=OUT, 2=GND, 3=IN.|
You can download the PCB (printed circuit board) of in several formats here: JPEG, EPS and HPGL.
The component layout looks like this:
The 100n caps have 3 pads, so you can use a 5mm (0.2 inch) or a 7.5mm (0.3 inch) type. If you observe the polarity of C4 and the ICs, there's nothing that can go wrong.