teardownit

  General description LRS-75-24 is a 24-volt power supply with a maximum current of 3.2 amperes. According to the manufacturer, the unit operates at a mains voltage of 100 to 240 volts without an additional switch. It has no PFC function. The supply measures approximately 4 × 4 × 1 1/5 inches (99 × 97 × 30 millimeters) and is made on a printed circuit board fixed to the base of the metal case. The top cover is perforated, and the holes are meant for passive cooling. The input and output circuits are connected to a common screw block (1). From right to left, there are 3 terminals for the input line, neutral, and ground wires, and terminals 4 and 5 are the outputs: ground and +24V. The input voltage goes to the fuse and inrush current limiter (2), then to the RF interference filter (3), and finally, to the diode bridge (4). The inrush current limiter has no markings; apparently, it is just an NTC. The rectified mains voltage is supplied to the 150 uF, 400V capacitor (5) and then to the f

Intermittent faults ('floating' defects) are damages that manifest themselves periodically and are caused by poor-quality core connections or reduced insulation resistance. Customer complaints about short-term connection losses are evidence of defects of this kind. Such defects may appear due to mechanical damage to the cable (for example, in the event of vibration from heavy vehicles, rotary equipment, etc., nearby). Typically, when a technician encounters this type of damage, he has to wait patiently for it to manifest itself, hoping the effect will last long enough to determine its location. There is no guarantee that the damage will reveal itself while the technician is on duty. The use of reflectometers allows one to automate this process and maximize productivity. Some reflectometers have a special function for detecting intermittent faults. The device connected to the line accumulates all reflectograms over a certain period and displays them superimposed on each other. W

  Sometimes, a microcontroller does not have enough pins to receive signals from buttons or display them on LED indicators, control relays, etc. Sometimes, one needs to interconnect two digital devices with a single cable, and it would be great to transmit eight, sixteen, or more signals over two to three wires to avoid needing a thick cable. Or, let's say we just want to make a lighting effect for a street sign. One does not need a whole computer or a microcontroller for this task. All these cases (and many others) should be designed with shift registers. As children, many of us had an NES (Nintendo Entertainment System) game console. Its gamepad had 8 buttons: a plus-shaped button for left, right, up, and down, then Select, Start, A, and B. And there were only five wires in the gamepad cable: ground, +5-volt power, and three signal wires. Meaning the state of eight buttons was transmitted over three wires. In the core of the gamepad is a single CD4021 chip. It is an 8-stage paral