How to fix a multimeter with detached wires and pens
1, multimeter red and black pen in the stake, you can pull out, see a metal male socket connected to a leather wire, just because the junction of this line column is easy to break, tell you, my pen line has been much shorter, repair many times, each time to waste 1cm, I have two kinds of table (electronic, pointer) are unloading the line to repair the pointer table line connector is good to repair some, as long as there is a threaded red plastic on the set of unscrewing the metal stake clamped to a vise, use a soldering iron to melt on the solder wire, and then the leather wire stripped out half a centimetre to reveal the copper wire, melted with tin. In a vise, with a soldering iron melted on the solder wire, and then stripped out half a centimetre of the leather wire, exposing the copper wire, melted with tin, it is best to set an insulating wax tube on the line, so that after soldering outside the casing will not be easy to break.
2, for the digital table stakes are not very good welding, it's a large and hard plastic sleeve, you have to pull out the first line through the line, welded on the outside and then return it to its original position, if you do not even have the welding technology, it would be difficult!
LED lamp driver power supply with a multimeter to measure the output voltage 319V
LED power supply belongs to the constant current drive power supply, output voltage range 125V ~ 140V, output current 360mA ± 3%, power consumption of about 60W. it means that in the voltage range of 125V ~ 140V, the output current is 360mA. 3V/2W LED lamp beads as an example, by 125/3 ≈ 41.7, 140/3 ≈ 46.7 can be seen that the LED drive power supply can be Series connection of 42~47 LED lamp beads.
Why no-load measurement of its voltage value of 319V? According to U = IR can be seen, no matter how much resistance, when the current I = 0, the voltage value is also 0. So constant current source, when the load current is 0 (no load) series current limiting resistor or capacitive resistance bucking and other current limiting circuits and did not step down, the actual measurement of the voltage value of 220V alternating current rectified, filtered DC voltage, 220V rectified and filtered no-load output voltage 220V * 1.414 = 311V, and the utility power supply 2.0V, the voltage value is 319V, the voltage value is 319V. 311V, and the mains 220V will have up and down 5% deviation, so the no-load measurement of 319V is normal. The following figure is a LED constant current drive power supply designed using PT4207 high-voltage step-down LED driver control chip, PT4207 built-in a 350mA switch, and is equipped with an external MOS switch drive port, for the application of 350mA or less do not need external MOS switch, when the drive current is greater than 350mA can be through the expansion of an external MOS tube.
