First, open the pcb design diagram on the computer, light up the short-circuit network, to see where the closest place, the easiest to connect to a piece.Special attention to the short circuit inside the IC.
Two, if it is manual welding, to develop good habits:
1.Before welding, visually check the PCB board, and check the key circuit (especially power supply and ground) with a multimeter;
2. After welding a chip each time, use the multimeter to test a short circuit to power and ground;
3. Do not throw the dering iron when welding. If the solder is thrown on the welding foot of the chip (especially the table paste components), it is not easy to find.
Three, found a short circuit phenomenon.Take a plate to cut the line (especially suitable for single / double plate), energize each functional block and gradually eliminate.
Four, the use of short-circuit positioning analysis instrument, for some conditions in specific circumstances, the use of instruments and equipment detection efficiency is higher, the detection correct rate is higher.
Five. If there is a BGA chip, because all the welding points are covered by the chip, and the multi-layer plate (more than 4 layers), it is best to divide the power supply of each chip in the design, connect with magnetic beads or 0 European resistance, so that the power supply is short to the ground, cut off the magnetic bead detection, it is easy to locate to a certain chip.Due to the difficulty of BGA welding, if not the automatic machine welding, a little attention will short circuit the adjacent power supply to the ground.
Six. Small size gauge paste capacitance must be careful when welding, especially the power supply filter capacitance (103 or 104), which is a large number, and it is easy to cause a short circuit between the power supply and the ground.Of course, sometimes with bad luck, you will encounter the capacitance itself is a short-circuit, so the best way is to test the capacitance first before welding again.
Circuit board maintenance, if the public power short circuit fault often big, because many devices share the same power supply, each with this power device is suspected of short circuit, if the components is not much, using the way of "hoe earth" can find the short circuit point, if the components are too much, "hoe earth" can hoe to the situation will depend on luck.
plug-in capacitance on the circuit board can cut one foot with a diagonal clamp (cut from the center, not root or circuit board cut), plug-in IC can cut the power VCC foot, when a foot short circuit disappeared, a chip or capacitor short circuit.
The IC power pin can be burned on the copper foil thickness is 35um, printed line width 1mm, then every 10mm long, its resistance value is about 5m ω, such a small resistance value, with ordinary multimeter is not measured, with milliohm meter can be measured. Short-circuit, we assume that a certain element with ordinary multimeter is 0 Ω have been measured, measured by milliohm table is probably dozens to hundreds of milliohm milliohm, we will pens and two feet fits in short circuit element measurement, the resistance must be minimum (as if on the other components on two feet measurement, the resistance includes circuit board copper foil line of resistance), So we decided to compare the resistance difference of the milliohm meter, when a component (if it is solder or copper foil short circuit is also the case) to get the smallest resistance, then the component is the key suspect. You can quickly identify obstacles by deciding on them.
