1. Open bad: (often caused by poor contact with the probe)
In the case of a short circuit group, for example, there is a short circuit group: <1,4,10,12>, ICT test out of 1,10 open circuit, said PCB test point 1 and test point 10 resistance between the greater than 55Ω (or 55-85Ω), you can use a multimeter on the PCB test points to verify; Possible reasons:
1) the test needle is broken, or the needle type is not suitable for the test point on the board to be measured;
2) the test point with rosin and other insulation items;
3) a component missing, poor welding, wrong pieces;
4) the position of the relay, switch or rheostat has changed;
5) Copper foil on the PCB is broken, or between Via Hole and copper foil.
2. Short circuit: (short circuit bad to the first priority, and poor open circuit is often due to poor contact caused by the probe)
Short circuit bad refers to two points (not in the same short circuit group, that should be greater than 25Ω (or 25-55Ω)) resistance is less than 5Ω (or 5-15Ω), you can use a multimeter on the PCB test points to verify; the reason:
1) with welding (should be found in the two NET-related welding points);
2) wrong pieces, multi-loaded devices;
3) the position of the relay, switch or rheostat has changed;
4) test pin contact with other devices;
5) short circuit between copper foil on PCB;
3. Poor components:
Test value deviation tolerance is relatively small, the possible reasons:
1) the deviation of the device itself is so big;
2) the contact resistance of the test needle is large;
3) wrong pieces, poor welding, anti-installed;
Test value deviation tolerance is relatively large, the possible reasons:
1) device is broken;
2) test needle is broken (with the pin connected devices are relatively large difference)
3) the test points are rosin and other insulation items;
4) Copper foil on the PCB is broken, or between Via Hole and copper foil.
5) wrong pieces, missing pieces, anti-installed;
6) poor device welding;
4. IC poor welding (tested with T est J et):
Test value is too small, possible reasons:
1) IC of this foot empty welding;
2) poor contact with test leads;
3) From test point to IC pin Open.
4) IC internal weakness (rarely);
Test value is too large, possible reasons:
1) short circuit phenomenon;
2) IC internal weakness (rarely).
other:
When the R, L test value deviation is 99.99%, D, Q test value is about 2V and the capacitance test value is 0, and several devices have the same test pin, the possible reason: the test pin is broken, or Poor contact with the test point, or broken copper foil on the PCB, or between Via Hole and copper foil. ;
L short circuit and IC wrong pieces, anti-installed will cause large tracts of bad, should give priority to inspection.
L When using the multimeter for inspection, place the multimeter's needle at the test point, not at both ends of the device.
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