The root cause of IN-AND-OUT electrical failure can be defined as below situations according to probability of proportion:

(1) Poor contact:

Poor contact occurs among the card slot and golden finger of printed circuit board, breakoff happens on cabled twist through the internal barrier, bad contact on wire cord and/or terminals, components lead COLD SOLDERING on the metal pad of printed circuit board;

(2) Signal interference:
For digital circuits, failure will be presented under certain condition, there may indeed be too much interference affecting the control system, but also parameters of the individual component and/or overall performance parameters of circuit board have changed, so that failure occurs result from the  interference ability tends to the critical point.

(3) Thermal stability of parts:
From great amount of repairing practice and experience, electrolytic capacitors present the worst thermal stability, followed by the other capacitor, transistor, diode, IC, resistors, etc.;

(4) Residue on the PCB circuit board:

Moisture, dust and other residue on the surface of printed circuit board are conductive with a resistance effect, this resistance value will also change in the process of thermal expansion and contraction, the resistance value will have parallel effect in conjunction with the other components, the circuit parameters will be changed once the effect become stronger and caused failure occurs.

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