Testing knowledge of integrated circuits

- Sep 13, 2017-

1, before testing to understand the integrated circuit and related circuits working principle

Before inspecting and repairing the integrated circuit, we must familiarize myself with the functions of the integrated circuit, the internal circuits, the main electrical parameters, the functions of the pins, the normal voltage of the pins, the working principle of the circuit of the waveform and peripheral components. If the above conditions are met, the analysis and inspection will be much easier.

2, the test does not cause the pin between the short circuit

When testing a waveform with a voltage measurement or oscilloscope probe, the pen or probe does not cause a short-circuit between the integrated circuit pins due to slippage, preferably in a peripheral printed circuit directly connected to the pin. Any instantaneous short circuit can easily damage the integrated circuit, in the test of the flat-type package of CMOS integrated circuits should be doubly cautious.

3, strictly prohibited in the absence of isolation transformers, with the grounding of the test equipment to contact the floor of the electrified TV, audio, video and other equipment

It is strictly forbidden to test the TV, audio and video equipment without power isolating transformer directly with the instrument and equipment which has been grounded. Although the general cassette recorders have power transformers, when exposed to more special output power or the use of the nature of the power of the television or audio equipment is not too familiar with the first to ascertain whether the chassis is charged, or very easy with the floor of the live TV, audio and other equipment caused by short circuit, ripple, the integrated circuit, Cause a further expansion of the fault.

4, should pay attention to the electric iron insulation performance

Do not allow the use of electric iron welding, to make sure that the iron is not charged, it is best to ground the shell of the soldering iron, the MOS circuit should be careful, the use of 6~8v low voltage iron is more secure.

5, to ensure the quality of welding

Welding is indeed a solid, solder stacking, porosity easily caused by virtual welding. Welding time generally does not exceed 3 seconds, the power of soldering iron is applied to the heat type 25W around. The integrated circuit has been welded to carefully check, it is best to use the ohmmeter to measure whether there is a short-circuit between the pins, to confirm that no solder adhesion phenomenon and then connected to the power.

6, do not easily determine the damage of integrated circuits

Do not easily judge that the integrated circuit is damaged. Because the majority of integrated circuits for direct coupling, once a circuit is not normal, may lead to multiple voltage changes, and these changes are not necessarily caused by the damage of the integrated circuit, and in some cases the pin voltage measured with the normal or close, also not necessarily can explain that the integrated circuit is good. Because some soft faults do not cause the change of DC voltage.

7, test instrument internal resistance to be large

When measuring the DC voltage of an integrated circuit pin, a multimeter with a table head internal resistance greater than the 20kω/v should be selected, otherwise there will be a greater measurement error for some pin voltages.

8, should pay attention to the power integrated circuit cooling

The power integrated circuit should be thermally sound, not allowed to work without heat sink in high-power state.

9, the lead should be reasonable

If you need to add the peripheral components to replace the internal circuit of damaged parts, should be selected small components, and wiring should be reasonable to avoid unnecessary parasitic coupling, especially to deal with the audio amplifier integrated circuits and preamplifier circuit between the grounding end.