Instrument circuit diagnosis method.

Instrumentation circuit maintenance is always an integral part of electronics companies. Because it is only through it that the products that are not qualified will eventually leave the factory. However, maintenance is also the most complex part of the electronics company. Because it not only applies to many electronic professional knowledge, but also needs to have rich field experience sometimes. The following is the experience that henan hui xiang summed up over the years to share with you.

1. Tap the hand pressure method.

It is often encountered when the instrument is running good and bad, this phenomenon is mostly due to poor contact or virtual welding. This can be done with percussion and hand pressure.

The so-called "rap" is on the part of the fault may be produced, through a small rubber ð ¨ +  head or other tap tap the board or components, see if it will cause error or downtime The so-called "hand pressure" is when the fault occurs, the power is turned off and the plug and socket are pressed back with the hand, and then the machine can be turned on to see if it can eliminate the failure. If you find that a knock on the shell is normal, and if the knock is not normal, it is better to put all the joints back in place and try again. If you don't succeed, you will have to do something else.

2. Observation

Use vision, smell, touch. At some point, the damaged components will become discolored, bubbling or charred. Burnt devices produce special odors; Short circuit chips will be hot; Virtual or unsoldered joints can be observed with the naked eye.

3. Elimination.

The so-called elimination method is a method to determine the cause of failure through some plugins and devices in the machine. When the instrument is returned to normal after the removal of a certain board or device, the fault occurs there.

4. Substitution method

Two machines of the same type or sufficient spare parts are required. Replace a good spare part with the same component of the fault machine to see if the fault is eliminated.

5. Comparison method

There are two models of the same type, and one is running normally. Use this method to have the necessary equipment, for example, multimeter, oscilloscope and so on. According to the comparison, voltage comparison, waveform comparison, static impedance comparison, output comparison, current comparison, etc.

The specific method is: let the defective instrument and normal running in the same situation, and then some detection point of signal be comparative test of two groups of signal, and if there is different, you can conclude that fault out here. This method requires the maintenance personnel to have considerable knowledge and skills.

6. Lifting and cooling method

Sometimes, work a long time, or working environment at high temperature in summer can appear fault, check normal shutdown, stop for a period of time it is normal again, fail again in a moment. This phenomenon is due to the poor performance of individual IC or components, and the high temperature characteristic parameters cannot meet the requirements of the index. In order to find out the cause of failure, the method of lifting and cooling can be adopted.

The so-called cooling is when the failure occurs, the use of cotton fiber will be used to wipe off the potential failure of the water, to cool down, to see whether the fault is eliminated. So-called warming is artificially to environmental temperature, such as soldering iron nearer questionable parts (note must not will increase temperature too high, so that damage the normal device) and proved whether the fault appears.

7. Shoulder riding

The shoulder method is also called parallel method. Put a piece of good IC chip in to check the chip, or the good components (resistor capacitor, diode, triode, etc.), and to check the components in parallel, keep good contact, if internal open circuit fault from the device or poor contact, that is the way that can be ruled out.

8. Capacitor bypass.

When a circuit produces a strange phenomenon, such as a display disorder, it can be used to determine the circuit portion of the fault by the capacitive bypass method. Connect the capacitor to the power and ground end of IC; The influence of the fault phenomena on the transistor circuit is observed on the base input or collector output terminals. If the capacitor bypass input end is invalid and the output end of the bypass is lost, the fault is determined in this primary circuit.

9. State adjustment method.

Generally speaking, do not touch the components in the circuit before the failure is determined, especially the adjustable device, such as the potentiometer. However, if the precautionary measures are taken in advance (for example, to make a position marker or to measure the voltage or resistance value before being touched), you may be allowed to be touched if necessary. Maybe sometimes the fault will disappear after the change.

10. Isolation method

The fault isolation method does not require the same type of equipment or spare parts for comparison, and is safe and reliable. According to the fault detection flow chart, the fault search area is gradually narrowed, and the fault location is quickly detected by means of signal comparison and component exchange.