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ATX power supply repair tips
Failure phenomenon, no output measured and found to plug 9 feet No +5 vsb voltage, so you can not judge the work of auxiliary power.
Ic3 l7805 three-terminal regulator measuring inputs and outputs were not voltage, but sometimes there is 20v input voltage, output has 5v voltage, then short the normal voltage output pin 13-14, but then again, the short cable disconnect pass the time nor the output voltage. Auxiliary power collector voltage measurement from the multimeter instructions have been found from vibration, it was suspected that a fault in the transformer secondary winding side。 Replacement capacitor c04, disconnect l7805 input, still no voltage secondary winding, again in accordance with the power failure did not come from the vibration of the end winding from the initial search fails, found that when the switch with a multimeter measuring the collector, the voltage times be back to normal and the enhanced effect by vibration is not to find fault confidence.
Survey found that r02 has become infinite resistance, the role of this resistance is filtered rectified mains voltage into the base switch is open power from the vibration produced a prerequisite, with a 390k resistor to replace r02, troubleshooting .
IC Application Circuit Diagrams way radio equipment, integrated circuits, more and more applications, knowledge of the IC application circuit is a circuit diagram of a key, is one of the difficulties.
1. IC application circuit Application circuit function has the following features:
① It expresses the integrated circuit structure outside the pins, components and other parameters, so that the work of a complete integrated circuit.
② Some IC application circuit, draw a block diagram of the circuit within the integrated circuit, this time on the analysis of IC application circuit is very convenient, but that means little.
③ IC application circuit is a typical application circuit and functional circuit of the former manual can be found in integrated circuits, which appear in the practical circuit, these two little difference between the application circuit, according to this characteristic, in the absence of actual Typical application circuit Application circuit can be used for reference, this method is often used in repair.
④ general expression of IC application circuit unit, a complete circuit, or a circuit system, but in some cases a complete circuit to use two or more integrated circuits.
2. Characteristics of IC application circuit IC application circuit has the following features:
① most of the application circuit does not draw within the circuit block diagram, which is detrimental to knowledge map, especially for beginners to more unfavorable circuit analysis.
② For starters, the application of integrated circuit than the circuit of discrete components is more difficult, which is the internal circuitry of IC do not know the original edge, in fact, in map Ye Hao, repair Ye Hao, integrated circuits more convenient discrete circuit components.
③ on the IC application circuit, the general understanding of the internal circuits and integrated circuits Learn more about the role of the lead case, the knowledge map is more convenient. This is because the circuit has the same type of regularity in their common master, you can easily analyze many different types of integrated circuits with feature application circuit.
3. IC Application Circuit Diagrams methods and attention of IC methods and precautions are mainly the following points:
(1) to understand the role of each pin is the key to understand the knowledge map the role of pin IC application can access the manual。 Know the role of each pin, the analysis of the external circuit pin role of the working principle and components convenience. For example: know the pin is an input pin ①, foot and then the series is the input coupling capacitor circuit, and the circuit is connected to pin ① input circuit.
(2) to understand the role of integrated circuit the pins are three ways to understand the role of IC pins, there are three different ways: First, access to such information; 2 is based on the internal circuit block diagram of integrated circuits; 3 is based on the application of integrated circuit outside of each pin of the circuit characteristics. On the third approach requires a relatively good basis for circuit analysis.
(3) integrated circuit analysis step of the application circuit as follows:
① DC circuit analysis. This step is mainly for power and ground pins outside the circuit. Note: there are multiple power supply pins when the power to distinguish between these, such as whether the former level, after the power supply circuit of pins, or the left and right channel power supply pin; on a number of ground This pin must distinguish. Distinguish between multiple power pins and ground pins on the repair is useful.
② Analysis of signal transmission. This step analyzes the signal input pin and output pin external circuit. When the IC has multiple input and output pins, we should be clear after the previous level, or circuit of output pins; for two-channel circuit also distinguish between left and right channel input and output pins.
③ other pins of the external circuit. For example, to find negative feedback pin, pin, etc. of vibration, this step of the analysis is the most difficult, on the beginner to the role of information by means of pins or internal circuit block diagram.
④ have a certain ability in knowledge map, learn to summarize various features of integrated circuit pin external circuit law, and to master the rules, which enhance the speed of knowledge map is useful.。 For example, the input pins outside the law of the circuit is: through a coupling capacitor or a coupling circuit with the output stage circuit is connected; output pins outside the law of the circuit is: through a coupling circuit and the circuit after the input stage is connected.
⑤ analysis of integrated circuits within the circuit of the signal amplification process, the best access to the internal circuit block diagram of the integrated circuit. Within a block diagram of the circuit when the signal transmission lines through the arrows to know which circuit after the signal amplification or processing, the final signal output from which pin.
⑥ understand some of the key integrated circuit test points, pin DC voltage law on the maintenance of the circuit is very useful.０ｖ。 otl circuit DC voltage output DC voltage equal to half of IC; ocl circuit DC output voltage is equal to 0v; btl circuit DC output voltage of the two are equal, when a single power supply voltage is equal to half the DC, dual power When power is equal to 0v. When the two pins of the IC indirectly resistance, the resistance will affect the two pin on the DC voltage; When the two pins of the coil indirectly, the two pin DC voltage is equal, Unequal coil will be open up; when two pins of a capacitor or indirectly connected rc series circuit, the two pins of the DC voltage is certainly not equal, if the same breakdown shows that the capacitor has been.
⑦ generally not to analyze the integrated circuit within the circuit works, it is quite complex.
1. Blown fuse fault analysis and for this failure, the first turn on the power case, inspection of the fuse blown power supply, whereby the inverter circuit can determine whether the initial failure occurred. c5、c6,ql、q2, If so, the following three conditions are not caused by external: input circuit is a bridge rectifier diode breakdown; high-pressure filter electrolytic capacitor c5, c6 are breakdown; inverter power switch ql, q2 damage.
The main reason is because the DC filter and transform oscillator circuit to work long hours in high pressure (10 300v), high current state, especially because of large changes in AC voltage output when the load heavy, prone to blown fuse fault.。 DC filter circuit consists of four rectifier diodes, two 100kω about limiting resistor and two electrolytic capacitor 330uf about the composition; transform oscillation circuit is mainly installed in the same heat sink on the same two models of high-power switch tube.
AC fuse blows, disconnect the power plug off, the first circuit board carefully observed the appearance of the high-voltage components have been burnt or breakdown traces of electrolyte overflow。 Without exception, with a multimeter measuring the value of the input: If less than 2ookω, shows a partial short circuit back then were measured at two high-power switch e, c resistance among most; if less than 100kω, it indicates switch tube has been damaged, measuring four rectifier diodes are reverse current limiting resistor and the resistance of two, with a multimeter to measure the charge and discharge conditions to determine whether it is normal.。 Also when replacing the switch, if you can not find the same models to choose alternative products, we should pay attention to the collector - emitter reverse breakdown voltage vceo, the maximum allowable collector power dissipation pcm, the collector - base hit reverse through voltage vcbo parameter should be greater than or equal to the original transistor parameters.。 Another to note is that: a component must not be damaged in the identified, direct boot after change, so may still have trouble due to other high voltage components, in turn replace the damaged components.。 Must be on the circuit conduct a comprehensive inspection of all high voltage components measured, the failure to completely rule out the fuse blows.
2. No DC voltage output or voltage output instability if the fuse was intact, in a load case, no output DC voltage levels, the possible reasons are: power appears open, short circuit; over-voltage, over-current protection circuit failure; oscillation circuit did not work; power supply overload; high frequency rectifier diode rectifier filter circuit, the breakdown; filter capacitor leakage, etc..
Processing methods; with a multimeter measuring system board 10 5v power supply to ground resistance, if more than 0.8ω, it indicates the system board without short circuit. The computer configuration to minimize the machine, leaving only the motherboard, power supply, buzzer, measuring the output DC voltage, if still no output, indicating a fault in the computer power supply control circuit。 Controlled mainly by the integrated circuit switching power supply controller (tl-496, gs3424, etc.) and over-voltage protection circuit, the control circuit is working properly is directly related to whether the output DC voltage. Over-voltage protection circuit composed of small-power transistor, or silicon and related components, whether used multimeter measuring the breakdown of the transistor (SCR Zexu welding if measured), the related resistors and capacitors for damage.
3．Power supply output, but no show boot failure may occur due to power good signal input of the reset delay time is not enough, or no power good output.
When turned on, with the voltage meter measured the output power good (then host of a pin power plug), if no +5 v output, then check the delay components; if +5 v output, then change the delay capacitor delay circuit can.
4 Poor power supply load with only the motherboard, floppy drive power when working, when connected to the hard drive, optical drive, or plug in memory, the screen changes from and does not work. The possible reasons are: the transistor operating point is not a good choice, high-voltage filter capacitor leakage or damage, leakage heat regulator diode, rectifier diode failures.
The exchange oscillation circuit transistors to increase the gain, or transfer large transistor operating point. Detected a problem with a multimeter components, the replacement of silicon, zener diodes, high voltage filter capacitor or rectifier diode can be.
1-Today, a Big Dipper repaired power, failure to start the board can not, short access test points, power supply fan will be transferred, amount of voltage output of each group completely normal, but listen to say a word internally, apart found that the filter capacitor 12v bubbling, replacement after work.
2。Recently, repair a colorful (umax) power supply, this is the case, the fault is not power, turn on the power enclosure and found broken glass fuse has instructions within the current large, there is short-circuit point, when I opened the bottom found a small cockroach stick died in boards, and the power of the steel substrate has burned black, the circuit board with melt point circuit board, the first volume of a few power management, good, take a closer, a small cockroach just died in the power supply filter capacitor The 300v both ends, with anhydrous alcohol to clean the circuit board, the measured power input part of the rectifier diodes, four on bad. This is not easy to find the same type of rectifier diodes (this stuff used must be of the same model, or soon will be bad), then a rectifier bridge to find a replacement as usual.
3, lenovo original ps-400atx power, boot no reaction, test +5 vsb is 6.7v, pwon to 3.4v, but the insurance and switch to normal observation center to promote the transformer primary winding circuit of a resistor r11 burned black, the resistance of the Deputy Power Supply +13.8 v supply for the two to promote the transistor c9015 limiting resistor, check similar circuit, the replacement for the 1.5k resistor tl494 color, measuring +5 v reference output 8.4v, the bad block replacement. ＋5vsb+5 Vsb filter capacitor (16v, 470uf) muster, replacement. Vice-power opt coupler in the secondary output current limiting resistor r33 (2.7k) circuit, replace the normal power. Analysis of failure causes for the resistance r33 higher open circuit voltage caused by the Deputy damage caused by a string device.
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