What about the laptop motherboard power supply?

What to do if the laptop motherboard is out of power:

First step.

First, pin 14 and 15 short, and if the fan on the ATX power supply rotates, skip this step and look at the next one.

If the fan on the ATX power supply does not rotate, use a multimeter to cross the +5svb end of the Pin9 to measure the Pin15 voltage, and if there is a +5v voltage, then there is a doorway, please see the next one. If there is no voltage, generally please discard this power supply, because the difficulty of maintenance is greater. If you want to continue to repair, please look down. +5VSB as long as the ATX power supply board There is a +5VSB standby voltage output, no voltage, is standby to start the power damage, this part of the circuit is a separate small power transformer circuit, similar to a switching power supply of the phone charger circuit.

ATX Switching power supply, the auxiliary power supply circuit is to maintain the computer, ATX power supply can work correctly the key. First, the auxiliary power supply to the microcomputer motherboard power monitoring circuit output +5VSB standby voltage, when the motherboard str standby, this unit circuit is responsible for the motherboard memory power to maintain the information in memory is not lost. Second, to ATX power supply internal pulse width modulation chip main work IC TL494 12 feet and push transformer primary winding to provide DC working voltage +22v. As long as the ATX switching power supply to the mains, whether or not to start the computer, there is +5VSB standby start-up voltage output. The auxiliary power supply circuit is in the working state of high frequency, high voltage self-excited oscillation or controlled oscillation, and the partial circuit lacks the perfect regulation and overcurrent protection, which makes it become the most fault rate in ATX power supply. This paper takes the three domestic ATX switching power supply used in the microcomputer as an example, and analyzes the working principle of the auxiliary circuit in combination with the maintenance example as follows:

First, Galactic Silver Star -280b

ATX Power supply Auxiliary circuit

After rectification of the 300V DC voltage, through the current limiting resistance R72, starting resistor R76, T3 drive transformer primary winding L1 respectively added to the Q15 oscillating tube B, c pole, Q15 conduction. The feedback winding L2 the inductive potential, and the positive feedback loop C44 and R74 add to the q15b pole to accelerate the Q15 conduction. T3 two times winding L3, L4 inductive potential on negative positive, rectifier tube BD5, BD6 cut-off.

With the increase of the C44 charge voltage, the Q15 current of injection is less, Q15 exit saturation and enter the amplification state, the oscillation current of L1 winding decreases, because the current in the inductance coil cannot be changed, the L1 winding inductive potential is reversed, and the reverse phase induction potential of the L2 winding is R70, C41, D41 Loop to the C41 charge, C41 positive electrode grounding, negative cathode potential, so that ZD3, D30 conduction, Q15 base is rapidly pulled to negative potential, Q15 cut-off. T3 two times winding L3, L4 inductive potential on the negative, BD5, BD6 rectifier diode output two DC power supply, which +5VSB is the host wake-up ATX Power controlled start of the operating voltage, if the voltage is abnormal, when the keyboard, mouse, network remote mode to boot or press the chassis Panel Start button, ATX Power supply could not be controlled to start output multi-channel DC power supply.

During the cut-off period, the C44 voltage is discharged by R74 and L2 windings, with the C44 discharge voltage decreasing, the Q15 radical potential picks up again, once more than 0.7v,q15 leads again. During conduction, C41 by R70 discharge, if the C41 discharge circuit time constant is much larger than the Q15 oscillation period, the end of the Q15 base to form a positive guide 0.7V, reverse cut-off negative bias voltage potential, reduce Q15 turn-off loss, D30, ZD3 composition of the base pole negative bias cut-off circuit. R77, C42 as the absorption loop of resistance and capacity, inhibit

A spike resonant pulse produced by absorbing the Q15 cut-off runtimes electrode. The auxiliary power supply without any controlled adjustment voltage protection circuit, common fault is R72, R76 resistance to become large or open, Q15, ZD3, D30, D41 breakdown short-circuit, and with the AC input rectifier filter circuit in the breakdown of the rectifier, the exchange of insurance burst phenomenon. Hidden fault is C41 due to close to Q15 heat sink, heat baking and capacity decline, resulting in two times winding BD6 rectifier output voltage in the ATX power supply instant surge, up to 80V, power instantaneous often burned DBL494 pulse width modulation chip. This fault is quite concealed, amateur overhaul is generally not easy to detect, resulting in a considerable part of the Galactic ATX switching power supply to repair failed to find the source of the fault, and then burned the new components.

Second, Sen da Power98

ATX Power supply Auxiliary circuit

The self-excited oscillation works in the same way as the Galactic ATX switching power supply. The overcurrent adjustment tube Q2 is added in the primary winding oscillation circuit of T3 drive transformer. Q1 self-excited Oscillation is regulated by Q2, when the T3 primary winding rectifier input voltage rises or two times the winding load is overloaded, flows through the L1 winding and the q1c, the e pole oscillation current increases, the R06 overcurrent detection resistance Pressure drop rises, by R03, the R04 passes to the q2b pole, The q2b pole potential is larger than the 0.7v,q2 conduction, the Q1 base potential is pulled down, the Q1 saturation conduction time is shortened, and the energy storage of the primary winding from the electric energy to the magnetism is reduced, and the output voltage of the two windings rectifier decreases. and Q1 oscillation switch autofrettaged oscillation normal, Q2 adjustment tube cut-off. This circuit improves the reliability of auxiliary power supply to some extent, but when the mains is up, the rectifier input voltage rises, or the load of the T3 two windings is too heavy, the Q2 adjustment function lags, it still burns R01, R02, Q1, R06 components, sometimes affecting ZD1, D01, Q2 components.

Third, the technical exhibition

200XAATX Power supply auxiliary circuit, its primary winding edge with the above two kinds of circuit, the secondary winding side increases the overvoltage protection circuit. The working principle is as follows: If T3 two times winding output voltage rises, by R51, R58 partial pressure, precision regulator Q12 reference end your potential rise, control end UK potential drop, IC1 light-emitting diode conduction, photosensitive transistor C, e pole output current flow into the adjustment tube Q17 base pole, The Q17 conduction causes the oscillation switch tube to Q16 the cut-off, thus acts as the Overvoltage protection function. D27, R9, C13 composed of Q16 peak resonant pulse absorption circuit, C29, L10, C32 composed of filter circuit to eliminate the +5VSB ripple voltage.

Step two.

Pin 14 and 15 short, if the ATX power supply fan rotation, indicating a +12v output, may be a large ripple voltage is not normal use. Please turn on the power, carefully observe what the capacitor "foaming", will be replaced can be repaired. Note: Here the capacitance is used +85℃ or 105 ℃ above. Step three.

Pin 14 and 15 short, if the fan on the ATX power supply does not rotate, but the purple Pin9 has a +5vsb voltage on it, indicating that the main switching circuit of the power supply is faulty. The pins 14 and 15 are short, the fan on the power supply does not rotate, and the purple Pin9 has a +5vsb voltage. This type of failure my typical maintenance example:

1). Open the Power box, found that two of the largest electrolytic capacitors have a top of the slurry phenomenon, that is, schematic diagram of the C1 or C2 damage to one, the two capacitors together with the same specifications of the capacitor (withstand pressure of more than 200V capacity larger the better), troubleshooting. The cause of the failure is C1 or C2 arbitrarily damaged one, the main power switch transformer can not form AC current, so it can not power.

2. Open the Power box, found that the internal circuit board looks good, no obvious damage traces, no capacitance foaming phenomenon. Measurement of two main power switch transistor is normal, live measurement C1 and C2 have about 160V voltage, normal. Along the downward inspection found that the capacitor C3 the phenomenon of virtual welding, after reflow power repair. C3 is thick flake polyester capacitor under the action of the external force is prone to shake the phenomenon of virtual welding, it is estimated that in the production of the time has been a slight deficiency welding and welding feet of the lack of tin, and then can show their own virtual welding to be not surprising.

3. Open the Power box, found that the internal circuit board looks good, no obvious damage traces, no capacitance foaming phenomenon, but carefully observe the main power switch transistor, found that there is a slight fissure. After measurement, the damage was found with two MJE13007 or two bu508a (508A easy to buy, color TV power supply tube) will be the original two main power switch three-pole to the tube replacement, according to experience failure should be excluded, but the pin 14 and 15 short is still no +5 and +12v power supply, Not working properly. Limited to the tools on hand only the multimeter has no oscilloscope and other advanced tools, maintenance had to use their brains to carefully analyze the circuit. I don't have the relevant information on hand, only the control circuit board to draw the main circuit diagram, the drawing circuit diagram is the above schematic diagram, and later downloaded the ATX schematic diagram on the internet but there is no this I draw the schematic diagram of the simple and easy to use, so in this specially to use the computer to draw down for everyone. Now +5VSB have, all capacitors are normal, the main power switch transistor has been normal, it seems that the fault should be the main power switch transistor base is not driving signal or drive is not enough. Add electricity and short pin 14 and 15 experiments do not have any movement, power off after the main power switch transistor heat sink or room temperature, so exclude the possibility of the base extremely incentive. The reason for determining the failure is that the base has no drive signal. But the visual main power switch transistor peripheral circuit is completely normal, the main work IC TL494 has been sent to drive the main power switch transistor excitation signal? To the power supply board normal

Electric and short pin 14 and 15 to make the power supply in normal working condition, using the db AC of multimeter, the two hands bridging in the diagram as shown in the drive of the cold end of the AB drive of the b at both ends, the measurement unexpectedly has nearly 10v≈ AC signal. Such a high voltage estimate is caused by the empty load, that is, the main work IC TL494 sent out the driving signal, but not to the main power switch transistor base. It is clear that the current range of failures is reduced to two places: there is a problem with the base-coupled circuit that drives the transformer to damage or is the main power switch transistor. After inspection found that the appearance of good R4, R5 resistance became very large, with 1/8w resistance replacement troubleshooting. The original is the original R4 R5 resistance is 1/16w resistance, power is too small, damage to the appearance of the same as the new resistor, this fault has a certain degree of concealment.

Fourth step.

The special problem solves one example, if has the similar use this legal may rule out: The phenomenon: the Milky Way high quality ATX power supply, when the mains power supply is insufficient, one has the air-conditioner to start the computer to restart. This phenomenon has been bothering me for some time. Their ups can not be used normally: battery power when the CRT monitor was opened by others caused degaussing coil suddenly open recoil high-voltage damage inverter mos tube, Yunxi County everywhere is not equipped with low voltage and high current inverter with MOS tube, had to use small power mos+ high-power transistor complex form repair, There is no problem with the TV and the Monitor, which is to reboot the machine when the computer is transferred to the inverter. It appears that the normal and reverse-switching reaction slows down and causes a reboot.

FIX: A 450V220UF color TV is installed on the circle part of the ATX power supply, fixed to the ATX power supply, and still uses the original UPS to no longer have a similar failure. Add the capacitor to pay attention to the use of authentic licensed, installation attention to polarity, can not be reversed, and the minimum to have 400V of pressure, +85℃ or 105 ℃ temperature, capacity is greater the better.

Fifth step.

The fault in the ATX power supply that I have repaired is generally the failure to respond to pins 14 and 15.50% of the fault is no +5v standby voltage, as long as the standby power of the switch to the +310v between the base to the start of the resistance to replace can be repaired, the resistance is generally around 500k-600k, You can also change the larger point. Standby voltage has no boot is mostly +12v, +5v, +3.3v rectifier tube breakdown, resulting in power protection, there is a capacitor short-circuit broken. In some power supply there are also the main power filter capacitor blowing up, leakage of the fault. I met the basic is such a few types of fault, and then a little more complex to repair the value of, because the purchase of a power supply is only dozens of yuan, it is not worthwhile to spend time and effort.

Sixth step.

ATX Power Maintenance Material (1) main IC TL494 chip function: 12 feet power supply 7-40v;14 foot output +5v

Vref Voltage-stabilizing power supply to protection circuit, PG Circuit, Pson Circuit power supply; 4 feet is Pson low level power supply to open effective joining end, 8 feet and 11 feet is the main power switch transistor base-driven output, in the IC is the transistor's C-polar output. When 4 feet for low power 8 and 11 feet no pulse output indicates TL494 damage.

(2) The voltage is normal, but still can not use the normal computer, this is no PG signal problem, follow this train of thought maintenance on it. This kind of fault is very rare, repair is not difficult, no longer detailed description. PG signal Flow: When power-on, the voltage is normal after the delay of the output +5V PG signal to the motherboard power is ready, your motherboard can now enter the official boot loading process. Power off, a slight decrease in voltage and a little power supply when the PG signal to turn into a low level, tell the motherboard power will be off immediately, you immediately shut down the processing. PG signals are also known as P-OK or POWER_OK signals. To verify that the PG signal is not a problem can be artificially simulated PG signal test can be known. (3) ATX Power supply is characterized by the use of the TL494 chip 4th foot of the "Dead Drive control" function, when the foot voltage for +5v, TL494 9th, 11 feet without output pulses, so that two switch tubes are closed, the power supply is in standby state, no voltage output.

When the 4th foot is 0V, the TL494 has a trigger pulse provided to the switch tube, and the power supply goes into normal working condition. Auxiliary power supply all the way out to send TL494, the other way out through the partial voltage circuit to get "+5VSB" and "ps-on" two signal voltage, they are +5v. Where the "+5VSB" output is connected to the ATX motherboard's "Power Monitoring Unit" as its operating voltage, requiring "+5VSB" output to provide 10mA of operating current. The output of the "Power Monitor part" is connected to "ps-on", when the trigger button switch (unlocked switch) is not pressed, "ps-on" is +5v, it is connected to the positive phase input of the voltage comparator U1, and the voltage of the U1 negative input port is about 4.5V, so the input of the voltage comparator U1 is +5v. The "Death Drive control Foot" sent to TL494, which causes the ATX power supply to be in standby state. When the Power Monitor trigger button switch of the motherboard is pressed (mounted on the panel of the host box), the "ps-on" becomes low, then the output of the voltage comparator U1 is 0V and the ATX host power is turned on. Press the trigger button on the panel again to turn the "ps-on" into a +5v, thus turning off the power. At the same time can also use the program to control the "Power monitoring Parts" output, so that "ps-on" into +5v, automatic shutdown power. If the shutdown command is issued under the Win9x platform, ATX Power is automatically turned off