What role does the regulated power supply play in repairing mobile phones
How to Repair Computer Motherboard Power Supply
first step.
First short-circuit Pin14 and 15, if the fan on the ATX power supply rotates, please skip this step and see the next one.
If the fan on the ATX power supply does not rotate, please use a multimeter to connect the +5SVB terminal of Pin9 to measure the voltage of Pin15 to ground. If there is a voltage of +5V, then there is a way, please see the next item.
If there is no voltage, generally please discard this power supply, because it is more difficult to repair. If you still want to continue repairing, please read below.
+5VSB As long as there is power supply on the ATX power board, there will be a +5VSB standby start-up voltage output. If there is no voltage, the standby start-up power supply is damaged. This part of the circuit is a separate low-power start-up transformer circuit, similar to a charger circuit for a mobile phone with a switching power supply.
In the ATX switching power supply, the auxiliary power supply circuit is the key to maintain the normal operation of the microcomputer and ATX power supply.
First, the auxiliary power supply outputs +5VSB standby voltage to the mainboard power monitoring circuit of the microcomputer. When the mainboard STR is in standby, this unit circuit is responsible for supplying power to the memory of the mainboard to maintain the information in the memory from being lost.
Second, provide DC working voltage +22V to pin 12 of ICTL494, the main working ICTL494 in the internal pulse width modulation chip of the ATX power supply, and the primary winding of the driving transformer.
As long as the ATX switching power supply is connected to the mains, no matter whether the microcomputer is started or not, there will be +5VSB standby starting voltage output. The auxiliary power supply circuit is in the working state of high-frequency, high-voltage self-excited oscillation or controlled oscillation,
Part of the circuit itself lacks perfect voltage regulation and overcurrent protection, making it the part with the highest failure rate in ATX power supplies
second step.
Short connect Pin14 and 15, if the fan on the ATX power supply rotates, it means that there is +12V output, and it may be that the ripple voltage is relatively large and cannot be used normally. Please turn on the power, carefully observe which capacitors are "foaming", and replace them all to repair them.
Note: The capacitors here are always used at +85°C or above 105°C.
third step.
Short-circuit Pin14 and 15, if the fan on the ATX power supply does not rotate, but there is a voltage of +5VSB on the purple Pin9 to ground, it means that the main switch circuit of the power supply is faulty.
Short-circuit Pin14 and 15, the fan on the power supply does not rotate, and measure the voltage of +5VSB on the purple Pin9 to ground. My typical maintenance examples of this type of failure:
Open the power box and find that the top of the two largest electrolytic capacitors has burst phenomenon, that is, one of C1 or C2 in the schematic circuit diagram is damaged. Replace the two capacitors together with capacitors of the same specification (capacity above 200V withstand voltage) bigger is better), troubleshooting.
The cause of the failure is that either C1 or C2 is damaged at will, and the main power switching transformer cannot form an AC current, so it cannot supply power.
Open the power box, and found that the internal circuit board looks good, no obvious signs of damage, no capacitor foaming. The measurement of the two main power switch transistors is normal, and the live measurement C1 and C2 have a voltage of about 160V, which is normal.
When checking downwards, it is found that the capacitor C3 has a false soldering phenomenon, and the power supply is repaired after re-soldering. C3 is a thick sheet polyester capacitor that tends to shake under the action of external force and cause false soldering. It is estimated that there has been a slight soldering during production and the amount of tin in the soldering leg is insufficient. Later, it can show itself as soldering. No wonder.
Open the power box, and found that the internal circuit board looks good, no obvious signs of damage, no capacitor foaming phenomenon, but carefully observe the main power switch triode, found that there is a slight crack in one elephant.
After measurement, it was found to be damaged. Use two MJE13007 or two BU508A (508A is easy to buy, the power tube used in the color TV power supply) to replace the original two main power switch transistors. According to experience, the fault should be eliminated, but the If Pin14 and 15 are shorted, there is still no +5 and +12V power supply, and it cannot work normally.
the fourth step.
An example of special problem solving, if there is similar use of this law, it can be ruled out: Phenomenon: Galaxy high-quality ATX power supply, when the mains power supply is insufficient, the computer will restart as soon as the air conditioner is turned on.
This phenomenon has bothered me for a while. My own UPS cannot be used normally for the time being: the degaussing coil is suddenly turned on due to the CRT display being turned on by someone else when the battery is powered, and the high voltage damages the inverter MOS tube. It has to be repaired in the composite form of low-power MOS + high-power triode. There is no problem with the TV and monitor, but the machine needs to be restarted when the computer host is transferred to the inverter.
It seems that the slow response when switching between normal and inverter caused the restart.
Repair: Add a 450V220uF color TV capacitor to the circled part of the ATX power supply, and fix it inside the ATX power supply. If the original UPS is still used, there will be no similar failures.
The installed capacitors should pay attention to the use of genuine licensed products, pay attention to the polarity when installing, do not reverse the connection, and must have a minimum voltage of 400V, +85°C or 105°C temperature resistance, the larger the capacity, the better.
the fifth step.
The faults in the ATX power supply I have repaired are generally caused by shorting Pin14 and Pin 15 after the power is connected and there is no response. 50% of the faults are due to no +5V standby voltage, as long as the base of the switch tube of the standby power supply is set to +310V It can be repaired by replacing the starting resistor between them. The resistance value of this resistor is generally around 500K-600K, and it can also be changed to a larger point.
The reason why the battery cannot be turned on with the standby voltage is that the rectifier tubes of +12V, +5V, and +3.3V break down, causing power protection, and some capacitors are short-circuited.
In some power supplies, there are also failures of the main power supply filter capacitor bulging and leakage. The faults I have encountered are basically these types. If it is more complicated, it will not be worth repairing, because it is only a few tens of dollars to buy a power supply, and it is not worth the time and effort to go to it.
