【 Weak current college 】 computer regulated power supply common troubleshooting

Overhaul of the ATX power supply, and from PS-ON PW-OK, + 5VSB signal strength. Offline live testing ATX power standby, + 5VSB, PS-ON signal high PW-OK low level, other voltage output. ATX power supply from standby to launch managed state by using a wire to ATX plugs 14 foot PS-ON signal to end with either 3, 5, 7, 13, 15, 16, 17, of a shorted, PS-ON signal to zero level, PW-OK, + 5VSB signal is high level, switching power supply fan rotation, ATX plugs + 3.3V, + 5V, + 12V output.
I. common failure analysis and processing

1. power-output

When the power in a load case, measuring out the output DC voltage is that power no output. This should open the power check fuses, fuse fuse situation analysis of the fault.

1) fused with black

Description of serious short circuit to check the rectifier filtering and Power Inverter circuit.
(1) AC filter capacitor C3, C4 for AC surge voltage breakdown and short circuit, some ATX power supply AC filter circuit is more complex, you should check whether there is short circuit components.


(2) Exchange the master back to the road and bridge type rectifier diode breakdown in one. The cause of the damage: DC filter capacitor C5, C6 is 330 μ μ F or 470 F bulk electrolytic capacitors, instant charging current of up to 20A above. So the moment the bulk of the surge current easy to result in a performance bridge rectifier slightly worse in rectifying tube burned. Other AC surge voltage will breakdown rectifier diodes and short circuit.
(3) rectifier filtering circuit DC filter capacitor C5, C6 breakdown and even burst. The cause of the damage: due to the large volume of electrolytic capacitor voltage 200V, General while actually working voltage reaches around 150V, close to the rated value. Therefore, when the input voltage fluctuations or some poor quality Electrolytic Capacitor, prone to breakdown capacitance. In addition when the electrolytic capacitor leakage occurs, severe fever andburst.
(4) DC converter circuit power switching transistor VT2 and reversing VT1, VD1, VD2 diode breakdown damaged. Damage: after rectifier filtering output voltage typically up to 300V, inverter power switching valve's load and inductive load, leakage inductance of the peak voltage may be close to 600V, VT1 and VT2 voltage Vceo only 450V. So when the input voltage is high, some pressure low switching valve will be breakdown. So you can choose to withstand higher power switching valve.

2) fuses but not black

Description is not a short circuit caused the fuses.
(1) powering up the blowing of the insurance, the moment is a moment of great current insurance thrust, as power DC filter capacitor charging current.
(2) use the blowing of the insurance, much too large to load.

3) fuse does not fuse

As the power supply is no output. The fuse is intact, you should review the power control circuit for open circuit, short circuit and over-voltage, over-current protection circuit is the movement, the auxiliary power is intact.
(1) AC input circuit current limiting resistor THR open circuit, measuring less than 300V DC voltage. Switching power supply with 220V direct rectifier filter circuit, when connected to AC voltage is a large surge current (capacitor charging current), inrush current limiting resistor or easily cause fuses.
(2) auxiliary power supply output voltage without + 5V. Should be focused on checking the auxiliary power supply circuit related components, such as auxiliary power circuit VT15 oscillation tube, pipe, VD30 VZ16 voltage, short circuit diode breakdown VD41, current limiting resistor R72 or starting resistance R76 circuit breakers, etc.
(3) pulse width modulation chip TL494 damage, voltage comparator LM393 damage. In addition such as IC10, VT7 short-circuit, makes the IC1 's voltage is 4 feet high, which is in the standby state.
(4) DC output short circuit, short circuit protection will play a role. The phenomenon is turned on or off instant power indication, and then immediately turn off. You should carefully check the ± 5V, 12V line is ± damage or breakdown of on the circuit board. Generally the most common + 5V DC circuit of Schottky Diode breakdown.
(5) DC output over voltage, over voltage protection function. You should check the + 5V, + 12V automatic voltage control circuit damage, make automatic voltage regulator control failure.

2. controlled powered DC power no output

(1) T2 original side VT3VT4 drive pipe damage, larger R54 resistor;
(2) half bridge converter circuit interrupter VT1 and VT2 at least one open circuit;
(3) anti bias smaller capacity capacitor C8 or open circuit.

3. the power supply has a power output, but not post

This is mainly because the power of the signal delay time not enough PW-OK or no output. Power on, using a voltmeter measurement PW-OK output (power plug, 8-foot) have no + 5V. You should check the comparator LM393 damage. If the delay is not enough, you should check the delay circuit resistance and capacitance C60 R104.

4. power supply load capacity difference

Power load capacity difference mainly manifested as: power in light load cases, if only to the system board, floppy drive, power supply, works, and in with the big hard drive, expand the other devices, power work cannot properly. This is usually a power converter circuitSwitching tube VT1 and VT2 performance is not good, filter capacitor C5, C6 insufficient capacity. Replacement filter capacitor should pay attention to the capacity of the two capacitance and voltage values must be consistent.

5. power supply output voltage allowed

If only one rail voltage deviation ratings, and other various stalls voltage are OK, it is the rail voltage integrated voltage circuit or rectifier diode is damaged. If all deviations from the nominal value is determined by the IC1 's 1, 2, foot error amplifier, R39, C32 error amplifiernegative feedback loop, R33 and R34 sampling resistance, R35, constitute a + 5V, + 12V automatic voltage control circuit is faulty.

To replace the power supply circuit diode is to note that because the inverter frequency is high, generally greater than 20kHz, load current is large, so the power supply + 5V rail use SBD Schottky rectifier diode, also be used for the rest of the stall recovery characteristics of high-frequency rectifiers FRD. So when you want to replace as much as possible to find the same type of rectifier diode, avoid damaged again.

6. the fan will not turn or noise

Computer power supply fans are usually connected to the + 12V DC output DC fan. If the power input and output all normal, but the fans do not go to the fan motor is damaged. If a sound, its one of the reasons is because the long-term operation of the machine or transportation of intense vibrations caused by fans of loosen the four captive screws; the second is the fan too many internal dust or oil-impregnated bearings to the lack of oil, as long as the time or join the right amount of advanced lubricants, the fault can be excluded.