Analysis and Maintenance of Common Faults of SANTAK UPS Power Supply

Analysis and Maintenance of Common Faults of SANTAK UPS-500 Power Supply

General method of checking for faults

1. Observation method: When there is a failure of the backup UPS uninterruptible power supply, it is necessary to first observe the flickering of each working status indicator on the control panel to determine whether the mains power supply automatic voltage regulation control circuit part or the inverter part is out. malfunction. If the green indicator light is on, the buzzer is not called and there is a 220 volt output voltage, the power supply voltage regulation part of the mains is normal; otherwise, there is a fault point; if the red indicator light is flashing or long, the buzzer is intermittently sounding or Long beep indicates that the inverter is not normal.

2, voltage test method - measure the voltage of the key point. If the AC automatic voltage regulation part fails, use a multimeter to measure the voltage of the main circuit of the mains power supply, and it will quickly find the fault: the general fault is to blow the fuse in the AC input circuit, or to transfer the control relay and automatic voltage regulation. If the fault originates from the inverter, check whether the 30A battery fuse is intact, whether the battery voltage is above the minimum limit, and whether the last-stage driving transistor is damaged or vulnerable components. After preliminary observations have not ruled out the fault, the ICs IC4 and IC8 should be checked to measure the control levels. If the working indicator light or buzzer indicator is abnormal, first check the level of each control point of IC4 (VE556 timer). The normal value is shown in Table 1. If the level of a certain control terminal of IC4 deviates significantly from the value in the table, it means that The fault occurred on the line connected to this control. If the NE556 chip and alarm indication control circuit are normal, check the level of each control terminal of IC8 (SG3524). The normal level is shown in Table 2. If IC8 pin voltage is found to be too large from the normal value in the table, the fault may originate from this connected control part or IC8 itself.

Analysis and elimination of common faults

1. Fault phenomenon: When the mains power supply is normal, Shantui UPS power is turned on, the inverter work indicator is blinking, the buzzer finds intermittent call, that is, the Shante UPS power supply is working in the inverter state and cannot be transferred to the inverter. City power supply work status.

Fault analysis and maintenance: Can not be converted to the mains power supply, indicating that the mains power supply - inverter power supply conversion control circuit failure, to focus on testing this part of the circuit. Whether the UPS-500 uninterruptible power supply is in the mains supply or in the inverter power supply state is determined by the state of the RS flip-flop comprised of IC5's two NAND gate components. Therefore, when a fault occurs in the UPS power supply that cannot be switched to the mains power supply, the state of the RS flip-flop should be measured first. When the mains power supply, RS flip-flop is "1" state, VH = "1", VG = "0", reset terminal R (VF) is high, set terminal S (VN) is a positive width pulse signal VN; Contrary to inverter power supply. Now measure the state of the RS flip-flop, measure VH is low, VG is high, is not correct, measured set S (VN) is a series of positive width pulses, is correct; remeasurement reset The terminal R(VF) is low and is erroneous, causing the RS flip-flop outputs VH and VG to be in an error state. According to the circuit connected to the set terminal S, look ahead. Test IC3 pin 8 is high and correct. IC10 pin 10 is 0.6 volt, which is wrong (it should be 3.6 volts). The forward voltage monitoring voltage V1 is 0 volt, that is, there is no mains monitoring voltage. Check the rectifier diodes D9 and D10. It is normal to measure the transformer side winding of T2 and it is an open circuit condition to find the fault point. That is, because the edge winding of the transformer T2 is open, causing the state of the RS flip-flop to go wrong, the transformer T2 is replaced and the UPS is operating normally. If the signal on the S side (VN) is incorrect, the same inspection method as on the R side can be used to test the circuit connected to it and the fault point can be quickly found.

2. Symptom: SANTAK UPS-500 uninterruptible power supply can work normally when it is powered by the mains. When the utility power is interrupted, it cannot be powered by the inverter. Fault Analysis and Maintenance: From the fact that the phenomenon can be estimated that the inverter part is faulty, the signal of each pin of the PWM component IC8 (SG3524) should be measured. It is normal to check the voltage of the battery pack first, which is 24 volts. It is normal to eliminate the possibility that the inverter cannot start normal operation because the battery voltage is too low. Disconnect the mains and measure the critical pin voltage of IC8 (SG3524): reference power pin is 5V, normal; block 10 pin is 0V, normal; compensation pin 9 pin is 2.4V, normal; drive output End 11 and 14 feet are 0 volts, no output, abnormal; drive input 12 feet and 13 feet are 0 volts, also not normal. It can be seen that the voltage at the input of the drive is not normal, causing the output voltage to be abnormal. The bases of transistors Q7 and Q8 are measured to be low level (causing Q7 and Q8 to turn on and drive input to be low). Incorrect, their bases are connected to pin 4 of IC5 and IC5 is tested 5 The foot, which is low, is normal. After passing through the NAND gate IC5, pin 4 is still low, indicating that the IC5 is bad. Replace the IC5 and the CPU can work normally. The fault is eliminated.

3, the phenomenon of failure: UPS-500 work in the city, the power transformer has a lot of noise. Fault analysis and maintenance: When the load of the transformer is too heavy, or the work is unbalanced and unstable, abnormal noise may be emitted. When the components connected to the transformer are damaged or some of the wiring is in poor contact, the load can be too heavy. Check the secondary winding part of the transformer, did not find the phenomenon of touch line, short circuit between the windings; after careful measurement, also found no damage to components in the circuit; use the cotton swab dipped in alcohol to clean the positive and negative sides of the circuit board, Then, after the plugs and sockets are removed and re-plugged, the noise of the transformer disappears and the UPS works normally.

4. Failure phenomenon: The final drive transistors Q1 and Q2 of the inverter are damaged, so that the UPS can only work in the mains power supply state. After replacing Q1 and Q2, after the microcomputer system runs for a while, the switching transistors Q1 and Q2 are burned out again. Fault Analysis and Maintenance: From the point of view of faults, the causes of Q1 and Q2 damage are the excessive currents in the two power transistors. The factors that cause excessive current flow are: (1) Overcurrent protection failure. When overcurrent occurs at the output of the inverter, the overcurrent protection circuit does not work. A very wide modulation pulse is output from the SG3524 module to make Q1 and Q2. The medium current is too large to burn off Q1 and Q2; (2) The pulse width modulation (PWM) component IC8 (SG3524) is damaged, and the modulation pulses sent from the 11th pin and 14th pin of its final stage drive output are unbalanced, making push-pull. In the driving circuit of the type, the two arms work asymmetrically, and even the two arms are turned on at the same time, causing the power transistors Q1 and Q2 to be burned out. When the mains power is interrupted, turn on the UPS and observe the waveforms of the 11-pin and 14-pin of the last stage driver output of the IC8 component with an oscilloscope. The imbalance of the modulation pulses sent from the two output terminals is found. The Q2 turn-on time is much longer than Q1. Touch Q1 and Q2 by hand at this time, find Q2 temperature is obviously higher than Q1. From this it can be inferred that the temperature of the transistor Q2 becomes higher and higher with the prolonged supply time, and eventually it is burned out. After the Q2 is burned out, the Q1 is quickly burned out. After replacing IC8, the fault disappeared.

5. Failure phenomenon: When the mains power is normal, the Shantui UPS power supply is turned on, the AC fuse is blown, and the UPS is turned to the working state of the inverter power supply. Fault analysis and maintenance: The AC fuse is blown, indicating that the main circuit power supply main circuit current is too large. Check whether there is a short circuit in the output circuit. After testing, no short circuit point was found. In the instant of turning on the UPS UPS, we measured the output pin 14 of the IC8 (SG3524) and found that there was a modulated pulse output. This was an abnormal phenomenon. Therefore, we inferred that the inverter may also work when the mains power supply is normal. (When the mains supply, the inverter is in standby state, it is not working), both use a power transformer at the same time (mains power and inverter power supply all use the same power transformer, but can not be used simultaneously), so that Excessive current in the loop causes the fuse to blow. Starting from the IC8 working conditions, test the mains power supply-inverter power supply conversion control circuit. IC5 is found to be damaged, making VH low and VG high (normal VH should be high and VG low) when the utility is normal, causing the inverter to also work. Replace the IC5 chip and the UPS returns to normal.

6. Malfunction phenomenon: When the utility power is interrupted, the inverter work indicator is always on, and the buzzer sounds long, but the output voltage is normal, which can make the microcomputer system work normally. Fault analysis and maintenance: it is easy to judge the fault in the alarm, indicating the control circuit, should check this part of the circuit. With the oscilloscope test chip IC4 (NE556) 10 feet (reset), the voltage value of 12 volts, test 9 feet (output), the voltage value of 1.5 volts, this voltage is to control the buzzer and inverter Device work indicator (light two

Tube). Obviously, a voltage of 1.5 volts does not allow the buzzer to intermittently buzz, nor can the light emitting diodes emit light. There is a problem with the IC4. Replace the IC4 chip and the UPS returns to normal. Because the control system of the UPS power supply is a negative feedback closed-loop control system, if there is a problem, the fault may occur in any part of the closed-loop control loop, so it is necessary to test some signals and find out the real fault point.