The PSU is designed to convert the 220V mains voltage into the voltages necessary for the stable operation of the consumers connected to it. PSU also provides stabilization of output voltages, provides protection against short circuits, and provides the necessary power, depending on the connected load.
This material was prepared by Bgacenter teachers, as part of the course – repair of switching power supplies.
To ensure the load of the miners, UPSs of various capacities are used. This material discusses in detail the PSU used for different ASIC models.
The APW7 design includes:
The main function is performed by the board with the elements located on it.
Elements located on the printed circuit board of the UPS:
So, the APW7 switching power supply works according to the following principle:
Switching power supplies are characterized by the following malfunctions:
Repair of the APW7 power supply begins with an external inspection. Attention should be paid to the presence of mechanical damage and previously performed repairs. By the absence of a sealant and an unwashed flux, it can be assumed that a repair was carried out earlier – the board was soldered.
We start diagnosing the board by finding the power filter capacitors. They are usually large in size. We look at its ratings, as we see from the inscription on the capacitor, it has parameters of 450V 470 microfarads each.
For further repair, it is necessary to discharge it, regardless of the time it has been out of service. With a tester in the DC voltage measurement mode, we make sure that there is no voltage at the terminals of the capacitors. To do this, we connect the device from the side of the printed circuit board. If there is voltage, we discharge the capacitor with a 60W incandescent lamp and check again with a tester for the absence of voltage.
Only after this procedure can further repairs be carried out. To facilitate troubleshooting, we make sure indirectly that there is no short circuit in the main power supply circuit of the synchronous rectifier along the + 12V main circuit.
To do this, we apply the black probe to the output located at the bottom, and the red probe to the output located at the top, we should see serviceable field-effect transistors (the readings of the MS-319 multimeter (pointer) should be about 20 ohms).
Меняем местами щупы, происходит заряд конденсаторов и сопротивление увеличилось, это говорит о We swap the probes, the capacitors are charged and the resistance has increased, this indicates the health of the rectifier.
We continue the repair, proceed to the diagnosis of the power unit. With a tester from the mains power connector in the continuity mode, we check the input of one wire to the diode bridge (variable designation input). The tester should show 0 (or emit a kind of beep), which immediately indicates the health of one inductance filter circuit and the integrity of the printed conductor and fuse.
Similarly, we check the second wire, but to a different output of the diode bridge. This indicates the health of the second conductor.
Repair is necessary if the multimeter shows non-zero readings. In this case, we are looking for a break, we eliminate it. In this case, everything is fine.
Next, we check the resistance between the two network control entry points. It should be high (tester in MOhm mode). The measurement showed high resistance in this case. This indicates the absence of a short circuit at the input and the serviceability of the varistor. After making sure that the input unit is working, we check the diode bridge.
The method for checking the diode bridge is standard, the diode continuity mode. After making sure that it is working, we examine the PFC block and its circuits. We check MOSFET (field effect transistor). We put the probes between the gate and the source, then the gate and the drain – the resistance should be high and the tester does not show us anything. It is right.
Next, check the drain-source. When a red probe is applied to the source and black to the drain, we will see a voltage drop across the diode of the order of 0.470 mV. In the reverse application of the probes, we will not see any drops. We conclude that the transistor is in good condition.
To measure the control pulses at the gate of this transistor, it is necessary to use an oscilloscope. If there are pulses, we conclude that the microcircuit is in good condition and the pulse is applied to the gate of the field-effect transistor.
Next, we check the circuit of the auxiliary power supply + 12V, assembled on the ICE2QR4765 microcircuit indicated according to the circuit diagram. To do this, in the diode continuity mode, we put one probe on the + high-voltage capacitor, and the second on pin 4 of this PWM chip, we make sure that the auxiliary source transformer winding is intact.
Repairs must be carried out with a discharged high-voltage capacitor and the UPS disconnected from the mains!
After that, we check the operation of the main PWM and its power supply circuits according to the electrical circuit diagram. Next, we check the semi-bridge circuit on MOSFET transistors. They are checked with a multimeter in diode continuity mode. Initially, for each transistor, we check the Gate-Source junction, the multimeter should show OL, this indicates that the junction is working (it is not broken).
The next step, in the resistance measurement mode, check the Gate-Source. At the same time, we check the resistance of the matching driver. The resistance of a good output should be between 10 and 20 ohms.
As can be seen from the measurements, this indirectly indicates the health of the transistors. In case of doubt about the serviceability of the transistors, they must be soldered and checked separately. The LCR-T4 digital meter is used to test transistors.
Then we check the Drain-Source junction for a short circuit. To do this, set the red probe of the multimeter to the Source, and connect the black one to the Drain. The voltage drop in the diode continuity mode should be 0.434 V. This indicates the health of the field effect transistor.
When applying the probes in the opposite direction, the multimeter shows OL.
After successfully identifying faults and repairing damaged elements, the unit must be tested. To do this, the UPS is connected via an isolation transformer to the mains supply.
Then, an electronic load of the required power is connected to the PSU to check for operability. Testing is performed within 1-2 hours. To avoid repeated repairs, it is not recommended to turn on the UPS without a connected load.
During the repair of the UPS, it becomes necessary to check the elements. To do this, you need to solder the corresponding element from the printed circuit board. Soldering is important to be done carefully, using a soldering iron of the required power:
If the UPS worked in violation of temperature conditions (overheated), then when the compound is removed, the SMD components can be torn off the printed circuit board. It is important to remember this, and with further repairs, restore the strapping to the board.
When repairing the UPS, Rose alloy is used to reduce the temperature of the factory solder and prevent damage to the lead wires.
During installation it is necessary to solder on:
After repair, before taking measurements on transistors, it is important to lower the temperature of the UPS, since in a heated state, the keys are open.
Before soldering newly installed components (transistors), their leads must be cleaned and tinned.
After soldering, it is necessary to wash with alcohol or other cleaner those places where soldering was performed.
Equipment used during UPS repair, consumables: