Rencheng Repair Case: Repair of Philips iU22 Ultrasound Power Supply Failure

Machine Type: Philips Color Doppler Ultrasound Diagnostic Instrument

Machine Model:Philips iU22

Fault Phenomenon

　　Turn on the power, the system enters standby mode. After pressing the power button (On/Standy), the system starts the power-on initialization process, but only lasts for about 3～4 seconds, then the system suddenly loses power during the startup process, and the blue AC power indicator light on the back of the machine starts flashing. At this time, pressing the power button again will not result in any response. Turn off the AC power switch, then turn it on again, and press the power button again, the fault remains. According to the operator, sometimes by operating the power-on process multiple times, it can occasionally be successfully started. Once the machine is running, it can operate normally, but the next day after shutdown, it cannot start normally again.

Analysis and Repair

　　Based on the analysis of the fault phenomenon, it is suspected that the power supply part of the system has failed. The DC power supply unit of the iU22 is installed in the power box at the bottom of the device, and the left side cover of the device needs to be opened to observe it. The AC power supply unit is installed at the lower rear of the device and has an air circuit breaker.

After observation and analysis, it was found that the iU22 power supply system mainly includes six parts:

1. AC unit (including a +12V auxiliary power supply)
2. +12V DC power supply module
3. +3.5V, ±5.3V, ±15V and +48V DC power supply module
4. +12V DC power supply voltage transformation, monitoring and distribution circuit board (hereinafter referred to as A board)
5. +3.5V, ±5.3V, ±15V and +48V DC power supply monitoring and distribution circuit board (hereinafter referred to as B board)
6. High-voltage power supply module

220V AC power is supplied to the DC power supply module through a relay, and the output of the DC power supply module is sent to the back-end and front-end circuits through the voltage monitoring and distribution board. The auxiliary power supply +12VSB is directly powered by 220V AC, and starts working once the power switch is turned on, and the blue power indicator light is lit. +12VSB is responsible for providing standby power to the A board and B board, and at the same time, the B board converts +12VSB into +5VSB to power the back-end circuit.

When the power button (On/Standy) is pressed, the power-on control circuit in the back-end circuit sends a PS_ON signal, which is transmitted to the B board, and the B board sends a Power_on signal to close the driving relay. After the relay is closed, the DC power supply module starts working, outputs various voltages required for system operation, and provides them to the front-end and back-end circuits through the A board and B board. There are voltage window comparators on both the A board and B board to monitor the DC voltages. When the output voltages of the various power supplies are within the allowed range, the A board and B board will output a DC_OK signal, which after an "AND" operation, forms a PW_GOOD signal to notify the mainboard that the power is normal, and the system can be initialized.If the output voltage of the DC power supply is too high or too low, the protection circuit on the A board and B board cannot generate a normal DC_OK signal, so the system main

board cannot receive the PW_GOOD signal, and will withdraw the driving signal of the relay. After the relay is de-energized, the AC input will be disconnected, completely cutting off the power supply of the host, thus ensuring the safety of the system.

Troubleshooting

First, test the DC power supply module. Remove the two power supply modules from the power box, connect them directly to the 220V AC power supply, and check the output voltage of each group, the results are normal. Then, check the protection circuit part located on the B board. After repeated checks and experiments, it was found that an ICABT573AD (8D latch with three-state output gate) on this board was damaged, resulting in a short circuit of the DC_OK signal transmitted from the A board, causing the protection circuit to judge that the power supply of the A board was abnormal, thereby cutting off the AC power supply. After replacing a new ABT573AD, the system recovers to normal, and the fault is eliminated.