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 begins the power-on initialization process, but only lasts for about 3～4 seconds, the system suddenly powers off 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 cause any response from the system. Turn off the AC power switch, then turn it back on, and press the power button again, the fault persists. According to the operator, sometimes by repeating the power-on process multiple times, it can occasionally start successfully. Once the machine is running, it can operate normally, but the next day, it will fail to start normally after shutting down.

Analysis and Repair

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

Through 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 as soon as the power switch is turned on, and the blue power indicator light is lit. +12VSB is responsible for providing standby power to A board and B board, and at the same time, B board converts +12VSB into +5VSB to supply power to 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 to work, outputting various voltages required for system operation, and providing them to the front-end and back-end circuits through A board and B board. There are voltage window comparators on both A board and B board to monitor each DC voltage. When the output voltage of each power supply is within the allowed range, A board and B board will output a DC_OK signal, which is formed into a PW_GOOD signal after AND operation to inform the motherboard that the power supply 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 A board and B board cannot generate a normal DC_OK signal, so the system motherboard cannot receive the PW_GOOD signal, and the drive signal of the relay will be removed. 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.

After clarifying the basic principles of the power supply part, combined with the fault phenomenon, the reason why the power is suddenly cut off shortly after starting up must be caused by the action of the protection circuit. It can be inferred that the fault may be due to damage to the DC power supply module, or damage to the protection circuit itself.

Troubleshooting

First, test the DC power supply module. Remove the two power supply modules from the power box, directly connect them to the 220V AC power supply, and check the output voltage of each group, the result is normal. Then, check the protection circuit part located on the B board. After repeated checks and tests, 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, and thus cutting off the AC power supply. After replacing a new ABT573AD, the system recovers to normal, and the fault is eliminated.

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