Hi Charles, We'v found the reason why the chips are damaged and we'v solved the problem. The switch we use is a mechanical switch, and when we power on, the +50V power goes up very quickly. Since there is a capacitor about 100uF between -50V and GND on the TX board. There is a large current on the GND when power up. Since the 3.3V GND and -50V GND are connected and the 3.3V GND is near the board and the +50V GND are on the far-end. The pulse current makes a big Voltage jump on the 3.3V GND, about 4.5V. So that makes the 3.3V up to 7.8V which damaged the chip. We tried to make the 3.3V GND and -50V GND conneted in a Star Topology, which makes the jump only a little smaller, still has a voltage about 7V. So, we take away the mechanical switch and use the power on-off button directly. Using the Power on-off button, the output of the power goes up much slower that using the mechanical switch. So the pulse current is very small, so the Voltage is very small. That solves our problem. Now, we have used the TX board to drive our ultrasound probe successuly. ^ ^ Thank you very much for all your help! Yours sincerely, Frank
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