Author Topic: Beware, SIUI Medical Ultrasound PCB  (Read 1357 times)

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Offline Muanpuia

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Beware, SIUI Medical Ultrasound PCB
« on: July 29, 2014, 11:10:41 pm »
     Hello, beforehand this is my first post so please excuse me and let me know if i post this in the wrong topic.
Last month i happen to stuck in a repair of Portable Monochrome Ultrasound Scanner branded SIUI(chinese) Model no CTS-5500.
     The problem is kind of intermittent blown fuse and i promptly apply series bulb trick to see if its safe to just replace the fuse and its running fine. But everytime i change the fuse, it blows again after 2.5-3minutes average. Then test run each section (crt display, D/A converter, Oscillator....) and its all seems fine.
     After a long trial and error (this system has two probe socket) the reason fuse blows intermittently is a result of intermittent abnormal load in probe output socket HV switching PCB. This board inputs US signal of +5v level that switched between -100 and +100v, and a short circuit happens intermittently between -100v to ground (more frequent whenever 4B scanning mode is used) I have so much trouble finding out which particular IC among 24 of them is bad.
     Thermal test gets me no where, radio test also not helpful, so i remove all 24 ICs. Then i dry run it, to my amazement the short circuit is still there! Ive already done too much to giveup now, so i remove all -100v related parts again. It really pisses me off, the S/C is still there!!! So to my last resort im taking the risk. I get readymade home fan speed controller (triac type, not rheostat), Transformer (220v - 6v) and ignition coil that i remove from my RE, i wire them up like in the photo.
     Starting from minimum position of fan speed controller, i raise the fan speed :) in small increment and im so happy to see these old parts are doing just what i expected. I turn off the light and raise the fan speed, i see a little spark at via of PCB hole that the probe socket sits.
     So i think when the probe socket is screwed on, it compress the pcb all the time which somehow flattens some layer sandwitched at that point, the area getting larger and shorted with the wall of via. I really jump for joy and i think you can all imagine what im supposed to do then.
     Finished, play around with it, yet its a pity that i dont know/understand the echo image of my own body, looks like fluids running wildly inside me. I think theyre happy too......haha.
     I post this hoping that someone with this kind of problem might find it helpful and save time to learn something else.
Thank you eev
 


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