The trackball cursor on the Siemens Sequoia 512 ultrasound machine is not responding well.

The Composition and Working Principle of a Trackball

　　A trackball consists of a rolling ball, two friction wheels, two rotating shafts, two optical wheels (grating wheels), four sets of corresponding infrared light-emitting diodes and photoelectric receiving tubes, and a processing chip. Its working principle is similar to that of a mechanical mouse; it relies on the rolling friction of the rolling ball to drive the rotation of the horizontal and vertical rotating shafts. The rotating shafts drive the gratings fixed on them to rotate. Through the rotation of the grating, the photoelectric diodes are blocked and opened when receiving the light emitted by the light-emitting diodes, generating counting pulses. After processing by the chip, these pulses are displayed on the screen.

　　Fault Phenomenon

　　The trackball cursor of the SEQUIOA-512 color ultrasound machine is not sensitive, only moving up and down, while movement in the left and right directions is difficult.

　　Fault Analysis and Handling

　　Observing the trackball part of the ultrasound machine, many stains were found on the surface of the ball, and there were also many residual coupling agents in the surrounding gaps. It was initially judged that the dried coupling agent adhered to dirt, causing the above problems.

　　Open the button board casing, remove the trackball assembly, and disassemble it.

Two sponge-made friction wheels were seen wrapped around the two rotating shafts inside the trackball box. After years of friction, many sponge debris and coupling agent dust were scattered in the box, and the two optical wheels were covered with impurities, causing the transmission of the light pulse signal to be obstructed or weakened, affecting the use of the trackball. The solution is to first gently blow out the impurities in the box with a blower, then carefully wipe off the accumulated dust from the surface of the light-emitting diodes and photosensitive receiving tubes with a cotton swab dipped in pure alcohol. For the rolling ball, first wash it with clean water, then wipe it with a cleaner, and finally dry it with a cotton cloth. Note that it is best not to use detergents or other chemicals to clean the rolling ball to avoid corrosion of the ball surface.

　　After processing, the components were restored, the cover was not closed, and the rolling ball was moved in all directions by hand to make the grating rotate. The optical wheel was found to rotate unsmoothly in the left and right directions. Therefore, it was cleaned with a dry electronic cleaning agent, and after drying, a small amount of lubricating grease was added to make it rotate smoothly. It is worth noting that lubricating oil should not be used to avoid attracting dust. Finally, the components were reinstalled into the machine, and the ultrasound machine worked normally, and the fault was eliminated.

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