Olympus 260 endoscope repeatedly restarts on power-up

 Based on the analysis of the system structure, the cold light source, electronic gastrointestinal endoscope, keyboard, and workstation are irrelevant to the system power-on. After removing each of the above one by one and powering on, the malfunction phenomenon remains unchanged, which rules out the possibility of their failure. The display is normal, which also rules out the problem of the monitor. The fault is mainly located on the CV-260 image processing unit.

     First, M4T28-BR12SH1 was measured separately, with a 2.3 V output, indicating that the IC chip is normal. Upon closer observation, it was found that when restarting, 4 LED indicators on the video buffer controller board flashed, while only one was lit normally. Measuring the power supply voltage output, there was no change whether restarting or with or without load, ruling out the possibility of a power supply board failure. Due to the lack of a same model motherboard for replacement, the repair was stalled. 

   Through the analysis of the interrelationship between various functional modules inside the CV-260, the power supply board provides power support to other boards. The measurement results have ruled out the possibility of its failure; the interface board connects to the electronic endoscope and receives the image signals transmitted from the electronic endoscope. Since the electronic endoscope is not connected, this function is idle. Attempting to remove the power supply of the interface board, the power-on failure remains, indicating that the fault did not occur on this board; the button board is a combination of micro switches and LED indicators. Removing it and testing the power-on failure remains, thus ruling out the possibility of a button board failure.

       According to the user's description, after restarting half a year ago, all functions were normal, indicating that the microprocessor, CPLD, and memory and other important IC chips are functioning normally. Even if various video decoding output circuits fail, it should be a video output abnormality, and it should not cause repeated restarts. Therefore, the possibility of a failure in the lower board of the main control board is small.

       The fault range is narrowed down to the upper board of the main control board. Repeated restarts are either due to program errors, repeatedly reset by the watchdog program; or abnormal power supply circuit. If it is a program error, the frequency of repeated restarts will not gradually increase, thus judging that the probability of a program error is small. Abnormal power supply circuits are generally seen in older equipment that has been used for a long time, which is consistent with the current fault situation. Abnormal power supply is generally due to power supply problems or a failure of a certain load.

     Checking the technical parameter documents of each functional IC chip, it was inadvertently discovered that they are all powered by 3.3 V, while the only input voltage of this board is 5.2 V, so there must be a voltage conversion circuit that converts 5.2 V to 3.3 V.

     Through the analysis of the main control board upper board, its power supply circuit is shown in the figure below, where UNR3.3/8 D5T (U631) is a DC-DC conversion module that converts the input 5.2 V to 3.3 V to power various IC chips, and the output of LMS1587CS-ADJ (U629) is 1.8 V.