Analysis of Common Failures in FUJINON Electronic Endoscopes

EPX-201 main unit, after about one year of use, the first bulb burned out during use, and the machine automatically switched to the backup bulb. The operator did not replace the damaged bulb, and after about a month, the second bulb burned out. After replacing it with a new bulb, it burned out as soon as it was turned on.

Fault Analysis and Repair:

Based on the failure phenomenon, we suspect that the bulb voltage is too high.

The voltage at the E1 and E2 terminals is AC23V, and the voltage at the C31 terminals is 31V, which is normal. The voltage at the T1 and T2 terminals of the faulty machine is 31V, which is much higher than the rated voltage of 15V for the bulb. Q31 (2SK1292) has exploded and broken down.

Given the high failure rate of Q31 and the characteristic of explosion, we consider that the manufacturer may have chosen components with a smaller current margin during design.

According to the parameters of 2SK1292 (20A/100V, 35W), plus the maximum voltage of about 32V after D31 rectification, replacing 25K1292 with a higher parameter field-effect transistor 25K1346 (25A/60V, 40W) yields good results. In addition, Q31 is provided with excitation voltage by Q33 (2SC1815) and Q34 (25A1015), while Q35 (25C2655) is an error and control amplifier. Checking Q33, Q34, and Q35 according to experience, we found that Q33 and Q34 were broken down, while Q35 was intact.

After replacing the damaged tubes and restoring the circuit, without the bulb, the voltage at the T1 and T2 terminals was measured to be 16V. Adjusting RV31, the voltage at the T1 and T2 terminals was set to 14.5-14.9V. After restoring the mainboard connection and connecting the bulb, the machine was turned on. The bulb brightness is controllable and normal.

Σ200 main unit, the bulb does not light up when the power is turned on.

Fault Analysis and Repair:

Measuring Q31, Q33, Q34, and Q35, it was found that Q31, Q33, and Q34 were all broken down, while Q35 was intact. After replacing Q31, Q33, and Q34 and turning on the power, when preparing to measure the voltage at the T1 and T2 terminals, a puff of white smoke came from the Q31 position. The power was immediately turned off for inspection, and it was found that Q31, Q33, and Q34 were damaged again, while Q35 remained intact. It is suspected that Q32 and the power supply circuit have faults.

Q32 and D32 were measured to be intact, while the operating voltage of Q32 is provided by R31, C35, and D33. After checking these components, it was found that the voltage regulator D33 was open. Replacing it with a 10V/0.5W voltage regulator, and confirming that other peripheral circuits are intact, all damaged components were replaced. After turning on the power, RV31 was adjusted so that the voltage at the T1 and T2 terminals was 14.8V. After restoring the mainboard connection, the machine worked normally.

During the repair, it was found that Q33 and Q34 were damaged simultaneously more often. Therefore, after replacing Q31, these tubes and the surrounding circuits should be checked together. Do not rush to turn on the power after only replacing Q31, which may cause damage to new components or expand the fault.

Points to Note During Repair

(1) When the mainboard and mirror are not connected, the automatic bulb switching function cannot be performed, the lamp holder is not in the initial position, and the bulb cannot be lit. At this time, the mainboard can be connected first, and the mirror drive connector can be plugged in. Turn on the power switch, and after the lamp holder returns to the initial position, remove the mirror to observe the condition of the bulb.

(2) The mainboard connection and the outer cover must be restored before the bulb can be tested for a long time. Otherwise, due to poor ventilation and heat dissipation, Q31 will overheat and burn out.

(3) After the repair is completed, Confirm that both bulbs are intact to prevent the automatic bulb switching function from repeatedly operating as soon as the power is turned on, or the phenomenon that the doctor is unable to switch to the backup bulb after the bulb burns out during the examination, leading to confusion.

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