Special Condition (0411 /06.18) - Tatung OMNISCAN SERIES Service Manual

6.6 SPECIAL CONDITION
1. 0411 (2SC4288A) DEFECT WHEN POWER ON.
2. 0411 (2SC4288A) DEFECT DURING
30
MINUTES WARM UP.
3. 0618 (2SC3894) DEFECT WHEN POWER ON.
4. 0618 (2SC3894) DEFECT DURtNG
30
MINUTES WARM UP.
POSSIBLE SITUATION
SURGE VOLTAGE
The transistor defect when power on. The problem usually come from the SURGE VOLTAGE on the
collector, the SURGE VOLTAGE which is much higher than the transistor rating. It break through the
transistor junction among collector, base and emitter.
DRIVE CURRENT
The transistor defect during warm up. The problem usually come from the lack of enough DRIVE
CURRENT on the base, the lack of enough DRIVE CURRENT, caused the increasing of the impedance
(collector to emitter) of the transistor ..
Finally the THERMO-RUN-AWAYhappened inside the transistor.
Both of the situation will damage the transistor causing the short circuit between collector, base or emitter.
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