Open the back cover and observe the machine was not burned components, test tube, secondary power management, switching power supply of the secondary rectifying components are not damaged. "Da Da" sound is the sound of degaussing relay. Power supply. B+ power output test. When standby 29V, press the starting button, B+ become 50V. After a few seconds. Two power output voltage when 138V, you can hear the excitation of the establishment of the sound. The two power supply voltage drops quickly to 67V, 2 seconds after the two power supply voltage again raised to 138V again, again fell to 67V. line again to stop working. This keeps the loop..
According to common sense analysis, this phenomenon should be the protection of the circuit action, the general situation is a line scan after the high pressure caused by high or other circuit exceptions lead to protection. The machine, the field scanning IC s1V9118. with IIC bus interface, the main pin function: (12) world flyback pulse input; (14) foot B + power supply error amplifier input; (15) foot B + supply voltage feedback input; (16) foot B + power switch tube current detection; (25) feet x - ray protection input (the operating voltage is 7.65 to 8.2v); (28) foot B + power excitation signal output; (29) foot 12V power supply. Firstly, the 12V power supply is normal. Observe the circuit go line. +B control and X ray protection are realized by sampling voltage of the high voltage (5) pin (AFC) pin (PCB).. The power of the starting line is about 6.v, which is not X ray protection action.. Check the high-voltage package (5) pin and all the components and the peripheral components of the STV9118, are not damaged. Instant boot for current measurement is about only 200mA, electric current is not large, desperation had to substitution sTV9118, high pressure package, rewrite the E-PROM data, even replace MCU, the fault is still, temporary maintenance in trouble.
Come down and come. Serious analysis: now has ruled out the possibility of high-pressure protection, over current protection, and where there will be protection, it is the bus? On the bus, there are three blocks of MCU, except for IC... Field scan IC STV9118, memory 24C08. there is a preview release Ic STV9269 (No. IC102). In front of the three blocks have had only IC102 did not check the substitution.
Boot test IC102 the pin voltage and found that IC102 5V power supply (10), (18) pin is always ov, Shuntengmogua, found the 5V power supply is switch transformer secondary 7V output by Q623 emission pole after two buck diode provided, Q623 also for the filament to provide 6.3V supply voltage, check the Q623, "stomach" has drum the, the above models have not see the, only vaguely see the "STC4*1 words", because the model is not complete, also check not to parameters. The analysis circuit should be NPN type tube, there is no abnormal in the detection circuit. D667 (120V / 1A) substitution load, measured filament voltage is about 5.4V, is not working properly, to estimate the beta value of large pipe. After the replacement with D400, the filament voltage recovery of 6.3V, the image of all normal.
Summary: the Q623 machine in addition to filament power supply, and also to the preview release of IC102 power supply. Due to the value of small. Cause the heat burn, causing the IC102 to lose power. MPU when the bus is on the boot to receive the IC102 response signal, then protect.
The introduction of bus technology makes communication and control between IC and CPU become easy, but it also brings us some trouble for maintenance.. Hope to draw attention to the maintenance of detours when.