The Little Swan washing machine is not working, and all function button switches have failed.
Fault Phenomenon: According to the user's introduction, after the fully automatic washing machine is connected to the power supply, none of the indicator lights are on, all function button switches have failed, and it cannot operate.
Fault Analysis: Based on the situation described by the user, such faults usually occur in the whole machine's power supply circuit or microprocessor control circuit. During maintenance, these two parts of the circuit can be checked first.
Fault Inspection:
1. Determine the approximate location of the fault
(1) After connecting the power, the 220V AC voltage applied to the primary side of the power transformer is basically normal, and the secondary output of around 14V AC low voltage has no issues.
(2) The DC voltage rectified by the bridge rectifier VDB1 and filtered by capacitor C2 is normal. The +5V voltage output from the simple voltage stabilizing circuit composed of VT10, R16, and VDZ1 is also normal, and this voltage is applied to pin 28, the operating voltage input terminal of the microprocessor integrated circuit IC1 (MN15828).
(3) Using an oscilloscope to check the oscillation waveform on pins ⑧ and ⑨ of the microprocessor control chip IC1 (MN15828) for the clock oscillator circuit is normal. However, upon checking the reset voltage on capacitor C6 at pin ⑦ of IC1 (MN15828), it was found that the reset voltage remains at a low level, whereas under normal circumstances, the voltage should rise to approximately 3.8V after resetting.
(4) Upon checking capacitor C6 in the reset circuit, it was discovered that there were cracks around the solder joint of pin ⑦ of IC1 (MN15828), resulting in a cold solder joint.
2. Fault Handling: After re-soldering pin ⑦ of IC1 (MN15828) with additional tin to make it secure, the power was turned on for testing. The washing machine returned to normal operation, and the fault was eliminated.
For more information, please contact Beijing Little Swan Washing Machine Repair Center.
Beijing Little Swan Washing Machine Repair Phone: [http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3446359](http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3446359) Technical Report.