Summary of Troubleshooting for Bosch Washing Machine Motor Speed Below Rated Value Fault
Causes of the fault include:
(1) Low power supply voltage, the solution is to adjust the power supply voltage to the rated value.
(2) Damaged bearings, need to replace the bearings.
(3) Incorrect main winding connection, correct the terminal connections of the winding.
(4) Main winding grounded or short-circuited. If the main winding is grounded, first inspect the condition of the winding damage. If the grounding point appears at the slot opening or the exit of the bottom coil and only one wire's insulation is damaged, heat the winding until the insulation layer softens, then use a scraper to separate the grounding point. Insert appropriate natural hard mica sheets or 0.5~1mm cloth-patterned laminate at the prying location, and roll with insulating paint. After repair, retest using the above method. If the grounding point occurs at the end, it can be wrapped with insulating tape and then coated with insulating paint. If the wire insulation inside the slot is damaged and grounded, the winding must be replaced. If the main winding is short-circuited, generally the short-circuited coil should be rewound.
(5) Broken rotor bars. Insert the rotor into the stator and keep it stationary, apply the rated voltage to the stator winding (for a short time). Measure the voltage of the stator winding. If the voltage of each winding is measured to be the same, there is no fault in the rotor; if the voltage of a certain winding increases, it indicates that the inner layer of the lead bar at that place has de-soldered or broken. After identifying the fault, simply solder the de-soldered places to restore usage. When soldering, the rotor needs to be heated to a certain temperature, otherwise it will be difficult to solder firmly. Remove the rotor and pass about 30V safety voltage through the rings at both ends of the rotor. At this point, there will be current passing through the rotor lead bars, generating magnetism around the lead bars. If iron powder is scattered on the surface of the rotor, the iron powder can be uniformly attracted on each conductor bar. Using the characteristic of current passing through the conductor bars attracting iron powder, the poor condition of the rotor can be checked. If it is found that a certain conductor bar attracts very little or no iron powder at all, it proves that there are pinholes or fractures on that conductor bar. The fractured end ring can be repaired by gas welding. Repairing conductor bars with pinholes or fractures is quite difficult, generally in such cases, a new rotor or motor should be replaced.
Beijing Bosch Washing Machine After-sales Service Center, September 29, 2011.