The printer switch power supply is generally simple, and its maintenance method is consistent with the conventional switch power supply.

Maintenance example
Example 1 failure: lq-1520 needle printer, power on the printer indicator light is not on, word car does not move.
Analysis and maintenance: according to the fault phenomenon, is generally caused by power failure. First check the ac fuse of the switching power supply, found that the fuse has been blown, the whole bridge QL1 has a bridge arm is broken. It indicates that the ac input part of the switching power supply has short-circuit device. Two switch tubes VT101 and VT102 (2SC4058) were punctured by the multimeter, and the resistance R111 overcurrent was burnt out. After the above mentioned components are replaced, there is still no voltage output in the power supply, and 310V on the collector of VT102 is normal, indicating that the primary side of the power supply has not started. Check VT103 and VT104 and find that the base resistance R104 and R106 of VT103 and VT104 have been burnt out. After replacement, the power supply works normally.
Example 2 failure: C41SX printer, the green light is not on, the printer does not work.
Analysis and maintenance: check the (1) pin of CN2 without +36V voltage, check the FU1 fuse intact with +300V voltage, and check the C51 with +36V voltage. Power off, check insurance resistance RS1, found damaged, and then check the main circuit board found C37 short circuit. After replacing the safety resistor and electrolytic capacitor, the operation returns to normal.
Example 3 failure phenomenon: HP1010 laser printer, the switch power supply gives out a "squeak" sound.
Analysis and maintenance: the switch power supply makes a "squeaking" sound, which generally has three conditions: one is the loss of capacity of +300V filter capacitor C107; The second is the load fault, the power supply in the protection working state; Third, the power supply operating frequency is too low.
The "squeaking" sound of the switching power supply can be heard, which indicates that the starting circuit, positive feedback circuit and protection circuit themselves are basically normal. The reason may be that the power supply is unstable, the load is too heavy or the pulse width control transistor is strong, and the power supply is in the protection working state or low-frequency working state. During maintenance, firstly visually observe the +300V filter capacitor C107, and find that the capacitor is bulging in the middle, remove it, measure with the multimeter, and there is no capacity. After replacing C107, the fault is removed.