Maintenance of Repeated Breakdown of Rectification Diode in HY-U19 Electromagnetic Stove for Little Swan 1

Inspection and analysis: A small swan HY-U 19 electromagnetic stove, the indicator light does not flash after power on. During inspection, it was found that the D4 (RF107) rectifier diode in the motherboard circuit was broken down, and there were serious burn marks on the mounting board positions of its two poles. Other components were checked and no abnormalities were found. After replacing the D4 (RF107) rectifier diode, the electromagnetic stove resumed operation, but after a few minutes of operation, the D4 (RF107) rectifier diode broke down again and wasdiode damaged. Therefore, it indicates that there is a hidden fault in the motherboard circuit. In this type of electromagnetic stove, D4 (RF107) is mainly used for 18V low-voltage rectification, but it also has short-circuit protection function (as shown in the attached local circuit). After replacing D4 (RF107) again and briefly powering it on, it was found that the surface temperature of D4 was high, which may be due to the current passing through D4 exceeding the set value. However, the main factor affecting the rise of D4 rectification current should be the oscillation timing circuit. Therefore, it was determined that the timing capacitor of C3 (1nF) was faulty, and after replacing it, the fault was completely eliminated. Summary: In the attached figure, C3 and R6 form a series RC constant timing circuit, which, together with U1 (13005), T1, D4, Q1, and R4, R5, forms a self-excited parallel switching power supply circuit. The working principle is briefly as follows: 1. Self excitation oscillation. In the attached figure, the primary windings of U1 and T1, R4, R5, C3, R6, etc. form a self-excited oscillation circuit. When the mains voltage (AC220V) and full bridge rectifier circuit are connected, a+300V voltage is formed through D11, R102, and the primary winding of Tl is applied to the collector of U1 (13005). At the same time, the+300V voltage is applied to the base of U1 (13005) through R4 and R5 starting resistors, causing U1 (13005) to start conducting. Current flows through the primary winding of T1, forming an induced electromotive force with positive upper and negative lower sides,diode