⚫ Measure the voltage regulator Z1 voltage at the switching power supply, should be
about 12V (12V under no load, 14V or so under loaded conditions), the 12V is for the
UC3844 pin 7 to provide the operating voltage (3844 in the foot of the under-voltage lockout
function of 10V), if it is not a stable 12V, then it shows that the switching power supply
UC3844 front-end failure, to find the VCC power supply circuit; UC2844 corresponding to
the corresponding 8-pin voltage of 5V, the voltage is for the 3844 pin 4 to provide oscillating
voltage, the absence of the voltage will also lead to switching power supply problems; with
an oscilloscope to measure the 6-pin and 5-pin, 6-pin there will be a current pulse, the test
does not have the current pulse, basically the 3844 problem, and if all of the above tests are
normal, then the 3844 problem. If all the above tests are normal, then the 3844 itself and the
previous circuit are basically no problem, you only need to test the corresponding vice-side
voltage circuit and the corresponding voltage feedback circuit.
⚫ In the past, there will be a switching power supply short-circuit hiccups phenomenon,
that is, to measure the transformer voltage on the secondary side of the transformer will be
a moment, a moment without the phenomenon of the need to test the corresponding D4, D15
diode whether the diode is broken, the diode is broken, is caused by the switching power
supply failure rate of the device is very high; in the case of D8 diode, to see if it is damaged,
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