Board end power hardware debugging bug

Project scenario ：

problem 1：MC34063A Negative pressure circuit commissioning ,MC34063A It is a switching power supply commonly used to generate negative pressure , But last year I spent PCB Board for debugging , The voltage generated by negative pressure is 0V.
problem 2： use MP2359 Switching power supply generates 5V voltage ;
problem 3： This step of debugging is successful , however AMS1117-3.3 The chip cannot generate 3.3V voltage .

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Problem description

problem 1：MC34063A Negative pressure cannot be generated ？

problem 2：MP2359 The chip is changed PCB After plate welding , Suddenly cannot produce 5V voltage ？

problem 3：AMS1117 The power supply module composed of cannot 3.3V voltage

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Cause analysis ：

problem 1： This problem dates back to last year 12 month , I came across , At that time, I had no experience in hardware circuit debugging , Encountered this problem and asked the seniors and teachers , But it didn't solve the problem . I don't bother debugging Replaced a negative pressure generation chip MAX765.
This year I used this chip again , I just started debugging on the board and still can't produce -5V voltage , I can't think of an answer ！ Obviously, it refers to the circuit connection according to the data manual , Why is the output voltage 0 Well ？
Finally I changed MC34063A chip , Debugging successful ！
So the scrap rate of this chip is relatively high , If the debugging is not successful, change the chip for debugging .

problem 2： The first thing that makes people confused is that A The board mode is successful MP2359 If you change a development board, you can't output , Looking at the data book, I found that it was me PCN The upper diode package is painted upside down , The diode is connected reversely . The diode is connected reversely , The supply voltage flows directly through MOS switch , No subsequent capacitance and inductance , Naturally, it doesn't export 5V.

So I rewelded the diode , But the chip still can't output 5V voltage , I have encountered this problem once before. It is also after the diode is turned on , Re weld the diode , The chip doesn't work either . So I guess that the diodes connected in reverse , Right on , The circuit goes on directly .
The internal structure of the chip is as follows ：

under these circumstances , It is equivalent to the moment when the switch is closed , Short circuit of power supply , The instantaneous current is very large , Make the chip burn out ！
To verify that the chip has burned out , I welded a new one MP2359, There is no wrong diode connection in this circuit , At this time, the circuit successfully outputs 5V.

problem 3： It's solved 5V Problems caused by power supply voltage , that 3.3V Why can't the power supply voltage be generated smoothly ？
At this time, the senior suggested that my peripheral circuit might be short circuited , The voltage stabilizing module cannot output correctly .
So use a multimeter to test 3.3V Whether the peripheral output circuit is short circuited , The final measurement result is that the peripheral circuit is short circuited .
First, I will test the components without welding PCB Whether the board exists 3.3V Short circuit condition , The test found no such situation , Therefore, the components are short circuited or broken .
All components of my development board have been welded ,3.3V Supply power to multiple modules , It is troublesome to look for peripheral short circuit devices ！
So I'm in the new PCB Re weld components on the board , Finally, it is confirmed that it is the problem of single-chip microcomputer welding , After re welding the components , The power module test is OK ！

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