- berrytips
- June 2, 2023
- 0 Comments
While my son, who was studying Computer Engineering in University, was trying to make an operating system for his Raspberry Pi, he accidentally caused a short circuit in the Raspberry’s GPIO pins. Since the program he was trying to make had not yet reached the stage of displaying the screen, he activated a pin on the GPIO and used it for debugging purposes. After not getting an exit voltage from output for a long time, he suspected that the device was malfunctioning. I wanted to help him then I inserted a working SD card and connected the device to the display. There was no image. The pin that should be 3.3V (No1: can be) was read 0V. When considering what was causing the malfunction, we thought that the Multimeter’s probe might have short-circuited pins 3.3V to 5V.
After doing some research on the internet, I found out that the MxL7704-AQB IC that generates the voltages on the circuit may be faulty. This is a regulator IC that has 4 buck converters inside . This device provides 4 different voltage levels for PCB. These voltages should be as seen in the figure. However I read values like 0.15 – 0.2V.
Replacing IC
To repair this Raspberry Pi ,I ordered this chip through AliExpress at a cheap price. A hot air blowing station is needed to change this. The underside of the chip is also soldered to the PCB for cooling purposes. That is why it is so difficult to disassemble it with a soldering iron. As a matter of fact, it is necessary to have good soldering skills when disassembling and installing it. Before the hot air heated the chip enough to dismantle it, the solders of the tiny SMD parts in the surrounding area melted and were replaced of flied away by the wind. Some of them lost. To figure out what was where, I had to study the RPI chart and measure the tiny pieces one by one. They are so small that it was difficult to even touch the two ends of the probe at the same time.
Conclusion
I had to buy some components again. I finally put everything in place, but the voltages remained low. Although they were better than before, they were not what they should be.
Unfortunately, I still could not repair the card and took a break. While doing internet research on this failure, I also found out that there are Raspberries that bricked due to similar failures. I think it is possible to fix this. Maybe there are other problems with the circuit. For this, I will continue to look for faults, isolating each regulator outlet. Maybe I overheated the chip and burned it.
I saw a topic on RPi official forum that this IC registers must be correctly programmed over I2C interface to run compatible with RPI3B+ and RPI4B boards. I will try this later. Because I was dismounted the IC. Here is the related links
https://forums.raspberrypi.com/viewtopic.php?t=314996 (A personal Blog)
https://repair.wiki/w/MXL7704_(Raspberry_Pi) (Register values)
Raspberry Pi3B+ Reduced Schematics
