Shorted 3.3v + 5v together. Is it possible to repair?

Question

I was reading through some instructions on how to add a power off/on button to the Pi and accidentally misread instructions and shorted the two end pins on a 3+B model, which appear to be 3.3v and 5v. It doesn't appear to boot now and I just see a red light when plugged in. It was powered with a 1.8A USB power supply from an old phone. Is the whole board fried? Can I replace one component and salvage it? Should I keep it for parts or just recycle it all?

Answer 1

A little instruction for people who want to resolder MXL7704-R3.

1. Order MXL7704-R3 on AliExpress (2.5$ - 3.5$).
2. You must have a hot air rework station which can heat up to 350 degrees Celsius to remove the chip.
3. You must have a soldering iron, flux, and tin. Also, a voltmeter.

How do you know that you really have a breakdown of this chip? Connect 5 volts of power (the red diode lights up) and measure the volts at the output of the chip according to the picture. Connect the black millimeter wire to any GND contact and try the red wire as in the picture.

If you have readings of about zero volts everywhere then switch the multimeter to short circuit search mode and measure again at the same points. If at least somewhere there is a short circuit you need to resolder this chip.

After you have resoldered the chip, check the board without a chip for a short circuit on these contacts. Also on a broken stand alone chip most likely these contacts will have a short circuit.

Before soldering a new chip, protect the display port with a metal plate for example with cans so that the plastic does not float. Put a few coins on the processor so that they take heat from the hot air rework station so as not to unsolder. Attach the Raspberry Pi to the wooden board with two pins for convenience.

Take a photo of the components if in case of carelessness you move a capacitor so that you can solder it back in place.

Unsoldering a broken chip requires about 350 degrees Celsius. To solder a new chip requires no more than the melting point of tin, about 290 degrees Celsius. Try not to overheat the chip as it may burn out. After soldering the chip, let it cool down and check the contacts again for a short circuit (in those places pointed to by the arrows in the picture). If there is no short circuit, try turning on the 5 volt power supply.

If the micro SD card is pulled out and you see that the green light has started to blink or glow, it means that some contact on the chip is not soldered. You can solder this contact with a soldering iron. Check for a short circuit again and try to turn it on again. If only the red LED is lit, try measuring the volts. If all the volts have appeared then most likely you have repaired your Raspberry Pi.

If you can resolder this chip yourself, you will get a new experience and a lot of fun. Also search on YouTube for what it looks like in practice: https://www.youtube.com/watch?v=Hunm5S94BaE (you can include auto subtitles in another language)

Answer 2

I did the exact same thing: Shortened the 5V and 3V3 rail by accident (with a probe).

In my case it was sufficient to replace the Power-Management-Chip, which is indeed available. I used aliexpress to order it (MXL7704-R3).

You will however need a hot air rework station. A cheap one as in my case will do, but a simple hot air blower from the hardware store is not sufficient (as it is too hot and too coarse). Of course, some soldering skill is required.

Please try this repair :) In the worst case you will loose 5 bucks but earn some experience. In the best case, your RPi3B+ is alive an well again for only 5 bucks.

Answer 3

It is very well possible to repair this. The schematics for the board are available on the raspberry pi website and you can get the one for your model. Depending on your model, you may or may not have a fuse that links the fried components together. If the components did not have fuses, you will have to buy new ICs and solder them on weather thats a whole new CPU or a power management controller. The schematic is very detailed and will tell you resistance and how much voltage goes through each component. If you are not good at soldering tiny components, you are better off just buying a new one. This thing most likely wouldn't be salvageable unless you do lots of PCB work in which case a couple resistors could be of use but the rest should be recycled.

Answer 4

From Millways's answer:

replacement is infeasible

That is not true. This thread, Don't try this at home, kids!, has someone that replaced, and reprogrammed, it successfully. Also there is a YouTube video on this repair.

I tried it, after buying five MxL7704-r3, but I am a novice on using the hot air station. Finally I got one soldered in the correct place, but vdd-core is 0v and that goes to the SOC, so I quit on this.