Oh well, today I bought a dead Raspberry Pi 4B 8GB for repair.
I checked 3V3 at the post office and found low resistance - surely a dead PMIC I thought and was too lazy to check the coils around it. Turned out to be a dead CPU.
At first I got a bit upset, but then I remembered that I wanted to try replacing a CPU on a Pi for a while.
So I did. Turns out it's not that big of a deal. Though I did it twice - here's why... —>
—> I surprisingly easily reballed and soldered the first CPU, Pi started, but won't boot - signaled 4-7 with a green LED (Power failure type B - no idea what that really means).
Then I looked closer and discovered that a new chip looks a little different from a font/marking standpoint than the original shorted one I removed.
So I had to take a similar chip from a donor, reball and solder - turned out pretty well.
Maybe this incompatibility is related to DA9090/MXL7704-P4 PMIC choice 🤔.
I looked further and found at least 3-4 different CPU chips on different versions of Raspberry Pi 4B 🤯.
Interestingly enough all those I have as donors with a known blown CPU are same as the blown one above - 04E-86 N3 W 🤔.
One more. This Pi got so hot it left melt marks on the enclosure 🤯. Eventually CPU died.
It was one with MXL7704-P4 PMIC so that CPU I tried to install earlier worked perfectly fine.
So indeed it seems like different CPU chips are meant to work with different PMICs.
P.S.: It amazes me how these days reballing and replacing a CPU feels like a quick and easy job - something that was unthinkable just a few months ago 🙆♂️.
#electronics #repair #raspberrypi #electronicsrepair #microsoldering
Also had to replace that PMIC because it was dead too. And replace a thermal pad - the one customer had was too worn out and kinda asked for a substitute 😃.
Here it is in its original enclosure and full glory ✅.
@iFixit thanks a lot 😇.
Really appreciate it from you because it was you guys who inspired me to dive into repairs back in a day 🙌🏻
in_symathy
iFixit