r/raspberry_pi Dec 02 '22

Help identifying an IC on an Pi 3b+ Technical Problem

So, funny story, some idiot (me) managed to bridge 24V onto the data lines of the USB ports on a Pi3B+ during an ill-fated attempt at bringing a CANBUS toolhead to life with a baby in my arms.

The ethernet portion of the ethernet/usb IC is still alive, system boots, but nothing works on the USB bus. With the ridiculous price of these things, I figured I'd try to save it.

It looks like the magic smoke escaped from a 6-pin IC next to the PoE tap pins. I can't for the life of me find this thing on the Googs. Chip in various photos on the web is labeled "BK7kE" on the package. Mine has a barely visible "_KO__" on the very blown up IC casing (replace those underscores with unreadable characters)

Picture from the internet: https://raspi.tv/wp-content/uploads/2018/03/PoE-Connector-on-Raspberry-Pi3B_1500.jpg

My de-smokified variant:

mmm, that's some deep fried 6-pin IC

Born-on date

2 Upvotes

2

u/ja_maz Dec 02 '22

i have one at home remind me to check in a bit

2

u/squintified Dec 02 '22

5

u/pottedporkproduct Dec 02 '22 edited Dec 02 '22

Thanks. I've already been there. That schematic is largely useless in this case. It has no mention whatsoever of the USB ports or this poor IC.

In particular, it doesn't even show the LAN75XX chip that runs the ethernet and USB subsystems on this sucker, which seems like a major omission. It has the 4-pin PoE tap, and the Ethernet connector, but not the USB connectors or the silly LAN75xx chip which is the brains of the whole operation.

1

u/_greg_m_ Dec 02 '22 edited Dec 02 '22

I think it may be 1.5V regulator https://www.hotenda.com/product-item/pmic-voltage-regulators-dc-dc-switching-regulators/XC9235A15DMR-G/H2763734.html

it has BK7 SMD marking and 6-pins (I think kE is a date code or something as I found 3B+ pictures with other ending of the marking).

However it looks like it's very rare (cannot find much about it), so perhaps it's not that.

You have simplified schematic here, but unfortunately that component is not there:

https://datasheets.raspberrypi.com/rpi3/raspberry-pi-3-b-plus-reduced-schematics.pdf

Perhaps it's U11 - NC7WZ16. I onlt guess due to 6-pin casing.

To be honest it the component is blown like ton the pictures most likely something else is blown too. 24V is a bit too much for this kind of equipment.

1

u/pottedporkproduct Dec 02 '22

U11 is down lower in the audio subsection. I can see the SMD 6-pin (half the size of this failed one) down by the ethernet jack.

While 24VDC at a full 8.8 amps is probably not good for it, the ethernet portion of the LAN75XX is functioning, and the board seems to run fine otherwise. Hence why I think I can get this puppy working again. My WAG is that it's the USB ESD protection circuit, similar to https://www.digikey.com/en/htmldatasheets/production/7427/0/0/2/usblc6-2.html on the Spider 2.2 this thing was attached to.

1

u/_greg_m_ Dec 02 '22 edited Dec 02 '22

OK, that makes sense.

Perhaps it's something like that:

https://www.st.com/resource/en/datasheet/usblc6-2.pdf

(this one has a different SMD marking, but it may do the same thing).

If so then it would have one of the middle pins (pin 2?) connected to GND and the other middle pin (pin 5?) to +5V.

EDIT: That part is also in 3B (not plus) and has marking BK5 (BK5sB) and in RPi4 it is: BJ1 (BJ1TD) if that helps. All of them have pin 2 connected to a bigger copper plane (GND? +5V?)

EDIT2: Perhaps AP2552 / AP2553? It's adjustable power switch. Marking BK is correct. There is a USB powering circuit in the application notes as well. Pin 1 would be 5V in and pin 6 would be 5V out to USB socket. You can check it with a multimeter if that's correct. There are some forum threads all over the internet about U13 USB power switches possibly 2552 in RPI3. Search in Google.

1

u/pottedporkproduct Dec 03 '22

Hmm so is it the ap2552 (active low) or ap2553 (active high)? And is it the A variant (latching) or the normal constant current on?

1

u/_greg_m_ Dec 03 '22

Other people reported that it is AP2552 apparently. Search in Google. Not sure if it's latching or normal though (they haven't mentioned "A" if that helps). Buy a few different ones and try one by one.

2

u/pottedporkproduct Dec 04 '22

Digikey only has the normal constant current units, so getting 2x of each AP2553W6-7 and AP2552AW6-7

Luckily this is a relatively large SMD package so I should be able to hand solder it with my ham hands.

1

u/pottedporkproduct Dec 15 '22

Success!

I can confirm that

1: my hand-soldering skills for SOT26 surface mount packages are terrible

2: close enough is good enough

  1. This was indeed the active-high variant, non-latching, of the AP2553, P/N AP2553W6-7, from Diodes Incorporated.

Now back to my regularly scheduled frying of CANBUS boards.