Raspberry Pi 3B+ 3.3v short to ground - Page 1
Forum section: electronics / repair

author: Mamejay
author_rank: Contributor
timestamp: July 21, 2018, 04:33:16 am
content: Hi everyone,I have a Raspberry Pi 3B+ which looks to have 3.3v shorted to ground.This was a brand new unit which I was using for about 30 minutes. Switch it off and the next day tried to fire it back up again and it would not boot. Power LED comes on but that's it.I did not connect anything strange to the GPIO's so not sure what is happening. Anyway further investigation shows 3.3v is shorted to ground.From my reading the MXL7704-R3 chip does the voltage regulation on the 3B+. What I want to do is isolate the 3.3v easily to see which direction the 3.3v is shorted without removing the MXL7704-R3.Is there any trace or passive component I can remove/cut to isolate it?I did receive these for free with a offer from arrow.com so I am not too upset about it but would like to try and get this going. Or at least work out what failed.Any help would be great. thanks

author: mubes
author_rank: Regular Contributor
timestamp: July 21, 2018, 07:20:01 am
content: Blast it with freezer spray until ice forms and you'll quickly see where the 3v3 is running to ground because it'll melt quickly there. Wait for the condensation to evaporate before working further on the board though!

author: shved
author_rank: Regular Contributor
timestamp: February 22, 2020, 08:00:03 pm
content: Same problem here. Friend gave me a brocken PI 3 +. Something on 3v3 is internally shorted. Is there a way to find what it is without sucking the chips out & cutting the traces?

author: RoGeorge
author_rank: Super Contributor
timestamp: February 22, 2020, 08:19:35 pm
content: The first I will suspect will be any capacitors between the shorted +3.3v and GND.RPi has available schematics, so it should be possible to identify them all. Start with the MLCC ones. A layer of isopropyl alcohol might work, too, to show which one of the suspected capacitors to check first.

author: shved
author_rank: Regular Contributor
timestamp: February 22, 2020, 09:24:32 pm
content: Found it, it is the XR77004 power chip.As it is a lost cause and friend already bought a new one i ll try to power the board from external regulators. But there are quite a lot of rails: 3v3, 1v8, 1v2. I don't know how practical it would be, but it's worth a shot, It is a spare PI for not critical tasks, if it survived whatever fried the power chip. Tomorrow i'll cut out shorting bit, rig-up 3 lab PSU's and let'er rip.

author: shved
author_rank: Regular Contributor
timestamp: February 23, 2020, 05:24:39 pm
content: Yep, I've seen that. But before ordering a new chip, i would like to manually power the rails.Is there a problem with doing something like this(sequence, etc.)?

author: shved
author_rank: Regular Contributor
timestamp: February 23, 2020, 07:54:30 pm
content: Now i'm powering the pi from 3 external regulators: 3v3, 1v8 and 1v2.I have some progress: now pi is trying to boot.The symptoms without SD card: solid red power ledThe symptoms without SD card: solid red power led & green blink code for witch i can't find any description. Te pattern is - 5 long & 7 short blinks.Any advise on where to dig next?

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: February 23, 2020, 08:16:56 pm
content: My advice: buy an Orange Pi PC ($15) install Armbian and forget the raspberries...

author: shved
author_rank: Regular Contributor
timestamp: February 23, 2020, 08:26:16 pm
content: Thanks, I've already got one, an older version PC plus(if memory serves). I'm not one for throwing fixable stuff out and have some free time this afternoon.So, if anyone has some suggestions - i'm all ears.

author: shved
author_rank: Regular Contributor
timestamp: February 24, 2020, 12:54:28 pm
content: Is there full schematics for PI 3 B+ release?I could't find it, only the simplified version.

author: shved
author_rank: Regular Contributor
timestamp: February 26, 2020, 06:34:00 pm
content: I think the code is "Power failure type B".(https://www.raspberrypi.org/documentation/configuration/led_blink_warnings.md)But i don't know WTF is it. I've got power on all the rails, everything that was shorted is sucked out. No idea on what to do next.Anyway, the only schematics I've found is (https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/rpi_SCH_3bplus_1p0_reduced.pdf). I'm giving up for now.

author: wraper
author_rank: Unknown
timestamp: February 26, 2020, 06:57:43 pm
content: Quote from: RoGeorge on February 22, 2020, 08:19:35 pmAfter repairing many hundreds of different raspberry Pi, The only capacitor to ever fail was 47uF MLCC near mounting hole (C97 for VUSB). I repaired only up to 3B. 3B+ has different set of ICs but I would expect that probably LAN/USB chip failed. Or might be CPU itself.

author: KaneTW
author_rank: Frequent Contributor
timestamp: February 26, 2020, 06:58:59 pm
content: The PMIC on the Raspberry Pi 3 is a custom IC I believe. You can get a similar IC but it has slight differences.

author: wraper
author_rank: Unknown
timestamp: February 26, 2020, 07:03:04 pm
content: Quote from: KaneTW on February 26, 2020, 06:58:59 pmIt's not a custom IC (what for?) and has marking of off the shelf PMIC.Edit: it probably is since Pi3 has it with R3 suffix but Pi4 with P4 suffix. But you can easily buy them on aliexpress, though.

author: wraper
author_rank: Unknown
timestamp: February 26, 2020, 07:19:03 pm
content: Quote from: Mamejay on July 21, 2018, 04:33:16 amReturn it. Receiving it as offer, does not mean it has no warranty. You did not receive it for free BTW, it was included in the price. And IMHO chances repairing it are slim without having any donor boards to salvage replacement ICs.

author: KaneTW
author_rank: Frequent Contributor
timestamp: February 26, 2020, 09:40:54 pm
content: Quote from: wraper on February 26, 2020, 07:03:04 pmI haven't looked at Ali but the manufacturer didn't have them for sale and there was some article about how it's a custom IC etc.

author: wraper
author_rank: Unknown
timestamp: February 26, 2020, 10:07:36 pm
content: Quote from: KaneTW on February 26, 2020, 09:40:54 pmIf it's custom, it's nothing than with what initial settings it's programmed at the factory. In the datasheet you can find:Quote

author: KaneTW
author_rank: Frequent Contributor
timestamp: February 26, 2020, 10:55:35 pm
content: Yeah, it's just preprogrammed settings or a slightly different pinout afaik.

author: wraper
author_rank: Unknown
timestamp: February 26, 2020, 11:08:26 pm
content: Quote from: KaneTW on February 26, 2020, 10:55:35 pmPinout is the same as well as silicon.