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3B+ suddenly died with no video out and solid act led

Posted: Mon Jul 29, 2019 11:46 am
by ModernWires
My 3B+ suddenly stopped working yesterday. When I power it on I get two solid leds and they just stay on forever without blinking or anything. I checked the sticky thread but it didn't seem to cover the case where the act led doesn't blink at all. I guess it means the pi can't read from the micro sd card so I tried another card with a fresh copy of the latest raspbian but it still didn't work. I checked the voltage on the 5v and the 3.3v pins and they all read correctly unlike in some cases where the 3.3v rail is fried.
I have no idea what happened to my pi. I preordered a new pi 4b but it won't arrive any time soon.

Please help! I don't want to give up if there's still one thing I can do to fix my pi.

Re: 3B+ suddenly died with no video out and solid act led

Posted: Mon Jul 29, 2019 12:00 pm
by DougieLawson
Pull the SDCard. Power on. Does it do the same thing? Does any part of your RPi get too hot to touch very quickly? Have you been abusing GPIO pins?

Can you measure the voltage between Pin#1 & GND (use the case of the USB or ethernet to avoid shorting pins)? Can you do the same for Pin#2 (or Pin#4)?

You may have had the spontaneous sudden death of your PMIC chip - the repair costs £35, but you'll get the bonus of an upgrade from RPi3B+ to RPi4B1GB for that price.

Re: 3B+ suddenly died with no video out and solid act led

Posted: Mon Jul 29, 2019 1:08 pm
by ModernWires
DougieLawson wrote:
Mon Jul 29, 2019 12:00 pm
Pull the SDCard. Power on. Does it do the same thing? Does any part of your RPi get too hot to touch very quickly? Have you been abusing GPIO pins?

Can you measure the voltage between Pin#1 & GND (use the case of the USB or ethernet to avoid shorting pins)? Can you do the same for Pin#2 (or Pin#4)?

You may have had the spontaneous sudden death of your PMIC chip - the repair costs £35, but you'll get the bonus of an upgrade from RPi3B+ to RPi4B1GB for that price.
I tried powering it on without the sd card and I got a single solid red pwr led.
I measured the voltages of all the power pins (pin 1,2,4,17) and they were perfectly fine. (3.3v on pin 1 and 17, 5v on pin 2 and 4)

I previously connected a led and a buzzer and everything worked just fine until I tried to boot it up yesterday.

Re: 3B+ suddenly died with no video out and solid act led

Posted: Mon Jul 29, 2019 2:21 pm
by HypnoToad
What voltage do you get if you measure between GND and PP9?

Re: 3B+ suddenly died with no video out and solid act led

Posted: Mon Jul 29, 2019 5:50 pm
by Burngate
ModernWires wrote:
Mon Jul 29, 2019 1:08 pm
I previously connected a led and a buzzer and everything worked just fine until I tried to boot it up yesterday.
How did you connect those?
Taking too much current from a GPIO, or letting more than 3v3 near a GPIO can damage the SoC

https://www.raspberrypi.org/forums/view ... 28&t=58151 is useful, if you haven't already read it.

Re: 3B+ suddenly died with no video out and solid act led

Posted: Tue Jul 30, 2019 4:14 am
by ModernWires
HypnoToad wrote:
Mon Jul 29, 2019 2:21 pm
What voltage do you get if you measure between GND and PP9?
I got 1.8v.

Re: 3B+ suddenly died with no video out and solid act led

Posted: Tue Jul 30, 2019 4:24 am
by ModernWires
Burngate wrote:
Mon Jul 29, 2019 5:50 pm
ModernWires wrote:
Mon Jul 29, 2019 1:08 pm
I previously connected a led and a buzzer and everything worked just fine until I tried to boot it up yesterday.
How did you connect those?
Taking too much current from a GPIO, or letting more than 3v3 near a GPIO can damage the SoC

https://www.raspberrypi.org/forums/view ... 28&t=58151 is useful, if you haven't already read it.
GPIO -> Led +
GND -> Led -

3V3 -> Buzzer VCC
GND -> Buzzer GND
GPIO -> Buzzer Input

Re: 3B+ suddenly died with no video out and solid act led

Posted: Tue Jul 30, 2019 9:08 am
by Burngate
ModernWires wrote:
Tue Jul 30, 2019 4:24 am
GPIO -> Led +
GND -> Led -
You need a resistor between the GPIO and the LED (or between the LED and GND) to limit the current.
Too much current can damage the GPIO circuitry inside the SoC, and that damage can spread.

LEDs are not straight-forward devices - up to a certain voltage, almost no current passes, but above that voltage they act like very low resistances, so very large currents can pass.

This may be the cause of your problem - or it may not, depending on the actual current your particular LED took
3V3 -> Buzzer VCC
GND -> Buzzer GND
GPIO -> Buzzer Input

Re: 3B+ suddenly died with no video out and solid act led

Posted: Tue Jul 30, 2019 3:01 pm
by ModernWires
Burngate wrote:
Tue Jul 30, 2019 9:08 am
You need a resistor between the GPIO and the LED (or between the LED and GND) to limit the current.
Too much current can damage the GPIO circuitry inside the SoC, and that damage can spread.

LEDs are not straight-forward devices - up to a certain voltage, almost no current passes, but above that voltage they act like very low resistances, so very large currents can pass.

This may be the cause of your problem - or it may not, depending on the actual current your particular LED took
Well RIP my raspberry pi. I did put a 51Ω resistor in the circuit. I guess that's not enough to limit the current to a safe level.
The LED didn't seem to be overly bright or anything so I thought it was fine and it did seem to work for a couple of days without any obvious sign of problems.

Re: 3B+ suddenly died with no video out and solid act led

Posted: Tue Jul 30, 2019 5:59 pm
by Burngate
ModernWires wrote:
Tue Jul 30, 2019 3:01 pm
I did put a 51Ω resistor in the circuit. I guess that's not enough to limit the current to a safe level.
A GPIO can safely provide 16mA.
16mA through 51Ω would mean about 0.8v across it, so the LED would have to have 2.5v across it.

There's a nice graph in Kingbright's spec. sheet for their L9341 high efficiency red LED
Red LED I-V.png
Red LED I-V.png (6.13 KiB) Viewed 311 times
As you can see, 16mA through the LED requires about 2v across it, so the resistor has to drop 1.3v, so 100Ω or more

(Nice to see the use of the omega symbol - most people seem to use R instead, probably because their ordinary keyboard can't do Greek and they can't be bothered to do the job properly.
You'll probably observe that I've used lower-case v for Volts instead of capital V. That just means I'm as lazy as the rest of them)

Re: 3B+ suddenly died with no video out and solid act led

Posted: Sat Aug 03, 2019 1:30 pm
by ModernWires
Burngate wrote:
Tue Jul 30, 2019 5:59 pm
A GPIO can safely provide 16mA.
16mA through 51Ω would mean about 0.8v across it, so the LED would have to have 2.5v across it.
Thanks. Good to know.
I probably should use a separate power rail to power everything anyway. The buzzer is most likely also drawing over 16mA.
Maybe I can get one of those USB adapters that plugs into the breadboard.