LawnMowerMan
Posts: 2
Joined: Fri Jul 06, 2018 4:05 pm

Only 0.01V on the 3.3V pin and fails to boot

Fri Jul 06, 2018 6:02 pm

I have two new Raspberry Pi B+, one is functional the other is not.

I will call the functional PI-WORKS, the other Pi-FAILS.

They both came with the ConaKit power-supply. I will call these supply-A and supply-B.

All three SDcards will boot in PI-WORKS. Therefore all SDcards are functional.

There is no green light when attempting to boot Pi-FAILS with any SDcard.

Voltage check on 5V pin:
Pi-FAILS + supply-A 6.64V
Pi-FAILS + supply-B 6.82.V

Voltage check on 3.3V pin:
Pi-FAILS + supply-A 0.01V
Pi-FAILS + supply-B 0.01V

Voltage check on 5V pin:
PI-WORKS + supply-B 6.80V while booted, 6.94V after power-off

Voltage check on 3.3V pin:
PI-WORKS + supply-B 4.45V while booted, 4.47V after power-off
PI-WORKS + supply-A 4.52Vwhile booted, 5.54V after power-off

While the voltage tests are not exhaustive a clear trend indicates that both power-supplies are functional.

Pi-FAILS has only 0.01V on the 3.3V pin. Can anyone suggest a solution? Can I get a replacement from the manufacture? How do I go about getting a replacement?

Best regards

hippy
Posts: 3588
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Only 0.01V on the 3.3V pin and fails to boot

Fri Jul 06, 2018 6:48 pm

LawnMowerMan wrote:
Fri Jul 06, 2018 6:02 pm
I have two new Raspberry Pi B+
Do you really mean the older "Pi B+", or the newer "Pi 3B+" ?
LawnMowerMan wrote:
Fri Jul 06, 2018 6:02 pm
Voltage check on 5V pin:
Pi-FAILS + supply-A 6.64V
Pi-FAILS + supply-B 6.82.V

Voltage check on 5V pin:
PI-WORKS + supply-B 6.80V while booted, 6.94V after power-off

Voltage check on 3.3V pin:
PI-WORKS + supply-B 4.45V while booted, 4.47V after power-off
PI-WORKS + supply-A 4.52Vwhile booted, 5.54V after power-off
I can only assume you have a very uncalibrated meter as the voltages are all way above what they would be expected to be. Even if you were putting in well over 5V one wouldn't expect the regulated 3V3 to stray much from 3V3.

Not sure what you mean by "after power off", because there should be no voltage with no power supplied, but I would again presume you mean when shut down rather than unplugged.

Please correct me if I have made false assumptions because that would be important if it is how you say it is.

No matter what the true voltages are it does seem the regulated 3V3 supply has failed in some way, and that would prevent things working.

Reading 0.01V would suggest it's either at 0V, or there's an open circuit.

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rpdom
Posts: 12741
Joined: Sun May 06, 2012 5:17 am
Location: Ankh-Morpork

Re: Only 0.01V on the 3.3V pin and fails to boot

Fri Jul 06, 2018 7:20 pm

hippy wrote:
Fri Jul 06, 2018 6:48 pm
I can only assume you have a very uncalibrated meter as the voltages are all way above what they would be expected to be. Even if you were putting in well over 5V one wouldn't expect the regulated 3V3 to stray much from 3V3.
The usual cause for abnormal readings is a low battery in the meter.

LawnMowerMan
Posts: 2
Joined: Fri Jul 06, 2018 4:05 pm

Re: Only 0.01V on the 3.3V pin and fails to boot

Wed Jul 11, 2018 2:44 pm

This is the Pi 3B+.

Hippy, thanks for the battery suggestion on the volt meter. I changed the battery, here are the updated readings;

Voltage check on 5V pin:
Pi-FAILS + supply-A 5.20V

Voltage check on 3.3V pin:
Pi-FAILS + supply-A 0.00V

As you can see the 3.3V pin has no power.
Is there a specific area of the forum I should move to?

gkaiseril
Posts: 432
Joined: Mon Aug 08, 2016 9:27 pm
Location: Chicago, IL

Re: Only 0.01V on the 3.3V pin and fails to boot

Wed Jul 11, 2018 3:13 pm

Many voltages for AC mains are specified as a range for many power supplies, I would then expect any DC voltage from a DC power supply, unless regulated, to generate the DC voltage within some range.

Most electronics are tested using test points on the circuit board.Have you tested at these points?

Since you have found that weak batteries can cause measurement issues, have you also check the zeroing of you meter?

You also might want to check your 3 VDC measurement against a known 3 VDC source like 2 AA, C or D batteries.

I would visually inspect the micro USB socket and the SD card socket and look to see if there are nay misaligned, lose, or shorted connectors in the unit that is not working.

Have you considered contacted the supplier about returning the defective product?

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davidcoton
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Joined: Mon Sep 01, 2014 2:37 pm
Location: Cambridge, UK

Re: Only 0.01V on the 3.3V pin and fails to boot

Wed Jul 11, 2018 5:18 pm

gkaiseril wrote:
Wed Jul 11, 2018 3:13 pm
Many voltages for AC mains are specified as a range for many power supplies, I would then expect any DC voltage from a DC power supply, unless regulated, to generate the DC voltage within some range.
The range that the PSU will tolerate on its input is not connected to the output voltage, because any supply suitable for a Pi will be regulated.
gkaiseril wrote:
Wed Jul 11, 2018 3:13 pm
Most electronics are tested using test points on the circuit board.Have you tested at these points?
Use of the test points is a matter of convenience. It will not affect the result.
gkaiseril wrote:
Wed Jul 11, 2018 3:13 pm
You also might want to check your 3 VDC measurement against a known 3 VDC source like 2 AA, C or D batteries.
Batteries are a very poor reference, since the voltage varies considerably with the state of charge.
gkaiseril wrote:
Wed Jul 11, 2018 3:13 pm
I would visually inspect the micro USB socket and the SD card socket and look to see if there are nay misaligned, lose, or shorted connectors in the unit that is not working.
Not relevant in this case, since 5V is present on the board and 3V3 is not. (A short from 3V3 to 0V on the SDCard slot or elsewhere is just about conceivable, but should not affect a new Pi on first use.)
gkaiseril wrote:
Wed Jul 11, 2018 3:13 pm
Have you considered contacted the supplier about returning the defective product?
+1. From the information the OP gives, this sounds like a rare "dead on arrival" Pi. If, of course, the OP is sure that nothing could have damaged the Pi when it was first connected and powered on.
"Thanks for saving my life." See https://www.raspberrypi.org/forums/viewtopic.php?p=1327656#p1327656
“Raspberry Pi is a trademark of the Raspberry Pi Foundation”

hippy
Posts: 3588
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Only 0.01V on the 3.3V pin and fails to boot

Wed Jul 11, 2018 7:52 pm

The 3V3 on a Pi 3B+ is generated by the PMIC chip, as are 1V8 and some other voltages. It might be worth checking those as well. My guess is they are all down; either a PMIC issue or something causing it to not enable power output.

Contacting the supplier for return, testing, repair or replacement, would also be my recommendation.

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