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Boot loop if not using a proper USB cable
#1
Hi,
I have my Tinkerboard since some weeks and did some testing. Some days ago I set the keyboard layout to German and rebooted - and got stuck in a boot loop.
I then flashed the SD card again and had the same problem again - booting up, some weird kernel messages appear - reboot. No desktop was showing.

I then changed the USB cable I was powering the board and voila - it is now working again! I did some cross checks and really: when I use a 5 Meter micro USB cable (from Amazon, but a good quality one), I get the boot loop. When I use my old Nokia microUSB cable, it boots up.

Just wanted to share this, in case you also get stuck.

Edit: I checked the faulty cable with a Raspi 3 and the "too less power" icon appeared on the screen. I powered Raspis with this cable before, so this is a little weird. Maybe it is too long for the whole 2.5A of the power supply.
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#2
The problem is called Micro USB and unfortunately ASUS made the same mistake as other SBC manufacturers already. This crappy connector is simply not able to power anything that needs more than a few hundred mA. This is well known since RPi foundation started with this idea 5 years ago.

More details (cable resistance and encouraging users to use 'chargers' instead of PSUs) can be found in #5 and #7 here: http://tinkerboarding.co.uk/forum/showth...d=33#pid33

This forum will be soon flooded with posts like yours, we can only hope that ASUS will overthink their mistake and use a sane barrel plug solution on next PCB revision.
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#3
Thanks for pointing this out, I haven't seen the other thread in this forum. My main initial confusion came from the fact, that the cable worked at first and failed later. Maybe I moved the device somehow... who knows.
I absolutely agree, that the microUSB connectors are not very reliable and would also wish a proper industry-like solution.
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#4
(02-28-2017, 08:07 AM)KokoMcNeal Wrote: My main initial confusion came from the fact, that the cable worked at first and failed later.

You're talking about a 5m cable. Under best conditions (very very low resistance, AWG20 rating) this could work with very light consumption behaviour. Please see 'Ohm's law' and scroll down to the tables which show cable resistance, cable length and expected voltage drop based on consumption: http://goughlui.com/2014/10/01/usb-cable...ging-slow/

Most users unfortunately don't even know what Ohm's law is and how average USB cables affect instability problems. The more the board consumes (load peaks or connecting USB peripherals or an LCD with an own backlight) the higher the voltage drop. So while a bad cable might seem to work your board gets in trouble as soon as you connect stuff or let anything heavy run.

Then it gets even worse since sudden reboots or unsafe shutdown can add to filesystem corruption on the SD cards and then even if you fix your power supply situation you will still run in instabilities since now your installation is broken.

All this is well known since at least 4.5 years (a few months after RPi launch it was already obvious what a shitty idea Micro USB is for DC-IN) so I was really surprised to see ASUS repeating this mistake again.

Let's hope the moderators here are smart, use all the links collected here and assemble a simple FAQ pointing at that reason N° 1 for any 'instability' is powering Tinkerboard the usual (read as: wrong) way.
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#5
"All micro USB cables are not equal" - they vary greatly in resistance, and it's not something you notice in general use until using it to power a Tinkerboard or raspberry Pi.

Basically higher resistance means using the same 2A PSU, one cable might give 2A - the other as low as 0.5A,
and this will cause the tinkerboard to be unstable, or not work at all.

When used to charge your phone, you'd only notice a lower charge rate.

Cables can "go bad" if stranded wires inside break, and some use the more brittle CCA (copper clad aluminium) instead of copper

So what's an easy way to test them ?

Well what I do is plug them into a 2A PSU and my android phone.
Then use the free android app "Galaxy charging current"
https://play.google.com/store/apps/detai...e&hl=en_GB

Here's good and bad micro usb cables:

[Image: 0bxoWjum.png] [Image: c5dMYGMm.png]



Ironically the 2nd cable above was quite a bit thicker - so you really need to test rather than just go on visual appearance.
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#6
If anyone is interested, here is how I test my cables with a Raspi now:
I have a Pimoroni Blinkt! (8 RGB LED bar) connected to each of my Raspis and noticed when I have 100% at all 4 cores and the LEDs on, the cheap cables fail.
(= the voltage warning comes on the screen)

There is an example called "rainbow.py" coming with the Blinkt! hardware which cycles all LEDs through the spectrum. When you start this more times (8x for example) the LEDs go mad and all cores are at 100%. I did this with all cables on all Raspis in the cluster and sorted out the bad cables.
I bought some Anker PowerLine+ cables for a replacement and ALL of these work.

Link to Blinkt!:
https://shop.pimoroni.com/products/blinkt
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#7
(03-05-2017, 11:55 AM)Mikerr Wrote: "Basically higher resistance means using the same 2A PSU, one cable might give 2A - the other as low as 0.5A

Nope Smile

Your conclusions/recommendations are correct but the explanation above isn't. The reason why average USB cables suck has been explained before (have to deal with just 500 mA maximum current due to USB2 specs), the technical detail involved is Ohm's law and the real problem when it's about the cable is undervoltage and not undercurrent (that's then not a cable but a PSU problem, the average cheap 2.5A PSU not capable to provide more than 1.5A at 4.8V or above).

Smartphones contain always a PMIC (power management IC) that does some measurements (voltage, current, temperatures when the battery has a high capacity) and then act on environmental conditions. When the PMIC realizes a huge voltage drop it lowers charging current to prevent damage (cable and contact resistance do not only lead to lower voltage but due to Ohm's law the 'wasted energy' will be emitted as heat, so what your phone simply does is preventing things catching fire!).

BTW: If you need more than one such a good USB cable just enter '20awg micro usb' in Amazon's search box, check reviews and order (AWG == american wire gauge). There are sets with 5 cables for approx. 10 bucks available.
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#8
I actually thought I had a crappy product before I tested with different USB cables. Mine just randomly shut off or rebooted while trying to do stuff that put load on the CPU. The cable I was using was by the looks of it pretty beefy, but opening it up to check it was pretty thin. So make sure to read on the cable, that it really is a 20-26 AWG cable.

I've also tried to use the official RPi supply (5.1v 2.5A), but it has 18 AWG cable. I get random crashes in X when using that. So I'm using a 5.x v 3.1A supply with a 26AWG cable and stable as a rock so far. So don't cheap out on cables, or supplies!
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#9
(03-29-2017, 02:24 PM)pocketlight Wrote: I've also tried to use the official RPi supply (5.1v 2.5A), but it has 18 AWG cable. I get random crashes in X when using that. So I'm using a 5.x v 3.1A supply with a 26AWG cable and stable as a rock so far. So don't cheap out on cables, or supplies!

BTW: the lower the AWG rating the better the cable should be (since lower ratings correlate with thicker cable diameters). But just like everywhere else... if you buy really cheap you get fakes and cables that are rated 18AWG are thin 26AWG in reality!

http://nerdralph.blogspot.de/2016/06/whe...ables.html
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#10
Just a little side note, not all chargers/PSUs are equally designed either, just have a look at this one here and the voltage diagram at different loads;

https://techtest.org/aukey-pa-t16-quick-...s-im-test/
https://techtest.org/wp-content/uploads/...agramm.jpg

I'm currently using this one for the TB without any issues at all...

//Per
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