RPI 3 nousb

If the PI thinks the volts is too low it will normally put up a small square rainbow icon in the top right corner of the screen. Are you getting this ??

The first picture show the load of my pi 3 with touch screen and no usb or Ethernet hooked up. And the rainbow colored square showed up during this test.

This was a quick test I did right after I got home from work so I may not be thinking clearly.So...now what else should I test?

BTW that was a usb 2.1amp battery pack.

I tested my power supplies they all ranged from 4.98-5.12 volts and I was still getting the rainbow square in upper right corner. I also found out that rebooting doesn't work when attached to the touch screen, shutting down and removing power is what it takes for updates to work.

I checked 5v at the gpio header and found that I had 3.8 volts coming out of the lcd powering the pi.

Next I'll test the pi 3 with a monitor and maybe test my other pi's with the touch screen.

Glad to hear that my hunch at what was wrong was correct. :-) 

Your "3.8V" measurement clearly indicates that your pi is not getting enough power.

The rainbow square is clear indication that your pi is not getting enough power.

Now there is only one "odd" measurement: You claim to have measured 4.98-5.12V on the power supplies. My guess is that you measured that without any load. Once the pi is connected, the voltage drops. With good power supplies only a little, with a bad power supply it might be a lot. Or you measured at the power supply side of the cable, and not at the pi-side of the cable. Actually measuring at the GPIO is a reasonable way of going about measuring the power supply voltage "under load of a pi". So IMHO the 3.8V is authoritative: there is something wrong with your power supply.

And again: Double check the cable. For a lot of applications you can get away with very thin conductors in an USB cable. So many cables are manufactured with the cheapest/thinnest wires they can find. Those are not suitable for powering a 'pi.

rew

You are correct. I will add, I bet the current is the key and is less than 2A. He should check the output rating on the device. It may be only 500 mA.

Clem

The psu's I use for my pi's are 2.1amp. The voltage drop was from bad cables. I found one good cable that only dropped 0.05 volt. I also figured out that if voltage drops lower than 4.98 volts the usb ports shut off and don't work even if the voltage increases after the drop.

I'm going to retest the pi 3 and lcd once my pi B is done reinstalling with the good cable. It's running at 428 mA while downloading.

Testing the pi 3 with a monitor with what I thought was a good cable that worked with my other pi's dose not work with the pi 3.

Voltage at the psu was 5.12 volts while voltage at the 5v on the gpoi was dropping down to 4.90 volts which is of course enough of a drop to kill the usb.

My logitech wireless keyboard works with the others pi's with no problems.

Testing the pi 3 with a monitor with what I thought was a good cable that worked with my other pi's dose not work with the pi 3.

Voltage at the psu was 5.12 volts while voltage at the 5v on the gpoi was dropping down to 4.90 volts which is of course enough of a drop to kill the usb.

My logitech wireless keyboard works with the others pi's with no problems.

The Pi 3 was designed with a new power regulator. Wonder if this is a factor?

Clem