Customer:
I have a problem with both Raspberry Pis. I’ll describe what I’ve tried and I’m attaching a picture of what’s shown on screen. I connected it to a TV. It’s a bit blurry and looks like a video card test image to me.
First I tried with one SD card, then another I bought today. Both are 16GB SDHC. Then I tried changing the installation, NOOBS and Raspbian image, of course with both cards. I also tried a full format of the SD cards. I downloaded the programs for formatting and copying images from links on raspberry.org. In the end none of that helped, so I thought something was wrong with the SD cards, although I can read them fine on the computer. Then I bought an SD card with NOOBS lite pre-installed from a local shop, thinking it would be original. And that’s it. Now I have no more ideas what to try, and even less where I could have gone wrong. Looking at the video on raspberry.org it can’t be simpler, yet it seems odd to me that both Pis behave the same way. Oh, and I tried replacing the HDMI cable, I took one from a PS4, but it’s the same again. This picture I sent appears for a few seconds and then the screen goes dark. After a few seconds it appears again and so on in a loop. The green light on the Pi flashes a little then goes out and the red one comes on, which doesn’t flash. Then the red goes out and the green starts flashing a little again and so on in a loop.
Keyboard and mouse show no signs of life, but I’m not too surprised by that since I expect their LEDs would only turn on after boot. Interestingly, the TV recognizes it as a Raspberry Pi but it doesn’t seem to boot.
Do you have any ideas?
Attachment omitted in migration: WP_20171006_18_11_09_Pro.jpg
Originally submitted via the contact form on soldered.com on 3 October 2017. Migrated to the forum for community visibility.
Soldered Support:
I’ve seen this somewhere online but can’t remember what exactly the problem is. Let me test it myself and get back to you.
Can you try using a different power supply in the meantime?
Customer:
It looks like it’s related to the power supply. I tried the other power supply from the package and with it at least it starts the installation but resets after installing about 26 MB, on both Pis the same. I also tried the step-down module which should give 3A, and I connected it to a 10A/12V power supply that I normally use to charge Li-Po batteries, but it behaves like that first power supply. I also tried a 12V lead-acid battery instead of the power supply but the same thing. Rainbow image and then reset and so on in a loop. I read on some forums that power supply problems can happen, so I was surprised when I tried the step-down module. I would take an original Pi power supply but now I’m not sure if that’s just the cause when the step-down gives 3A.
Soldered Support:
Maybe the step-down module lacks capacitance on the output - it can’t withstand the “peaks” of large currents, so the voltage drops and the Raspberry Pi shuts down. Maybe it could help to add a few capacitors, like 47uF, 100uF.
As I said, I’ll test it too and get back to you!
Customer:
You guessed right that the power supply was the issue. After none of my combinations worked, the only thing left was to try a phone charger, which honestly I didn’t expect to work at all because according to its markings it can only provide 750mA. According to Raspberry Pi documentation the power supply should not be weaker than 1.2A. And lo and behold, it works like a charm. I read somewhere on the Pi forum that in newer versions the red LED is connected to a voltage monitoring circuit, not directly, and it shouldn’t blink at all. If it blinks, too much voltage drop occurred and it usually leads to a reset. In all my combinations it blinked and often. With the phone charger it happens that it turns off briefly, but very briefly, and the Pi continues to work. At that moment a lightning bolt symbol also appears in the top right corner of the screen, which probably symbolizes power problems but not ones that would reset the Pi. True, it did restart once or twice with this power supply too, but it doesn’t matter, now I know what the problem is. I did try adding 100uF to the step-down module but it didn’t help, not one bit. I don’t know how I’d explain that 750mA works well. It doesn’t have much power but it’s presumably constant and doesn’t have big oscillations. I tried both Pis and both work great. I was pleasantly surprised. I roughly knew what I should get but still it was a pleasant surprise. Ideas are already spinning in my head about how to connect the Pi and Croduino, or even better NOVA since they’re at the same voltage level. That could be a brutal combination.
Now that I’ve solved the power supply, I have one more detail that confuses me. It’s about the T-breakout GPIO cable. One end of the cable fits nicely into the T-breakout connector, but the other end which should go to the Pi is too narrow, meaning it doesn’t have 40 pins. Do I need another adapter or something else?
Soldered Support:
Everything you wrote makes sense. Only that, of course, we don’t figure everything out in time 
I can only not understand why this switching buck converter can’t deliver enough current. It runs at a high enough frequency, has a large enough inductor… hmm, it would be worth connecting it to an oscilloscope one afternoon to see what the problem is
I have a Pi connected to USB power from a TV (which is certainly not more than 500mA) which works as an IPTV and home center and always has the lightning bolt symbol in the top right corner but it’s never turned off.
Yes, the Pi and NOVA should be simple to connect via UART or I2C… or via MQTT?
Yes, it’s narrower because it’s designed for Raspberry Pi 2 or 1, not the 3. My apologies. My mistake. Those had 13x2 GPIO header, and the 3 has 20x2. 
Can you manage by connecting with individual wires?