Custom Teensy 3.1 PCB troubleshooting

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EK701

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I've built a custom PCB based on the Teensy 3.1 schematic from PJRC and I am using a Mini54 purchased from PJRC. On power up, it doesn't appear the Mini54 is properly communicating with the Mk20. I've read through the links on the PJRC Mini54 page and I don't appear to have any of the issues that came up there. I'm still not having any success.

Here is the schematic:

MotoDisplay 1.41 Schematic.jpg

Here is what the Reset (P3.2), in yellow, and Prog (P5.2), in blue, pins look like on the scope:

IMG_2874.jpg

Here is what happens when I ground the Prog line:

IMG_2876.jpg

Power is clean and solid.

I'm getting no USB communications. Ideas?
 
If you ground the PROG line, but the RESET line doesn't go low, the Mini54 is probably not running or hearing the PROG line.

While you continue holding PROG low, the Mini54 is supposed to keep RESET low.
 
PaulStoffregen said:
If you ground the PROG line, but the RESET line doesn't go low, the Mini54 is probably not running or hearing the PROG line.

While you continue holding PROG low, the Mini54 is supposed to keep RESET low.
Click to expand...

I saw that in one of the other threads. Pointers to where I should look for a problem are appreciated. Thanks!
 
On the Mini54 page, scroll down to "Troubleshooting". You'll find links to prior conversations about problems, which were ultimately resolved.

If your board turns out to have some other issue, and we ultimately figure out what's wrong, I'd like to ask you to post a quick followup about what ultimately caused the trouble. As you can see in those other threads, having that followup together with the conversation about how the problem appeared and what was done to diagnose it can be really helpful to others who might later have a similar issue.
 
If the Mini54 isn't pulling RESET low when you hold PROG low, first you want to get it PROG really is arriving at the Mini54 pin.

You probably want to check some other obvious stuff on the Mini54, like if it really has power, all its pins are connected, none are shorted to each other or other stuff, and so on.
 
PaulStoffregen said:
If the Mini54 isn't pulling RESET low when you hold PROG low, first you want to get it PROG really is arriving at the Mini54 pin.

You probably want to check some other obvious stuff on the Mini54, like if it really has power, all its pins are connected, none are shorted to each other or other stuff, and so on.
Click to expand...

Yep, been down that road. I'm using the 5mm QFN Mini54, so checking pins for shorts is a bit more difficult, but I don't see any shorted pins under magnification. Time to triple check everything again.

What other signals should I be seeing on the various Mini54 pins?
 
Have you tried sending a program to it?
I thought I had issues until I sent Blink to it.. USB woke up and worked.

If you just connect to USB, it will not come up until sketch is uploaded.
 
That is true.. Just it is hard to see his schematic.. I was fortunate that mine actually worked, but did not know it..
 
So I had some time today to look into this further. I put hot air to the Mini54 trying to make sure all the solder points were good, but that made no difference. I pulled the Mini54 and checked the traces to it while powered up without the Mini54 and everything appeared OK. I installed a new Mini54 with the same result. I spent well over an hour looking at various signals, and finally found the 16MHz crystal didn't appear to be working, as I was not seeing a good signal on PTA18/PTA19 of the MK20. I pulled the crystal and installed a new one. Same problem. I look at the schematic and the crystal data sheet and realize I have the pins/pads wrong in the Eagle library I created for it. Arrrgh!

Time to make new boards...
 
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