Help Troubleshooting Custom T3.5 using 100 pin LQFP Package??

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Electric Potato

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Hey guys,

I'm troubleshooting a custom T3.5 that uses the 100-pin LQFP variant of the MCU (MK64FX512VLQ12) instead of the 144 MAPBGA.
Everything looks good but my computer won't respond to the board. :(
My only lead I have is that the bootloader pins connected to Reset_B on the MCU are always reading .08V, which I'm pretty sure is incorrect because on the working custom T3.2's I have, those pins always read 3.3V.

I've checked all my connections pretty extensively, verified 5V/3.3V/GND/USB are connected correctly, and also removed the bootloader and stuck it into a working T3.2 custom board, and that board worked fine so I know I didn't fry the bootloader or something like that.

I attached my schematic in case anybody could do me the huge favor of taking a quick look; it's mostly the same as Pauls T3.5
just without the pins that don't exist on the 100pin package. I also left off the dual schottky and added a voltage divider
into A10 for monitoring battery voltage but I think that's it.

The layout I used for the board is very similar to what I used in my T3.2 builds, which all have worked fine, and touchier things like crystal layout are identical to what I used for those boards.

Anyway thanks for any ideas!

T3.5CustomSchematic.jpg
 
I don't see a crystal on the RTC. On Teensy 3.5 / 3.6 it's included on the board - I wonder if the startup code should be edited for it?
 
You know I was just kind of assuming that crystal was included on the T3.5/3.6 since there was space for it, but that it was ultimately optional, guess I shoulda made sure of that beforehand...
 
You know I was just kind of assuming that crystal was included on the T3.5/3.6 since there was space for it, but that it was ultimately optional, guess I shoulda made sure of that beforehand...

I could be wrong, it's been a few years since I messed around with the Teensy 3.6 startup code, just one of the things that is sticking out at me on a quick glance.
 
hey thanks jon yes I have, someone described seeing low voltage on the reset pin of the mkl02 but it seemed like the answer in that thread was that the mkl02 was blank, if I understood it correctly.
 
Also I'm not sure why, but if I short the MKL02 reset pads to ground with my voltage probe touching RESET_B, it goes from .08 to 0, and then when I unshort it jumps to 3.3V and stays there, but only as long as I keep the voltage probe touching. If I lift the probe off of RESET_B and then touch it back to RESET_B, it again reads .08 V. I'd guess that's the voltage meter's doing so it may not be a helpful bit of information
 
Okay I figured it out...friggin VOUT33 was weakly connected and I guess when I probed it the first time I put some pressure on it that made it register as connected to the 3.3V line, but after removing the probe it sprung back up a tiny bit to be unconnected again. I reflowed that side with a bit more paste and now everything works great.
Thank you for helping me in this time of flailing :)
 
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