Trying to fix broken Teensy 3.6 boards -- is there a component layout guide anywhere?

[CraigF]

I'm seeking information that will help me link the schematic with the board layout.

One of my Teensy 3.6 boards arrived missing a passive component (bare pads coated with solder).

It still appears to work fine, and I assume the missing element is a capacitor, but I can't tell what value. It's the component immediately inboard of pin 20, and it's slightly turquoise colored on one of my good boards. Here's a photo of the missing component (pads just to the left of the through-hole).



I've pored over the schematic, and I'm very grateful to have it, but it's not quite enough. I've tried to trace the board, but there are so many traces that go underneath parts and so many vias that I keep making missteps. There are no markings on the passives.

Has anybody got a picture or diagram of the board layout indexed to the schematic?


Thanks!!!!!

-- Craig

 

[aFewBits]

The missing part is a 470 ohm resistor connected between VDDA and VREFH. One end (VREFH) is connected to the AREF header pin.

 

[PaulStoffregen]

analogRead() probably will not work without that resistor, unless you use analogReference(INTERNAL).

 

[CraigF]

The missing part is a 470 ohm resistor connected between VDDA and VREFH. One end (VREFH) is connected to the AREF header pin.

Got it. Thank you!!!

But please help me here: how did you know that? The traces vanish into vias and under chips, and don't connect to anything I could positively identify from the schematic. I was looking in a completely different area. Perhaps I *should* have spotted it from the relationship to the two ferrites, but really I was about to lift a few nearby passives and test them for values. What am I not seeing?

 

[aFewBits]

Elementary, my dear watson...

Powers of observation and the process of elimination. I had the advantage of seeing it was blue/aqua in color. Comparing it to similar devices on the board showed two others above and to the left of the missing part. Those went into the BGA array and the other ends quickly disappeared into the middle layer of the board. But, the one remaining identical device... was obviously in series with the LED. Okay, it's a resistor. The rest was easy with the other two now being easily found in series with usb d+ and d- leaving only the 470 ohm aref resistor as the missing device.