Custom 3.6 Board, having trouble getting it operational

BrandonS

Member
Hello everyone, been having issues again getting a custom 3.6 board working. Had issues in the past that I was able to get through but now I'm having similar issues that are distinctly different. Old post for context

For context, this is a new iteration of an older board design that I previously had the "teensy 3.6" circuitry working. I was able to program the board and get it operational. This newer board has the exact same schematic with slight PCB routing differences, really shouldn't be causing any issues.

The two cases i'm seeing with this board, when I try resoldering either the bootloader or the crystals is

Case 1 The program pin floats at around 1.2V or so while the reset pin is high. If I pull the program pin low, the reset pin remains high. In this state, without pulling the program pin low, the 3.3V rail on the board is drawing around 24mA.

Case 2 The program pin and reset pins are high, If I ground the program pin, the reset pin gets pulled to ground, (from the previous post, Paul said this was a way to confirm that the bootloader chip is functioning), but then when I release the program pin from ground, it goes high, then very shortly after the reset pin goes back high. I'm guessing some process happens in that short period. Not an expert so not sure what is happening there.
In this case, the power draw on the 3.3V rail is about 18mA, distinctly lower than the other case.

Does anyone have an explanation to what may be going on in these two scenarios?
 
Update

Attempting to resolder the Bootloader chip is now resulting in one of two cases.

Case 1 Same as case 1 from before

Case 3 Similar to case 1 from above but now there was a case where the program pin stays low while the reset pin stays high. Grounding of the program pin, which it basically already is, has no effect on the reset pin.
Note: I checked and the program pin was not shorted to ground.
 
Alright, another update.

So it seems that case 1 and case 3 are essentially the same, the only difference is whether or not I have the USB cable connected. If the USB cable is not connected, the program pin floats as stated before, if the USB cable is plugged in, the program pin is pulled to ground. I'm essentially in a state that doesn't allow me to get the computer to recognize the board.

Does anyone know what it means when the reset line is high and the program pin is low, and the board is unresponsive to the computer.

I also successfully tested a barebones board that only has the essential Teensy components and was able to successfully communicate to that board as if it was a Teensy 3.6. So this design is proven, but the one fully assembled board just isn't working.
 
Bummer - no time to lose chips.

Some number have been produced before with PJRC bootloader and they worked?

Now altered layout and first one assembled not acting right?

Not a wide audience for help much, or much to go on.

Good news that partially completed shows as a T_3.6. Was the nature of the change wholly separate from the MCU and bootloader pairing? Other essential parts the same and connections in place?

Even part swaps with 'similar' items can affect results.

If the partial T_3.6 like board is completed ... does it work? If components are removed to that state from the completed board, does that work as a T_3.6?
 
Thanks for your reply.

So the board in question was the first board I assembled. Was never able to get it operational and the issues were as described.

Over the past couple days I assembled another board up to the same level as the first board. This one is working as expected so far. So the PCB design isn't the issue. I think the issue with the first board is either the MCU or the bootloader chip. I don't have any extra bootloader chips right now but I should have more coming tomorrow. I have however already tried two different bootloader chips on that board, so it may be that the MCU is the issue. Was just wondering if anyone out there had any similar experiences or knows what it means when the program pin stays low, or floats, and the reset pin stays high.

Given that the program pin is connected directly to the bootloader chip, I suspect that something funky is going on there that I don't currently have the knowledge to explain.

The changes from the older PCB designs to the new one don't change the MCU/bootloader circuitry or any of the other essential "Teensy 3.6" circuitry.
 
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