Issues encountered while recreating the PCB of the Teensy 4.1

[Shun]

We have created a new PCB based on the schematic diagrams published on the official website and assembled it using the original U2 chip and other identical components.


Issue 1:
After connecting to the computer, the board is not recognized by the Arduino IDE, and the red LED starts flashing.


Issue 2:
After pressing the RESET button, the red LED flashes twice, indicating an "NXP JTAG: No response" error. We also observed that VDD_SOC_IN has no 1.15Vdc output.


Issue 3:
When manually grounding the EN pin of the TLV75733P, the red LED flashes nine times, indicating an "ARM JTAG DAP initialization error
How can the above three issues be resolved?
thanks.

 

[defragster]

assembled it using the original U2 chip

Is this U2 being reused from a production PJRC Teensy - or a fresh DIY PJRC U2 chip?

Once a U1 and unused U2 power up together - they will only work in that combination IIRC PJRC has noted.

 

[Shun]

A fresh PJRC U2 chip

 

[PaulStoffregen]

When manually grounding the EN pin of the TLV75733P, the red LED flashes nine times

Your design must differ from the published schematic. In the Teensy schematic the red LED connects to U2 which is powered by the 3.3V regulator chip. If you short the EN pin to ground, the U2 output will lose power. Not only does it stop the output, but that regulator has a resistor that rapidly discharges the 3.3V power supply capacitors when EN is low. The red LED can't possibly blink under that scenario where U2 has no 3.3V powr.

I have no idea why it's not working. But from the limited info available so far, I'm certain your design is not really the same as the published schematic because you are seeing the red LED blink.

 

[Shun]

There was an error in how we described Issue 3.


The EN pin was pulled low temporarily and then released.
It was not held low.

 

[PaulStoffregen]

I don't know why your PCB isn't working.

Since you are seeing red LED blinking which requires 3.3V power, but you have no voltage on VDD_SOC_IN, seems likely something is going wrong with step 7 or 8 in the power up sequence. (see "Power Up Sequence" on the bootloader chip page)

If you can monitor the DCDC_PSWITCH signal, you could determine whether step 7 is working. This signal is default low. The bootloader chip drives it high to turn on the DCDC switcher. If you're getting logic high on that signal, then look at the connection of the inductor and capacitors.

2 quick blinks on the red LED is the expected response if the CPU can't power up. 2 blinks also is expected if the JTAG signals are connected between the 2 chips.

However, 9 blinks normally can only happen after a lot of other things are gone well. I don't understand how you're getting 9 blinks in some situations but only 2 blinks in others. That's very strange.

If you're only built one PCB, perhaps build another? We've had many custom PCB questions on this forum where the PCB design was ok and the problem turned out to be soldering or other construction problem.

If it still doesn't work, consider showing us the PCB layout and schematic. It's a long shot, but sometimes we have been able to spot mistakes just by looking at the design.

 

[Doug Forbes]

Why don't you just purchase a Teensy 4.1 from Paul. Save yourself all this trouble. In the end you could not have saved that much money doing it yourself. Just sayin'.

 

[PaulStoffregen]

I completely understand wanting to make a custom PCB. That's why we sell the bootloader chip. It's also why I've put so much effort into the documentation on that web page.

If your custom PCB isn't working, and you just can't find the problem, and you aren't willing to share the non-working design publicly so we might help see what's wrong, perhaps another way forward would be to make one of the designs other people have shared? On the bootloader chip page, scroll down to "User Shared Projects".

 

[theboot900]

Double check your schematic carefully against the official one and make sure your not missing any connections.

I head scratched 2 revisions with a 9 blinking error. Then I realised I hadn't connected 2 DCDC ground pins (n1 and n2)

The power up sequence worked. The bootloader chip would get locked to the cpu. Then the 9 blinks

 

[Shun]

Why don't you just purchase a Teensy 4.1 from Paul. Save yourself all this trouble. In the end you could not have saved that much money doing it yourself. Just sayin'.

https://forum.pjrc.com/index.php?threads/about-change-u1-on-the-teensy-4-1.76756/#post-356857
As stated in the issue referenced above, due to the need to mount new components on the PCB and the unavailability of bare PCB boards on the website, We are compelled to start with PCB fabrication due to the lack of other options.

I completely understand wanting to make a custom PCB. That's why we sell the bootloader chip. It's also why I've put so much effort into the documentation on that web page.

If your custom PCB isn't working, and you just can't find the problem, and you aren't willing to share the non-working design publicly so we might help see what's wrong, perhaps another way forward would be to make one of the designs other people have shared? On the bootloader chip page, scroll down to "User Shared Projects".

The hardware engineer is organizing the relevant design files and will upload them shortly.

Double check your schematic carefully against the official one and make sure your not missing any connections.

I head scratched 2 revisions with a 9 blinking error. Then I realised I hadn't connected 2 DCDC ground pins (n1 and n2)

The power up sequence worked. The bootloader chip would get locked to the cpu. Then the 9 blinks

As the meaning of the error indicator is unclear to us, we are uncertain where to begin the troubleshooting process.
We will conduct another round of checks.

thanks.

 

[Shun]

PCB 是根據該原理圖設計的。

 

[PaulStoffregen]

Can you share this schematic as a PDF? (now I see the PDF...) The image size is limited by the forum which make the text unreadable.

Can you also show the PCB layout? If something went wrong with power or ground connections, it may not be easily visible in the schematic but the layout will be easy to see if the pins that really need to connect to GND actually are wired.

 

[Shun]

Can you share this schematic as a PDF? The image size is limited by the forum which make the text unreadable.

The PDF has just been re-uploaded.

 

[PaulStoffregen]

Looking at the schematic, I see this questionable connection

Earlier I wrote "Since you are seeing red LED blinking which requires 3.3V power, but you have no voltage on VDD_SOC_IN, seems likely something is going wrong with step 7 or 8 in the power up sequence. (see "Power Up Sequence" on the bootloader chip page)"

If these 2 pins (DCDC_PSWITCH and GPIO_AD_B0_11) are connected to each other, but not actually wired to PTA3 on the bootloader chip, it would perfectly explain failure of the power up sequence step 7. The bootloader asserts PTA3 in step #7 to tell the IMXRT1062 chip to power up VCPU to 1.15V.

Recommend you look at this net on the PCB layout. Are all 3 pins really connected?

 

[Shun]

The attachment is the LAYOUT file.
Due to upload limitations, we are exporting the files layer by layer.

We’ve verified that DCDC_PSWITCH, GPIO_AD_B0_11, and PTA3 are electrically connected

 

[Shun]

The attached file includes the layout drawings for each PCB layer.