Bootloader blinks

Dogbone06

Dogbone06

Well-known member
Hey!

I just received a batch of custom boards with the PJRC bootloader. I've done this many many times.
But this batch, gives 4 blinks for some reason. I've tried swapping out the 24MHz crystal from a working board just in case. No luck.

I wanna try to swap the bootloader in case the factory (for some reason) used blank chips instead of using bootloaders from my stock (which I got from PJRC).
But the question is: Is the NXP fused now to the bootloader or is it not since we get the 4 blinks?

"4 Blinks = ARM JTAG & SWD Not Responding (Needs Crystal)The NXP JTAG communication is working, but communication with ARM JTAG or SWD fails. Usually this error means the 24 MHz crystal is not oscillating. NXP's JTAG does not require the oscillator, but the ARM JTAG does. This error also be caused by a bad connection between PTB5 to AD_B0_08, which is the signal that selects which JTAG controller is accessible."
ic_mkl02_t4_4blinks.png


EDIT: After trial and eror it turns out that it's something around the crytal. Not the crystal itself but some component. I am narrowing it down.
In other words, I got one board working by taking a few things from a working board.
 
Last edited:
defragster said:
Good work - Good Luck!
Click to expand...
I did some serious testing to get to the bottom of it. Turns out it truly was bad resistors on the whole batch. I got 10pcs of the Gen5 Dev boards. I figured I'd make a few since I only had one left.

All 10 boards the 2.2M resistor connected to the 24MHz crystal, where bad!
I have a book with resistors so once I located the issue I replaced the 2.2M with 1.8M and I also tried 3M. Both works fine.

I tried keeping the faulty 2.2M in place and just adding solder, maybe the solder they used are made from jungle juice or something. But that didn't work either.

Conclusing is, bad batch of resistors.
Funny thing is that I measured one of the bad ones and I got 2M, so within tolerance.

Very odd.
 
defragster said:
Wow - such extreme fail from such a single tiny part - and yet otherwise all else works ...
Click to expand...
Exactly. Those resistors that are on there, even tho they do measure correct resistance, must be baked or on crack or something. Truly odd.
Could probably dive deeper somehow but I don't know how. I've learned a good lesson at least. 4 blinks and I will always check that resistor first. And then other components around.

This has never happened before. And I've made over 1000 boards now during my years in this community.
 
I have the same problem but, thankfully, only on a couple boards, I'll try to check the 2M resistance and see if that does the trick
 
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