4.1 DOA or My Bad Soldering?

B

Beserker

Member
Hi, I have just soldered some header pins to a newly purchased Teensy 4.1, when plugged in to my pc via USB all that happens is the red LED next to the USB socket flashes 4 times at about 0.5 second intervals with a 2 second delay between flash cycles. The Teensy is not detected by my PC (windows 10) using 2 different USB cables both of which work with my 2 Teensy LC and my newly bought (no headers) 4.0. I stupidly didn't check to see if it worked before I soldered the headers. Is the flashing LED an error code, if so what does it mean as searching could not find me an answer.
Many Thanks.
 
There are details about the blinking on the web page: https://www.pjrc.com/store/ic_mkl02_t4.html

Code: 
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.

Don't know if it is DOA. But the first thing I would do is carefully look at all of your solder, to make sure you don't see any solder bridges. To either pin to pin or to some internal component.
Also check to see if it looks like something is missing. Sometimes if you are not careful, you could accidentally slip and knock off a component.
 
Blink codes are shown on this page: pjrc.com/store/ic_mkl02_t4.html

Not that it helps but:
Code: 
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.

When the RED Led is active the Teensy is offline under bootloader control, and factory blink doesn't connect to USB in any case.

Give the soldered board a close exam for any solder or rosin splash or shorts, if clear photos could be posted the forum can examine too.
Verify the surface components (top and bottom) are all properly in place against posted PJRC images.

Arrgh - bummer it wasn't powered and tested before soldering - takes effort to unpack and remember that step before proceeding - but PJRC did before packaging.

If there is some issue from soldering it won't help. After close examination noted above - the T_4.1 does have a 15 second Restore feature:
> with the T_4.1 powered press and hold the Button 15 seconds (LED should go off until the Flash) and release when the RED LED gives a FLASH.
> if the bootloader can talk to the MCU it will restore factory blink code to the T_4.1
 
Thank you both for your help with this issue. The problem has now been resolved. What I did to fix this issue was very carefully remover the black plastic from the headers to check the underside connections. I found pockets of solder flux under them. I washed the board under running water thinking that if I have killed it I may as well try everything. I left dryed the board off with compressed air to remove the majority of the water and then dry over night. When I checked the board in the morning, the red LED was now longer flashing and the Blink sketch was running and my PC was able to detect the board.
 
@Beserker - that is great news!

The Flux can be a problem for sure. Depending on the type 90% Isopropyl works to wash it off here - with an old toothbrush, then holding it in hand and hitting it with a hairdryer while I can just barely still hold it makes sure it all evaporates as I rotate it around making sure there are no trapped pockets. I usually wait as long as it takes me to walk upstairs to my computer (not long enough) - and plug it in to work. Not had issues after that washing process - not sure if it dissolves and rinses out of the black plastic - or maybe the solder used there has more flux that doesn't burn off the same.

@KurtE's crosspost beat mine because as usual I typed and walked away for something else and came back and hit post.
 
Fresh flux is a reasonably good insulator, the problem is as it ages it can oxidize, blacken and become conductive, and it can be very slightly conductive due to moisture (not usually a problem for digital circuits though, this is in the high megaohm ranges typically). I doubt flux will have caused the issue described unless you'd charred it to carbon by soldering for too long. You may have had a dry joint or a bridge (wicking of excess solder under the connector perhaps) and the disturbance you created investigating the joints by chance mechanically fixed the issue.

Reflowing the joints is the normal way to fix such problems, possibly removing excess solder first if the solder has formed convex blobs (good solder joints have surfaces of negative curvature).

Dry joints can be due to oxide build-up (clean PCB pads before soldering if not gold-plated), or issues like wrong iron temperature, not enough flux, not pre-tinning the bit. Using a flux-pen to pre-coat pads and pins with flux will help if the solder isn't wetting them readily.

It usually pays to buzz out newly soldered connections to make sure the electrons agree with your visual inspection(!).
 
You must log in or register to reply here.
Back
Top