Can't upload new program but old one still runs

[njanks]

I'm having a stranger error with my Teensy 4.1. Earlier today, I was testing some new code, and after uploading one of the changes I made, I was suddenly unable to upload any further code. The old program still runs fine, I can even see the serial monitor outputs. However, when I try to upload, I recieve an error that the "Teensy did not respond to a USB-based request to enter program mode". I have tried just about every combination of pressing the button. I have held it while powering on, I have pushed it while it is powered on, but neither have worked. How do I get back to uploading new programs?
It's also not the usb cable, as it's the same one I used earlier today to upload code. Any help would be great!

 

[Fluxanode]

Did you try rebooting the computer? I've seen this and a clean start-up helps me

 

[njanks]

I did try that. A fresh restart and update didn't seem to do anything :/

 

[njanks]

Just tried to upload to a second Teensy I have, which didn't work either - maybe it's something on my computer's end?

 

[Fluxanode]

Corrupted software?

 

[njanks]

I was able to get the second Teensy to work fine now. when I plug in the original, the red LED blinks twice. According to another forum post here (https://forum.pjrc.com/index.php?threads/teensy-4-0-red-light-is-blinking-and-not-working.72858/) it seems like the bootloader chip is having some issues if the two blinks is accurate. The weird part to me is that I had uploaded just fine earlier today! How would the chip have suddenly died for no reason?

 

[defragster]

With the LOADER online with the sketch ready to upload plug the Teensy in while holding down the Button, then release it?

If that fails perhaps try the 15 second Restore:
> get ready to count to 13-15 seconds and watch the RED USB end LED
> with powered Teensy press and hold the Button
> Watch for a FLASH of the RED LED and release the Button
> The RED LED should go BUSY for some time - watch for it to complete and go off while powered

That should reload a Factory Blink sketch and be ready for normal use

 

[PaulStoffregen]

2 blink error means communication problems between the bootloader chip and main processor. Usually this implies a hardware failure, like mechanical stress on the PCB caused either chip to sever from its pads. We've also seen cases where soldering leaves flux or other conductive residue which interferes, though the most common of those is problems with the crystal, which gives 4 blink error.

 

[njanks]

Thanks for the advice. I've moved on to attempting to reflow the bootloader to see if a solder joint over there failed. However, now I'm stuggling to get it off! My heat gun and a bunch of tacky flux seem to have done nothing.

 

[njanks]

Update again: looks like it just took a lot more patience than I originally had! I ended up reflowing the bootloader chip, but the double blink issue still occurs. Maybe the break is somewhere else?