Yep, you heard me. Plugged in the supply, 5 seconds later heard a sizzling sound and a nice blue smoke came out from behind the display. Just before that, a couple of random columns went from black to yellow (the whole column, at once).
I haven’t had the pleasure to experience this acrid smell in quite a long time, so it brought back some memories. Unplugged the supply straight away and got ready to throw all out in case it caught fire, but it decided it was enough of a warning, and settled down slowly.
After I thought it was safe enough, I approached the beast to assess whatever damages I did to the poor thing. Luckily it seems it remained contained. One MIC2981 source driver is certainly out of service and was definitely the source of the smoke.
There might be some other damages but they are well hidden, as all other chips and PCB look fine to the naked eye. Nevertheless I was happy to have planned ahead and put the drivers on DIP sockets to facilitate replacement (as if I knew I would burn a few...).
What happened ? I’m not really sure, and it’s very annoying, as now I have this feeling it’ll burn again every time I plug in the supply. So far I think either one of the ground cable got disconnected and the ESP32 had a different ground reference than the control board, making its behaviour erratic, or the ESP32 had some power problem as it wouldn’t run the code properly when checking the outputs with the oscilloscope at a later stage.
The code itself wasn’t faulty as I wasn’t trying anything crazy or demanding as I have been in the previous log when blinking the whole display at max rate. The ESP32 wasn’t running the code for some reason, maybe was booting or re-boooting, during which the outputs went awol and may have loaded the shift registers with corrupted data, and at the same time sent a continuous pulse. This would explain the two columns flipping simultaneously, followed by the burning chip that couldn’t handle the current of that many simultaneous dots flipping (source and sink drivers are rated to 500mA per channel).
Legs up, as in... DEAD.
Having replaced the burnt chip, it seems I still have some troubleshooting to do as I cannot unflip dots. It’s a time consuming task and quite a setback as things were going so smoothly so far. I truly hope I haven’t damaged any of the coils or other parts of the display, but having been able to flip all remaining dots to yellow side seems reassuring.
I just finished soldering a second control board for my second display as I was about to try daisy chaining both displays, so I will probably use it to help isolate the remaining problems. Also, I may temporarily swap the ESP32 for an Arduino for more stability during the testing phase.
EDIT 26th August 2018 : The display is fine and doesn't have any damages. My control board has some burnt drivers, and 9 out of 12 shift registers have erratic behaviour. Those not being on DIP sockets, I'll have to re-solder a complete new board to go onto the next step of prototyping, ie. daisy-chaining, and making the LEDs work. It'll take a bit longer as I need to re-stock some components, but come back soon for updates !