Hi everyone! I’ve been working on a microcontroller-based project that was rock solid on a breadboard,, but I’ve hit a bit of a mystery after moving the design to a custom PCB. While the jumper-wire prototype felt very stable, the PCB version is behaving unpredictably—specifically during startup... It’s not completely broken, but the boot up isn't always clean; sometimes peripherals fail to respond until I mamually hit the reset button or cycle the power.

I’m trying to step back and look at the bigger picture instead of just cChasing one signal. For those with more experience, what are the first assumptions you usually challenge in this situation? I’m starting to look into power rail stability during the initial ramp-up, MCU reset timing, and whether my GPIO pins are in an undefined state at boot. I’d love to hear about your mental checklist for transitioning from prototype to PCB... are there common layout 'gotchas' or power-up habits that helped you catch these issues early in your later revisions? I've been checking resources like the EEVblog decoupling guide and standard MCU startup docs, but personal insights from the community would be invaluable. Thanks for sharing your experience!

 

You can start by telling us the part number of the MCU and posting the circuit schematics.

 

Welcome to AAC

As already said, schematics and, in addition, PCB layouts (individual layers, not composite please) will help us advise you.

 

You need to post what your doing probably brown out the chip voltage drops cause it no longer has the capacitance the bread had

 

That’s a solid point, MrChips. I should have specified earlier. this design is based on an STM32H7, which I know can be quite particular about power-up sequencing and noise on the VCAP pins....

I’ll prepare a clean PDF of the schematic and high-res exports of the individual PCB layout layers (specifically the power/ground planes and the MCU fanout).... I'll make sure to highlight the reset circuitry, the bypass network, and the LDO/regulator section. Having more eyes on the physical implenentation should definitely help spot any startup corner cases or decoupling oversights I might have missed. Thanks for the guidance!

 

Welcome to AAC

As already said, schematics and,,, in addition, PCB layouts (individual layers, not composite please) will help us advise you.

Thanks for the welcome, Irving!

That makes total sense. I’m preparing those files now... I’ll make sure to upload the schematic in a searchable PDF format and provide clear, individual exports of the PCB layers (Top, Bottom, and internal Power/Ground planes) rather than a composite view.

I’ll also include a close-up of the STM32H7 breakout area and the power entry stage, as I suspect the startup glitches might be tied to how I’ve routed the decoupling for the VCAP and VDD rails. I should have everything posted in a few monents. Thanks for being willing to take a look.

 

You need to post what your doing probably brown out the chip voltage drops cause it no longer has the capacitance the bread had

That makes sense. I actually used the ST AN5419 (Hardware development guide for STM32H7) as my primary reference when starting the layout, specifically following the recommendations for the VCAP and VDDA filtering. However, looking at it now, I might have focused too much on the 'ideal' values in the app note and didn't account for the loss of bulk capacitance that the breadboard was providing. I'll re-examine the power section against the reference to see where the PCB version is falling short.
https://www.st.com/resource/en/appl...7-hardware-development-stmicroelectronics.pdf
https://github.com/pms67/H7-Video-Processing-Board