| Electronics > Beginners |
| Pulling my hair out. Circuit boards stop working once shipped to client and more |
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| mcinque:
--- Quote from: OwO on June 01, 2019, 05:07:42 pm ---First thing you really have to do before considering anything else is to triage the failures and get to the bottom of it --- End quote --- --- Quote ---Action items right now: debug the boards that do fail testing, try to find the exact root cause, record all observations. --- End quote --- Exactly. Investigation on dead boards is essential. There are too many causes and considerations to find the problem without proper debugging. Absolutely analyze where those boards failed and report your discoverings, possibly together with a schematic. |
| Psi:
--- Quote from: Jackster on June 01, 2019, 03:54:04 pm ---I have the boards that have failed from when clients used them. More than half worked as expected. Some did fail testing. QC is done by hand. I run the boards on a test program for 24 hours. We also test after this that the PWM input, switches and firmware all work. ... The boards are encased in an aluminium block with >1.5mm wall around with a few cutouts for buttons and display. --- End quote --- Do you by any chance put screws into this aluminum case? If so are they pre-threaded? Thread forming screws (or just tight screws) into aluminium creates lots of metal filings! The metal flakes may not cause a problem initially but after being shaken around in transport maybe they get all over the place and short IC pins. Test: Put down a clean sheet of copy paper on a desk. Grab a finished unit and carefully open it up on the paper. Tap out the board & case and see if any metal flakes come out. The paper will give a good contrast to make them easy to see. --- Quote from: Jackster on June 01, 2019, 03:54:04 pm ---This product gets used all over, but most boards that have failed, arrived to the user bad. My hunch was xray but I have nothing to back that up with. --- End quote --- Normal airport x-ray is totally fine, that wont do anything. Only the high power X-ray's used to sterilize mail are a concern. Those are usually found at government buildings. --- Quote from: Jackster on June 01, 2019, 03:54:04 pm ---I use an Arduino to load the boot loader onto the ATMEGA and then a FTDI for flashing firmware. AVRdude checks and we make sure it confirms all is good. Not sure about the ATMega328p doing this or not. --- End quote --- FYI - There's a new chip out, the ATMega328PB which is not the same as a ATMega328P. It's easy to think 'oh that's just the lead version' but no, it's a different chip with some different pinouts. --- Quote from: Jackster on June 01, 2019, 03:54:04 pm ---I do use those programming pins for the NRF24L01. --- End quote --- Right, so the ATMega328 SPI pins is used for flash programming of the MCU and also for talking to the NRF24L01 chip over SPI? How are you handling the reset line on the ATMega328? Is it pulled high externally? Is it connected to an external button or something? I just wonder if it's possible for the ATmega to go into reset state for some reason while comms to NRF24L01 are active and somehow get garbage send to the ATmega while it's in reset low state (program mode). I'm not sure this is actually possible, because there should be no SPI clock once MCU goes into reset. I'm just thinking out loud. Maybe someone else will have a through reading this. |
| Psi:
Have a look at these 2 areas on dead PCBs. There maybe issues where the track has broken or shorted etc.. |
| Psi:
How are you handling merging of the USB Vbus power onto the 5V from the voltage regulator output? Normally you would diode OR the two sources, but from the pcb layout it looks more like connecting 5V usb to reg output? Voltage regulators do not like a higher voltage on their output than their input. They tend to die. That can happen if you connect 5V from USB onto the output of a 5V reg and then remote the battery that's powering the input! I could see you doing all QC test with a battery always connected but a user connecting USB first because they have a shinny new toy and can't wait to plug it in before they can source a battery. |
| Jackster:
--- Quote from: Psi on June 02, 2019, 12:56:44 am --- --- Quote from: Jackster on June 01, 2019, 03:54:04 pm ---I have the boards that have failed from when clients used them. More than half worked as expected. Some did fail testing. QC is done by hand. I run the boards on a test program for 24 hours. We also test after this that the PWM input, switches and firmware all work. ... The boards are encased in an aluminium block with >1.5mm wall around with a few cutouts for buttons and display. --- End quote --- Do you by any chance put screws into this aluminum case? If so are they pre-threaded? Thread forming screws (or just tight screws) into aluminium creates lots of metal filings! The metal flakes may not cause a problem initially but after being shaken around in transport maybe they get all over the place and short IC pins. Test: Put down a clean sheet of copy paper on a desk. Grab a finished unit and carefully open it up on the paper. Tap out the board & case and see if any metal flakes come out. The paper will give a good contrast to make them easy to see. --- Quote from: Jackster on June 01, 2019, 03:54:04 pm ---This product gets used all over, but most boards that have failed, arrived to the user bad. My hunch was xray but I have nothing to back that up with. --- End quote --- Normal airport x-ray is totally fine, that wont do anything. Only the high power X-ray's used to sterilize mail are a concern. Those are usually found at government buildings. --- Quote from: Jackster on June 01, 2019, 03:54:04 pm ---I use an Arduino to load the boot loader onto the ATMEGA and then a FTDI for flashing firmware. AVRdude checks and we make sure it confirms all is good. Not sure about the ATMega328p doing this or not. --- End quote --- FYI - There's a new chip out, the ATMega328PB which is not the same as a ATMega328P. It's easy to think 'oh that's just the lead version' but no, it's a different chip with some different pinouts. --- Quote from: Jackster on June 01, 2019, 03:54:04 pm ---I do use those programming pins for the NRF24L01. --- End quote --- Right, so the ATMega328 SPI pins is used for flash programming of the MCU and also for talking to the NRF24L01 chip over SPI? How are you handling the reset line on the ATMega328? Is it pulled high externally? Is it connected to an external button or something? I just wonder if it's possible for the ATmega to go into reset state for some reason while comms to NRF24L01 are active and somehow get garbage send to the ATmega while it's in reset low state (program mode). I'm not sure this is actually possible, because there should be no SPI clock once MCU goes into reset. I'm just thinking out loud. Maybe someone else will have a through reading this. --- End quote --- I have the screw holes pre-threaded on the cnc. The whole case is then cleaned, bead blasted then anodised. They are super clean. I am aware of the ATMega328PB. I make sure not to order or use them. I burn the bootloader before installing the WiFi board. But burning while it is on, not had any problems with that either. The reset pin on the ATMega328p is shared between ICSP header and the FTDI chip. There is a 0.1uF cap to ground. This is all to Arduino spec I believe. --- Quote from: Psi on June 02, 2019, 01:23:00 am ---How are you handling merging of the USB Vbus power onto the 5V from the voltage regulator output? Normally you would diode OR the two sources, but from the pcb layout it looks more like connecting 5V usb to reg output? Voltage regulators do not like a higher voltage on their output than their input. They tend to die. That can happen if you connect 5V from USB onto the output of a 5V reg and then remote the battery that's powering the input! I could see you doing all QC test with a battery always connected but a user connecting USB first because they have a shinny new toy and can't wait to plug it in before they can source a battery. --- End quote --- So the power is always delivered via the 16v input. The only time users use USB is to test the device and update firmware. Both are not used at the same time and we make that very clear in the documentation. The power is as per Arduino spec for the Arduino Nano. --- Quote from: Psi on June 02, 2019, 01:20:06 am ---Have a look at these 2 areas on dead PCBs. There maybe issues where the track has broken or shorted etc.. --- End quote --- Ill check, thanks for spotting. |
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