MotorDynamicsLab
Short Circuit on the 3.3V Line / 5V Line
Hi, So I think (although I'm not entirely sure) that I might have overheated the board I've got In other words I'm accepting it as my own fault, but I'm just posting the details for info here The end result is a
- A direct short on the 3.3V line to ground
- Around a 78 ohm short on the 5V line to ground
- 24V line I think is fine
Currently I'm testing with a current controlled power supply to see if I can locate the short.
For context, I'm using a LDO Voron Kit 350mm revision D, using the Leviathan board. To give some background it was a hot day at the time (around 28C) and I was printing ASA material with a 90C bed. The fans in the base are located to blow across the board. But The wiring wasn't fully tucked away and the bottom skirt not fully printed to guide the air so I'm accepting it as my own fault, there's also a filament dryer located next to it as well.
On an attempt at a reset of the board the following neopixel IC popped the magic smoke, although it wasn't wired to anything, so I'm wondering if there was a surge on the 5V rail which triggered it (or maybe the rail got really hot, but ether way there was a sizzling sound)
So far I've removed that IC but that wasn't the cause, more of a symptom I think. I've got some PCB freeze spray on order to see if I can locate where the short is, although I've already ordered a new board at this point. Moving forwards I might stick a heatsink on the STM32, make sure all the cables are tucked away and be a bit more careful with the cooling, such as relocating the filament dryer so it's not right next to it.
Hi, So I think (although I'm not entirely sure) that I might have overheated the board I've got In other words I'm accepting it as my own fault, but I'm just posting the details for info here The end result is a
- A direct short on the 3.3V line to ground
- Around a 78 ohm short on the 5V line to ground
- 24V line I think is fine
Currently I'm testing with a current controlled power supply to see if I can locate the short.
For context, I'm using a LDO Voron Kit 350mm revision D, using the Leviathan board. To give some background it was a hot day at the time (around 28C) and I was printing ASA material with a 90C bed. The fans in the base are located to blow across the board. But The wiring wasn't fully tucked away and the bottom skirt not fully printed to guide the air so I'm accepting it as my own fault, there's also a filament dryer located next to it as well.
On an attempt at a reset of the board the following neopixel IC popped the magic smoke, although it wasn't wired to anything, so I'm wondering if there was a surge on the 5V rail which triggered it (or maybe the rail got really hot, but ether way there was a sizzling sound)
So far I've removed that IC but that wasn't the cause, more of a symptom I think. I've got some PCB freeze spray on order to see if I can locate where the short is, although I've already ordered a new board at this point. Moving forwards I might stick a heatsink on the STM32, make sure all the cables are tucked away and be a bit more careful with the cooling, such as relocating the filament dryer so it's not right next to it.
I can hardly imagine that you have overheated the board. U15 is also far away from any heat sources (DCDC converters as an example) I have already tested the board without active cooling at much higher ambient temperatures in my Trident. In this test, the MCU had a temperature of just over 80°C.
Still a bit of a mystery at the moment, I just tried some cold spray on the pcb to see if I could identify the short without much success so I'll be getting a thermal camera in a few weeks to see what the results are.
To recap it was in the middle of printing some ASA material, then I noticed it had stopped. The Rpi was still running and it showed a USB connection to the head as well. But the usb connection to the main board had dropped out and the backlight leds had turned off.
Next I tried turning the power off and on, that's what then triggered U15 to sizzle and give out a puff of smoke, best guess is the 5V regulator tried to ramp up the voltage briefly to compensate for the large current draw due to some sort of short, or the copper trace overheated perhaps, so more of a symptom.
Still a bit of a mystery at the moment, I just tried some cold spray on the pcb to see if I could identify the short without much success so I'll be getting a thermal camera in a few weeks to see what the results are.
To recap it was in the middle of printing some ASA material, then I noticed it had stopped. The Rpi was still running and it showed a USB connection to the head as well. But the usb connection to the main board had dropped out and the backlight leds had turned off.
Next I tried turning the power off and on, that's what then triggered U15 to sizzle and give out a puff of smoke, best guess is the 5V regulator tried to ramp up the voltage briefly to compensate for the large current draw due to some sort of short, or the copper trace overheated perhaps, so more of a symptom.
Do you use 5V fans in your printer?
Still a bit of a mystery at the moment, I just tried some cold spray on the pcb to see if I could identify the short without much success so I'll be getting a thermal camera in a few weeks to see what the results are. To recap it was in the middle of printing some ASA material, then I noticed it had stopped. The Rpi was still running and it showed a USB connection to the head as well. But the usb connection to the main board had dropped out and the backlight leds had turned off. Next I tried turning the power off and on, that's what then triggered U15 to sizzle and give out a puff of smoke, best guess is the 5V regulator tried to ramp up the voltage briefly to compensate for the large current draw due to some sort of short, or the copper trace overheated perhaps, so more of a symptom.
Do you use 5V fans in your printer?
24V ones, the same ones that come in the LDO Rev D kit One correction though, I'm seeing a 1.6 ohm resistance across the 3.3V line and 78 ohm resistance across the 5V line, it's not a complete short on 3.3V
Still a bit of a mystery at the moment, I just tried some cold spray on the pcb to see if I could identify the short without much success so I'll be getting a thermal camera in a few weeks to see what the results are. To recap it was in the middle of printing some ASA material, then I noticed it had stopped. The Rpi was still running and it showed a USB connection to the head as well. But the usb connection to the main board had dropped out and the backlight leds had turned off. Next I tried turning the power off and on, that's what then triggered U15 to sizzle and give out a puff of smoke, best guess is the 5V regulator tried to ramp up the voltage briefly to compensate for the large current draw due to some sort of short, or the copper trace overheated perhaps, so more of a symptom.
Do you use 5V fans in your printer?
24V ones, the same ones that come in the LDO Rev D kit One correction though, I'm seeing a 1.6 ohm resistance across the 3.3V line and 78 ohm resistance across the 5V line, it's not a complete short on 3.3V
Then I assume that the 5V LED lights up but the 3.3V LED does not. The 3.3V regulator will therefore switch off.
24V ones, the same ones that come in the LDO Rev D kit One correction though, I'm seeing a 1.6 ohm resistance across the 3.3V line and 78 ohm resistance across the 5V line, it's not a complete short on 3.3V
Then I assume that the 5V LED lights up but the 3.3V LED does not. The 3.3V regulator will therefore switch off.
I've just done a bit more probing
- between the output and ground for PS2 (12V regulator) - 2 Ohms resistance
- between the output and ground for PS3 (5V regulator) - 2 Ohms resistance
- between the the 3.3V line and ground for U11 (3.3V regulator) - 2 ohms resistance
before I was measuring on one of the connectors for the 5V line, but this time I measured directly across the regulator output Typically the resistance should be around 2K or more across each of those lines (tends to go up as the meter is charging the caps on the rail) looking at the working board I've got Pretty strange
Just an update, I managed to find the fault The cause is a short across the input / output pins (1 and 3) of PS3 the 5V regulator. It also had a low resistance down to ground. This meant that a higher than normal voltage (24V) ended up on the 5V line
This then caused U15 to explode because it takes 5V in normally Also this damaged the 3.3V regulator I think because this feeds from the 5V line the end result is a resistance of around 1.8 ohms across the 3.3V line which shouldn't be there (after removal of the 5V regulator)
12V regulator seems fine Rpi I think is fine, that's fed from a different 5V regulator PS1 and that's still outputting 5V correctly
With 3.3V applies directly I'm seeing heat on the main MCU and the 3.3V regulator but the heat on the MCU isn't that much so it might just be the regulator that is blown will compare against a working board to see if it's just the regulator thats blown