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Multiple Output Power Supplies
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Rapsey:
I have tried letting the printer idle for many hours and checking the serial connection debug logs for any errors or disconnects. So far it appears the issue does not happen when the machine is idle. So it might very well be EM interference from the steppers or a poorly shielded cable.

I didn't really want to burden you all with the details, seeing as it would take a lot of explaining before you could properly help me debug this thing. And also because I suspect it has to be really frustrating to troubleshoot something by remotely instructing a newbie. But you're right, you can't really give me advice without knowing the specifics so I'll give it a shot.

Let's start with the PSU. On the AC side we have: a yellow ground wire, a black wire labeled N and a red wire labeled L. These all go straight to the 220V mains and the red wire has the main power switch on it.

Now for the DC side. There is one V+/GND pair going into the main board and one pair going into a small MOSFET board. This MOSFET is used to control the bed heater, which is by far the biggest power consumer. It's something along the lines of 200W for the bed heater and 50W for everything else. The bed heater runs on 12VDC. It is PWM-controlled and uses the big-bang approach, meaning it alternates between fully on and fully off to maintain the desired temperature. But I should stress that I am experiencing this issue even when I'm not using the bed heater so I highly doubt this has anything to do with it.

Exiting this MOSFET board we have a black wire going to the bed, which leads me to conclude that the bed is PWM-controlled on the GND side. So presumably to turn off the bed heater it eliminates the voltage differential by raising the GND side to 12V, rather than lowering the positive side to GND. This would also explain why the third positive wire from the PSU goes straight to the bed heater.



Now for the main board itself. The V+/GND wires from the PSU go into the screw terminal on the left side of the board.



What's the red arrow you might ask? Well, one time after stopping mid-print I noticed this particular LED on the board was flashing rapidly. I have never seen this LED turn on before and I have no idea what it signals. This video shows it happening.

Unfortunately I have not been able to find a circuit diagram for this board. The closest thing I have been able to find was a diagram for an earlier version of this board. The layout has changed a little but it might still provide relevant insights so I'll include it here. The two attached PDF's show the wiring diagram and the schematics for this earlier version of the board.

I know that somewhere on this board there is some circuitry to convert the 12V to 5V. There was actually a problem with this because the manufacturer used a capacitor with insufficient capacitance, which resulted in an unstable 5V output. This was clearly visible because the voltage instability resulted in significant fluctuations in the temperature sensor readings which could be seen on the temperature graphs. After replacing the capacitor my sensor readings have been very stable to this day.

Lastly I do not believe that this problem is caused by some form of overheating. It doesn't seem to behave that way. Sometimes it will crash within 1 hour of starting a print, then when I restart the print immediately (without giving it time to cool down) it will run fine for 10+ hours. It would also be strange that it printed fine for hundreds of hours during summer, when it was 32C inside, but now in winter with 20C room temperature it starts acting up. I can't exclude overheating completely but nothing I have seen points in that direction.

Thank you all for your insights!
rstofer:

--- Quote from: Rapsey on February 25, 2019, 06:57:48 pm ---Exiting this MOSFET board we have a black wire going to the bed, which leads me to conclude that the bed is PWM-controlled on the GND side. So presumably to turn off the bed heater it eliminates the voltage differential by raising the GND side to 12V, rather than lowering the positive side to GND. This would also explain why the third positive wire from the PSU goes straight to the bed heater.

--- End quote ---
Low side switching is common.  We connect the load between V+ and the MOSFET drain with the MOSFET source connected to GND.  Then we PWM the gate.  No, the MOSFET doesn't pull up to 12V, it is either open circuit or pulling to GND.

--- Quote ---Now for the main board itself. The V+/GND wires from the PSU go into the screw terminal on the left side of the board.

--- End quote ---
The board input is labeled 12V-24V so you should be OK

--- Quote ---What's the red arrow you might ask? Well, one time after stopping mid-print I noticed this particular LED on the board was flashing rapidly. I have never seen this LED turn on before and I have no idea what it signals.

--- End quote ---
If you don't have the manual, you can request one from the web site.  I don't know that they will provide a schematic but they should describe the LED.  Let's just assume it is an error signal.

--- Quote ---I know that somewhere on this board there is some circuitry to convert the 12V to 5V. There was actually a problem with this because the manufacturer used a capacitor with insufficient capacitance, which resulted in an unstable 5V output. This was clearly visible because the voltage instability resulted in significant fluctuations in the temperature sensor readings which could be seen on the temperature graphs. After replacing the capacitor my sensor readings have been very stable to this day.

--- End quote ---
Well, the 12V is regulated to provide VREG-5V but that appears to go to a USB connection in the Interface section and comes back as VCC5V-M which is used all over the board.  There is also a VBUS connection.  It's not clear to me how this works because USB is 4 wires, not 3.  +5V, Gnd, D+ and D-.

I would take a look at what is happening here because it appears to be the source for all VCC5V-M.  Or maybe it's just another load and I didn't really find the regulator for the logic supply

--- Quote ---Lastly I do not believe that this problem is caused by some form of overheating. It doesn't seem to behave that way. Sometimes it will crash within 1 hour of starting a print, then when I restart the print immediately (without giving it time to cool down) it will run fine for 10+ hours. It would also be strange that it printed fine for hundreds of hours during summer, when it was 32C inside, but now in winter with 20C room temperature it starts acting up. I can't exclude overheating completely but nothing I have seen points in that direction.

Thank you all for your insights!

--- End quote ---
I had originally thought that the PSUs were a much higher voltage and regulators tend to get warm when the input voltage is much higher than the output voltage.

You might try to email the manufacturer and find out what the LED means.  It might flash in some kind of pattern to differentiate among several errors.
DinkyMods:
The one thing I still haven’t noticed you mention yet is have you flashed the firmware just ensure that there isn’t any corruption in the MCU.  It’s not uncommon to have random instability show up from Firmware issues.  It’s a simple thing to try before going to far down route of troubleshooting the hardware.   As the to stability of the 5V rail do you have a oscilloscope to be able to see any smaller variations since that can easily be tested at the MCU as it has a know pinout.
6PTsocket:

--- Quote from: Rapsey on February 24, 2019, 07:56:55 pm ---Great, thanks! I'll give it a go.


--- Quote from: CatalinaWOW on February 24, 2019, 07:10:57 pm ---Other possible problems would be noise or voltage regulation.  Your Turnigy supply is designed to charge batteries which don't really care about a few volts of ripple.  Not likely to be a problem.  If you have any kind of DVM you can at least roughly evaluate this.  Couple the supply to your meter through a capacitor and compare the AC voltage you see from both supplies.  If the Turnigy is not greatly larger than your original supply it is probably fine.

--- End quote ---
I suppose I can just use an oscilloscope to check the ripple. Why would you connect the meter through a capacitor? Wouldn't that smoothen out the ripple you're trying to detect?

--- End quote ---
The cap passes the AC component for you to measure with your DMM and blocks the DC component. If you measure a lot of AC (ripple) the charger may not be suitable, at least without some additional filtering.

Sent from my SM-G900V using Tapatalk

Rapsey:

--- Quote from: rstofer on February 25, 2019, 08:05:58 pm ---Low side switching is common.  We connect the load between V+ and the MOSFET drain with the MOSFET source connected to GND.  Then we PWM the gate.  No, the MOSFET doesn't pull up to 12V, it is either open circuit or pulling to GND.

--- End quote ---
Ah yes of course, that makes a lot more sense.


--- Quote from: rstofer on February 25, 2019, 08:05:58 pm ---Well, the 12V is regulated to provide VREG-5V but that appears to go to a USB connection in the Interface section and comes back as VCC5V-M which is used all over the board.  There is also a VBUS connection.  It's not clear to me how this works because USB is 4 wires, not 3.  +5V, Gnd, D+ and D-.

I would take a look at what is happening here because it appears to be the source for all VCC5V-M.  Or maybe it's just another load and I didn't really find the regulator for the logic supply

--- End quote ---
I think the USB connector is the 5 pins under "USB to UART" in the schematic, not the 3-pin USB thing in the "Interface" section. You can also see 5 wires going into the connector on the board photos. No idea what the 5th pin is. It could be part of the USB OTG standard or maybe it's just unused here.

The USB circuitry might be a bit weird because the 5V electronics on the board can be powered both from the internal 12V PSU and from the USB connection. So even with the PSU turned off you can interface with the printer via USB.

I should note that the problem also occurs when I'm printing from the internal SD card, without having anything connected to USB. So I doubt the USB circuitry is the culprit.


--- Quote from: rstofer on February 25, 2019, 08:05:58 pm ---I had originally thought that the PSUs were a much higher voltage and regulators tend to get warm when the input voltage is much higher than the output voltage.

You might try to email the manufacturer and find out what the LED means.  It might flash in some kind of pattern to differentiate among several errors.

--- End quote ---
I guess that would be the only way to find out. Will do, but it might take a while to get a reply from the Chinese manufacturer.


--- Quote from: DinkyMods on February 25, 2019, 08:45:47 pm ---The one thing I still haven’t noticed you mention yet is have you flashed the firmware just ensure that there isn’t any corruption in the MCU.  It’s not uncommon to have random instability show up from Firmware issues.  It’s a simple thing to try before going to far down route of troubleshooting the hardware.   As the to stability of the 5V rail do you have a oscilloscope to be able to see any smaller variations since that can easily be tested at the MCU as it has a know pinout.

--- End quote ---
When the problem started occurring I had already been using that firmware for several months without issues. But I did consider the possibility so I compiled a new firmware version and reflashed it a couple of days ago. Sadly no change, it still crashes like it did before.
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