No heat, but good fuses and power
Greetings
I have a month old i3 Mk 3 Prusa that will not heat. Printer had been in a student laboratory and working, but was found non-functional. I was asked to fix the machine.
Firmware 3.2.1-576
When the printer was brought to me, it did not function. On power up, the LCD displayed only black squares. I pressed the reset button and was able to regain control using the front panel.
I verified the power supply LCD, as well as 24 vdc to the mini rambo board input bottom left 4 screws, correct polarity.
I checked the two 5A and single 15A fuses on the rambo board, good continuity with multimeter, 0 Ohms.
When I selected preheat PLA, the front screen displays the following temperatures:
21/215
22/60
I powered off the machine and disconnected the A/C power cord. I disconnected the two thermistor connections at the rambo board and read their resistance at ~107 kOhms. I left them disconnected and attempted to preheat. The screen then read as follows:
0/215
0/60
I powered the machine off again and reconnected the thermistors. I carefully powered on the machine and placed it in preheat. Again, I was getting Room Temp / Setpoint for both. Using my multimeter, I checked the heatbed connection for voltage and saw none (millivolts). I also received no power from the extruder heater connection.
I powered the machine off again, and disconnected the extruder heater as well as the heatbed.
Extruder heater - 14.5 Ohms (from the screw terminals on the connector disconnected from the rambo board)
Heatbed - 2.7 Ohms (disconnected a single screw from the rambo board)
I was able to verify the machine has good stepper motor control, for X, Y, & Z. The machine will auto-home and seems to be properly calibrated along these axes.
Any assistance would be greatly appreciated.
Re: No heat, but good fuses and power
Your setpoint is 215/60.
The ambient temperature is 21~22C. You should let it heat a bit.
Re: No heat, but good fuses and power
Neither the bed nor the hot end are heating.
I flashed the firmware with the newest version I could find, 3.4.0-1327.
I have performed a factory reset - all data. During the first Self-Test checks, the two fans are verified working.
Next it attempts to check the hot end. A rotating "|" "-" appears next to hot end. During that time, no voltage is observed on the hot end connection at the EINSY MiniRAMBo oard. There is no LED light on the board next to the extruder heater connection. There is no voltage read with my handheld multimeter at the extruder heater connection.
Selftest error !
Please check :
Heater/Thermistor
Not connected
I disconnected the extruder heater and connected an external 12 V dc power supply. I was able to generate heat with the external power supply. During this time, I observed the display panel temperature reading for the thermistor change from 23c to 105c. I removed power from the heating element and returned it to the MiniRAMBo board. I again verified that 12 V dc was present at the 15A fuse, and verified the 15A fuse continuity when removed from the board. I also visually inspected the fuse, which appears to be in good functioning order.
Re: No heat, but good fuses and power
With those symptoms, I would suspect a problem with the power fail monitor (the thin black and white twisted cable from the power supply). If that wrongly sends out a power fail signal, the heaters are prevented from turning on.
Disconnect the cable from the Einsy, and then try preheating again.
Re: No heat, but good fuses and power
I was having the same problem. I disconnected the black and white wires, and the heating is working again. Now what? Leave them disconnected?
Re: No heat, but good fuses and power
Now what? Leave them disconnected?
If you can live without power fail recovery, then yes, you can just leave that plug unconnected.
You can also inspect the cable. Perhaps it has been pinched by a cable tie, resulting in a short. If not, the problem is with the power fail detector in the power supply, and then it is time to contact Prusa support for a replacement.
Re: No heat, but good fuses and power
I am going to look into that as soon as I finish this print. It's really strange that this would happen now. The printer has been sitting in the same location for over three months and this error suddenly comes up. I am using octopi, and I heard that power panic doesn't even work unless you are using a direct connection. I can't remember where I read that. Thank you for the response.
Re: No heat, but good fuses and power
I continued my troubleshooting with emails to Prusa customer support (W H).
I was asked if it could have been a bad board connection, and for pictures of the board, which I gave on 19 Sept
Up close pictures of the board, and with only the heaters, thermisters, and power supply connected.
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Prusa 21 Sept Response
Hello again,
Pardon my late reply. Do you have a multimeter around? I would like to see if the ports on the board is sending power, as well as checking the resistance of both heaters and their thermistors. Heatbed heater should read 3.8 Ohm, Hotend 14.4 Ohm and both thermistors should read 100k. Inspect the wires on the hotend as well, making sure it is not simply broken off. they are fragile.
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My 21 Sept Reply
Extruder heater - 14.5 Ohms
Heatbed - 2.7 Ohms
Thermisters - ~107K Ohms
Thermisters change value based on temperature. Applying heat with a heat gun causes the displayed temperature to change.
Applying external voltage to the extruder or heated bed causes them to heat up.
There is no voltage coming out of the board for either heat connection.
There is voltage on the 15a fuse, both sides, and the fuse continuity is good.
The board LEDs that usually come on when heating do not come on when trying to heat, neither in self test nor with manual settings.
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Prusa 21 Sept Response
Please, check all the fuses on the board, as well as on the PSU. Also, see what power is coming from the PSU.
Also, try to do a full factory reset, where you choose to clear all data. This clears old calibration and voltage data. Then flash to the newest firmware and calibrate again.
https://help.prusa3d.com/l/en/article/SYvbQ66IXF-factory-reset
If this is indeed a fault with the board we will replace it.
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My 21 Sept Reply
All of those asks have been previously addressed.
All voltages are proper. All fuses are good. All elements, EXCEPT the board, work properly with external voltages or multi meters connected.
My 24 Sept Reply
I have ordered a replacement board from ultimaker, installed it, and am printing again.
I am sure that the board itself has failed.
My 3 October Reply
Still no reply?
I have a dead board. I would like to get it replaced if possible. The fuses on the PSU, as well as the fuses on the board, were fine. It has been 12 days since I have heard back from anyone here.
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I have not yet heard back from Prusa. Printer has been retuned to service with an ultimaker purchased board for now, but if this is a warranty issue, I'd like to return this dead board and get an on hand spare for the university so that I can minimize downtime with any future issues.
Re: No heat, but good fuses and power
Just wanted to go back to this old thread and thank Prusa for resolving the issue for me. October 5th I was handled by a different support associate, and Oct 7th a new board was shipped towards us.
Mark as resolved, with thanks.