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Hotend heats up on power on until MAXTEMP  

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barney15e
(@barney15e)
Active Member
Hotend heats up on power on until MAXTEMP

When I power on the Mini, the hotend begins to heat up until it reaches max temp. 

Measured the heater (good) and tried the thermistor, but my meter doesn't have a wide enough range. I can see the needle move a bit, but I don't have the resolution to verify exact Ohms. The bed thermistor matches the movement of the hotend thermistor, so I'm not sure it is a thermistor problem. 

The day started with a bad first layer print. After stoping and restarting the print, the Y-Axis stopped moving. The motor did not move smoothly at all. I disassembled and tested the Y-Axis on the X-Axis port. It started working again. After reconnecting all the wires to their correct locations, I powered it up and move each axis successfully. I then started the Wizard. Before the Wizard could complete, I got a MAXTEMP error. 

Could this all be something in the buddy board?

Best Answer by JoanTabb:

@barney15e

My Mistake, it's a mini not a mk3. 

if the heater is heating whilst the printer is Idle, 
I suspect Q3 is short circuit or the control circuit is faulty. 
regards Joan

Posted : 02/06/2021 4:09 am
cwbullet
(@cwbullet)
Illustrious Member
RE: Hotend heats up on power on until MAXTEMP

Make sure the Thermistors are fully plugged in and into the right slots.  I suggest that you contact support via chat on the main shop page.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 02/06/2021 9:32 am
Zoltan
(@zoltan)
Moderator
RE: Hotend heats up on power on until MAXTEMP

@barney15e

would be great you send the display picture when the heating starts after the start to see what temperatures are displayed and what colors, 

if it is a real heating controlled by FW or a HW fault casued by heater power transistors shortcut .

FW version to know would be also a benefit.

Would b also great to provide more detailed information like here described : We want to help you, you have to tell us ... – General discussion, announcements and releases – Prusa3D Forum (prusaprinters.org)

This post was modified 2 months ago by Zoltan
even an old man can learn new things 🙂
Standard I3 mk3s, FW 3.10.1 RC1, no closed box, sketchup , fusion 360, PrusaSlicer, Windows 10
PRUSA MINI FW 4.3.2-rc2 technical background, Prusa Connect Beta...
Posted : 02/06/2021 9:41 am
Zoltan
(@zoltan)
Moderator
RE: Hotend heats up on power on until MAXTEMP

Maxtemp could identify a shortcut thermistor or real reach of the maxtemp threshold. What does whow your hotend temperature?

even an old man can learn new things 🙂
Standard I3 mk3s, FW 3.10.1 RC1, no closed box, sketchup , fusion 360, PrusaSlicer, Windows 10
PRUSA MINI FW 4.3.2-rc2 technical background, Prusa Connect Beta...
Posted : 02/06/2021 9:48 am
barney15e
(@barney15e)
Active Member
Topic starter answered:
RE: Hotend heats up on power on until MAXTEMP

@zoltan

FW: 4.3.1 (4.3.0, when problem started).

Hotend heats up. Temp display shows it heating up, also. Commanded temp is 0°.

How do I upload a video? Do I have to have it hosted somewhere and link to it?

 

This post was modified 2 months ago by barney15e
Posted : 02/06/2021 12:20 pm
cwbullet
(@cwbullet)
Illustrious Member
RE: Hotend heats up on power on until MAXTEMP

If your temp is reading zero, you most likely have a bad thermistor wire, connector, or controller boatd.  Have yopu contacted support via chat?  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 02/06/2021 12:27 pm
barney15e
(@barney15e)
Active Member
Topic starter answered:
RE: Hotend heats up on power on until MAXTEMP
Posted by: @cwbullet

If your temp is reading zero, you most likely have a bad thermistor wire, connector, or controller boatd.  Have yopu contacted support via chat?  

I contacted Chat about the Y-Axis, but the chat appears to be closed, now. At least, I don't get an option to contact them.

The hotend will heat up without the thermistor attached. It starts heating as soon as power is applied and doesn't stop for anything except disconnecting the heater or powering off.

Posted : 02/06/2021 12:36 pm
barney15e
(@barney15e)
Active Member
Topic starter answered:
RE: Hotend heats up on power on until MAXTEMP
Posted by: @cwbullet

If your temp is reading zero, you most likely have a bad thermistor wire, connector, or controller boatd.  Have yopu contacted support via chat?  

Well, the thermistor is reporting the correct temperature, so it appears to be working correctly. There is something telling the hotend to heat up, and the fans respond accordingly as it heats up. So, it appear the thermistor is sending info back to the controller.

From the time it powers on, there is 24V on the Hotend pins on the board.

This post was modified 2 months ago by barney15e
Posted : 02/06/2021 12:55 pm
JoanTabb
(@joantabb)
Moderator
RE: Hotend heats up on power on until MAXTEMP

@barney15e

if the commanded temperature is 0C and your heater is heating, I would suspect the einsy board

do you have a multimeter? 

If you do, and you are feeling confident, turn the printer off, unplug the heater cable, that goes to the extruder, then measure the resistance between the heater pins and ground they should not be short circuit.

Test point 17 is on the underside of the board... 

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 02/06/2021 1:03 pm
barney15e
(@barney15e)
Active Member
Topic starter answered:
RE: Hotend heats up on power on until MAXTEMP
Posted by: @joantabb

Test point 17 is on the underside of the board... 

regards Joan

Are you suggesting I measure between the pins and TP17?

I measured between the pins and pin to any of the shielded metal parts on the board. Got about 1.3k between those. The pin farthest from the bed heater connection goes to ground, directly. Looks like it should be about 100k. Bad board? 

I'll take the board out later today and see if there is anything underneath shorting it out. Got to go to work, now.

Thanks

Posted : 02/06/2021 1:35 pm
Zoltan
(@zoltan)
Moderator
RE: Hotend heats up on power on until MAXTEMP

@barney15e

what I read when you get the maxtemp red scree the nozzle does not start cooling.

 If it stays hot, switch off the printer till the board replacement not to get more damages.

The symptoms lead me to conclusion - the power transistors or the procesor output pin are shortcut - HW fault 

Seems it is not FW dependent as it started in previous release.

Contact support for buddyboard replacement.

even an old man can learn new things 🙂
Standard I3 mk3s, FW 3.10.1 RC1, no closed box, sketchup , fusion 360, PrusaSlicer, Windows 10
PRUSA MINI FW 4.3.2-rc2 technical background, Prusa Connect Beta...
Posted : 02/06/2021 2:41 pm
JoanTabb
(@joantabb)
Moderator
RE: Hotend heats up on power on until MAXTEMP

@barney15e

My Mistake, it's a mini not a mk3. 

if the heater is heating whilst the printer is Idle, 
I suspect Q3 is short circuit or the control circuit is faulty. 
regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 02/06/2021 3:24 pm
barney15e
(@barney15e)
Active Member
Topic starter answered:
RE: Hotend heats up on power on until MAXTEMP

@joantabb

With the buddy board completely disconnected, I measure about 9 ohms and 12 ohms on each of the heater pins. Get the same for the bed pins.

I get zero ohms between pin 3 of the MOSFET and the ground.

 

Posted : 02/06/2021 10:55 pm
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