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Hot end problems

Posted by cjensan 
Hot end problems
February 21, 2014 09:28PM
Hello all,

I'm a new user to the forum, but have had my printer since the end of Dec 2013.

It's a printrbot machine that a local fellow assembled setup and sold to me.

However I have had numerous difficulties (including a mainboard failure).

Most recently, I started to print with Taulman's 645. Excellent product btw!

I did roughly 12 hours of printing with this. Printing at a recorded 245C. right at the end of this print, the PEEK tube failed and the hot end was not being held.
I replaced the PEEK tube, taped it all back up, and went to print. I got 5 layers and the new PEEK tube melted.
So I checked and the thermistor was properly in the hot end. I let it cool, went back and brought it up to temp. I was about to start a print when I saw the temp on the screen shoot up to 270 ish and then give a temp failsafe protection. I turned off the machine, pulled out the thermistor, and looked. It had popped. I just got a new batch of 100k ohm thermistors. Plugged one in, and the temp remains at 251C even when it is at ambient temperature.

I have unplugged the thermistor entirely and it gives the same reading. The moment I power it up it reads 200C then jumps to 251C. I can plug the extruder temp into the bed temp and it reads exactly the same. So clearly there is either a software or hardware fault here.

Can anyone point me in the right direction?
Re: Hot end problems
February 22, 2014 12:11AM
I have managed to find the schematic here. [reprap.org]

With following this, I believe that I likely have a failed capacitor on the E-therm circuit as the reading is way off compared to the B-therm.

I will go to my electronics store tomorrow and get a couple 10uF surface mount capacitors, and replace them, and post an update..... I hate surface mount soldering btw.... thankfully I have solder wick and sucker.
Re: Hot end problems
February 22, 2014 03:12AM
Hi cjensan,

Welcome to the forum, this is the Reprap forum and specifically the Ormerod section, you may have more luck asking in a printrbot forum like [www.printrbottalk.com]


Limited Edition Red RS Ormerod 1 #144 of 200 - RRP 1.09fw
iamburnys Ormerod Upgrades Github
Follow me on ThingiVerse My Designs
Re: Hot end problems
February 22, 2014 01:22PM
Thanks Matt,

I had found a number of topics on this forum, hence asking again. Sorry about that
Re: Hot end problems
February 22, 2014 06:29PM
No worries, stick around, the more the merrier smiling smiley

Just thought you might get more relevant info from printrbot guys.


Limited Edition Red RS Ormerod 1 #144 of 200 - RRP 1.09fw
iamburnys Ormerod Upgrades Github
Follow me on ThingiVerse My Designs
Re: Hot end problems
February 22, 2014 06:36PM
I asked there but didn't get much more of a reponse.

Thought I should update here though.

The main chip (AT90USB1286) takes in the E-therm on pin 60. This is what has failed. It has caused an internal fault to ground with a resistance of .217ohm.
So in order to fix this, I have to replace this chip..... I can get replacement chips for around $25, but then I have to unsolder a chip with 64 pins that is smaller than the size of my thumb!!! I can do it. But what a PITA.

Anyone know if it is possible to change the code to accept the E-therm input from pin 59 or 58 of that chipset instead? From what I can see/read it is the same style input, and does not appear to currently be in use.....

I'm seriously thinking about replacing the thermistor with a J-type coupler and rewriting the code...... Then it just takes in a small mV and determines the temperature based off of that. Found lots of J-Type thermocouplers for around $14. They are much more sturdy than what is being used now. Think of it as a sensor that you really would never need to replace, or even keep a spare!
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