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LightningLogic

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Had a runaway print head heat. It just reads around 27 C so the head keeps heating! Left it alone to heat up and start a print. Bed heated correctly but the head never read correctly and got HOT! Warped/melted the red acrylic base. Fried the thermistor and even warped the print head! How do I get replacements and/or a fix? Thanks!
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Gary

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Reply with quote  #2 
Either the wiring, Arduino or Ultimaker board is messed up. If you don't figure out which it is, the new J-Head will burn up as well.

So, either the thermistor  was bad, the wiring in the 3D module is bad (including the connector), the wiring to the Ultimaker board is bad, or the least likely is that the analog port on the Arduino is bad.  If you get a new print module (which I assume will happen because yours melted), you will want to measure the thermistor resistance at the Ultimaker board in the controller box.

There are a lot of connectors in between the print head and the CPU. I'll bet that's where it failed.

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LightningLogic

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Reply with quote  #3 

Well, I ohmed the thyristor at the plugin to the Ultimaker and it's changing correctly. Checked the ultimaker for shorts or open in the RC circuit. That leaves the Arduino ADC on that pin being bad. I'm going to try the port swap firmware tomorrow night but my bet is on the Arduino port. Also, the temperature doesn't change much just stays around 27-30C. When I pull the head cable it still doesn't change.

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Gary

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Reply with quote  #4 
Bummer. Yep it's pretty much got to be the Arduino input.
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LightningLogic

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Reply with quote  #5 
Well, did a field change order and cut the trace to adc pin 8 and wired it to pin 12. Changed pins.h to match and she runs good. Now I just need ti change the print head and we're printing.
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Gary

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Reply with quote  #6 

I'm actually surprised that this isn't happening more, because of ESD.  The ADC is connected to the chassis. I sh*t you not.

http://boxzyunofficial.forumchatter.com/post/3d-print-module-connector-pinout-8077977?pid=1291962933

 

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LightningLogic

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Reply with quote  #7 

Yeah, I'm not a fan of hot chassis. The frame and any metal on it should be ground! I think I might just have to clean it up. I'm going to look into why the Ultimaker board is pwming negative.

 

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Gary

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Reply with quote  #8 

You can't put signal ground on chassis the way it's wired up now. It will short out the "thermistor" and make the Boxzy think the laser is installed.  I have been thinking of what the ramifications are to switching the "White Wire" line to the ADC input and then making chassis ground = signal ground...

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LightningLogic

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Reply with quote  #9 
I'm thinking three way switch and maybe a micro switch on the laser case for a safety. 
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Gary

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Reply with quote  #10 
Yes, a microswitch will work well with my mod. After working with lasers for, well, most of my life, I am very much more concerned about the beam being reflected off of shiny surfaces than of people firing the laser outside of its holder.  I'll be publishing a hack that isolates the frame and logic ground and keep the Analog0 input safe(er) - Probably Saturday when the parts come in.

Oh, by the way, the whole PWMing the negative is actually pretty standard when driving high-current loads with Open-Collector/Open-Drain driver circuits. It's a lot easier to drive low-side referenced transistors than high-side.  Hence things like the ULN2000 series relay drivers, etc.
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