Heater Turns on Automatically

Im running a gen6 board with marlin v0.9.10b on it, and as soon as i power up the board the heater starts going . it has a steady 10.3V going to it and only thing ive changed firmware wise is inverting a few motors and setting board type to gen6 and commenting out the heated bed line. i have the resistor wired to pins 3&4 .

also in pronterface if i have heat set to off the led next to heater on the board is off , if i set it to on then the led does turn on. but the heater is always on even if its set to off in pronterface.

The same thing also happened in the old firmware my gen6 had on it , which im thinking was the stock gen6 firmware, dunno its been a while.

EDIT___
just tried with the latest sprinter firmware , and it still does this

would that mean its a problem with the board ?

Edited 2 time(s). Last edit at 01/28/2012 10:59PM by Rooski.

Is it on while you press RESET button? If so, it may mean either a shortcircuit or a broken MOSFET.

For some reason the software think I am spamming ... I do not know how to clean this message though.

Edited 1 time(s). Last edit at 01/29/2012 10:32AM by misan.

Yeah it still gets 10v when i hold the reset button , and the thermistor get 5v . When i was first installing the thermistor i did accidentally touch the 2 leads together and it sparked and the psu turned off , but nothing seemed to have fried, and nothing looks burnt. how would i check for sure that the mosfet is broken ? also the thermistor works fine , gives back good reading (fluctuates alot though).

Edited 1 time(s). Last edit at 01/29/2012 02:01PM by Rooski.

If there was a short in the heater it is almost sure your mosfet is dead. Shorting thermistor would cause no harm though.

Im sure I didn't short the heater , it has the thick resistor wires and they are far apart and I have everything soldered well. There have been a few people with the same problem and it is either their wiring or firmware issue. But if it is the MOSFET can I get a link to some info on how to replace it, I really don't have the cash for a new board : /

I have no experience with Gen6, maybe other folks can help. I guess it is T1 what you have to replace. [www.reprap.org]

It should be one or two bucks only (it costs around $0.20 in quantity).

Shorting the thermistor leads would not cause a spark because it is only connected to 5V via a 4K7 resistor that will limit the current to 1mA. Did you perhaps have the thermistor and heater leads swapped?

If it is on with the reset button pressed that rules out firmware because it hasn't run yet.

A spark will destroy an unprotected MOSFET.

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[www.hydraraptor.blogspot.com]

Perhaps I had the wires switched since I Kindof rigged a 6pin molex , I now have them soldered to the pins for testing , I guess I'll replace the MOSFET and post results.

Since i have no experience reading circuit diagrams , can someone tell me where the mosfet is so i dont mess the board up even more , and what kind of mosfet (link/partnumber). Thanks for the help guys.

EDIT__
Im guessing this is the mosfet chip ?



Edited 4 time(s). Last edit at 01/30/2012 01:39AM by Rooski.

I have found out that is the MOSFET chip, but im not sure what one to replace it with , I'd like a protected one so this won't happen again, any suggestions?

Some boards (ie RAMPS) do have a short-circuit protection built-in fuse but Gen6 does not. Whether this might have avoid you this problem or not, I do not know. But you may put one of them in series with your power supply like the big yellow one in this picture: [reprap.org]

Still, I think you need to replace the MOSFET by a similar one. It is uncommon for this to happen again (exercise caution against shorts though).

i searched for the text on the chip , but nothing came up. it says

(weird Sybol/character) p011h
x6f0_ 
f874

on the face of the chip.

Edited 2 time(s). Last edit at 01/30/2012 05:20PM by Rooski.

It's IRF8714PBF (SO-8 package). It is written in the schematic of Gen6 in the wiki or in the BOM.

[parts.digikey.com]

[www.mouser.com]

Digikey does not have it in individual quantities. Edit: Mouser is out of stock...just noticed.

[www.newark.com] Newark has it.

I would recommend cutting the leads from the bad chip and cleaning the pads...it is difficult if you have very little soldering experience to remove IC's without risk of damaging the board. You will need a decent soldering iron with a fine pitch tip.


Where are you located? There may be a reprapper nearby that has SMD soldering capability that can help if you don't have the proper tools. I know I can help if you are in my area.

Edited 2 time(s). Last edit at 01/30/2012 09:57PM by C. Cecil.

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Message if there is anything you need...I have more than what is listed on my site.
Located in the Spokane, WA / Coeur d'Alene, ID area.
Contact: Robosprout@gmail.com Flickr: [www.flickr.com]

Im in north east PA near Wilkes-Barre/Scranton , i have a fine tipped iron , and am fairly sure id be able to get it on. i do have a friend that is an electronics engineer and he solders all the time, but im not sure if ill be able to meet up with him anytime soon. so if anyone is in the area and willing to help out it would be much appreciated.