Fried my extruder board, advice please?

A month ago I fried the motor driver on my first techzone extruder V2.2 board because I missed a step in the instructions to adjust the pot down, it came cranked all the way up. I plugged it in with the motor hooked up and the chip blew immediately. After it fried, as soon as 12V is connected the motor driver glows and smokes... I couldn't even use it to continue testing anything, so i bought a new board.

The second board arrived, and after reading up on my instructions about the motor portion, i turned the pot down, triple checked my connections and got the motor to work forwards and backwards without problem. hurray! I installed all 4 motors on the frame, tensioned belts, and re-tested. All 4 motors move (in only 1 direction for XYZ but they do work, i was planning on tackling that problem later). I continued in the instruction blog for testing the thermocouple and heater. The thermocouple was reading 20-22, i put my hand on it for a bit and it increased a degree or two. Things were moving along well.

Then I hit the 'turn heater on' button and the chip 738N6L chip immediately smoked. Now when I power the extruder board with 12v I can still control the motor, but I have to leave the heater element disconnected. The thermocouple ohms out at 10.1 ohms and still gives accurate temperature reading. The LED indicator next to C+/C- is always on now. The C+/C- screw leads read a short, and when I check the resistance of the heater element in the extruder tip, it also reads 0.5 ohms. What is a typical ohm out of the heater supposed to be? I should have checked it before I hooked it up, and now i feel stupid.

I have a bad feeling that not only do I have to buy a 3rd extruder board, but I think that I will also have to build a whole new extruder tip. I'm getting very discouraged. I'm looking for suggestions, i'm finding the instructions to build my reprap impossibly hard to follow. They mostly seem half complete, out of order, with poor picture quality, and it's very confusing. (my apologies for ranting, it's been a good / bad day on the project).

[www.flickr.com] -my board

[reprap.org] -electronics page i follow
[reprap.org] -my extruder tip

... use your first extruder with the burned driver and a separate pololu-driver for the extruder motor - the two-H-bridges-driver on the extruder is suboptimal

You can wire the CLOCK/DIR-wires from the motherboard directly to the extra motor driver (with a proper GND-connection) and use all the other functions from the extruder.

The 'only one direction'-problem of your stepper drivers is most common solved with activating the endstops - without them the software tries to 'leave the homing switch' and won't drive in the other direction ...

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

The extruder heater should be about 6 ohms. If it reads 0.5, then its likely shorted.

You can still use the second board, you just have to change the pin definitions in the extruder firmware so you can use a different mosfet to power the hot end.

If you open your extruder firmware and look in the configuration.h file (down near the bottom) you will see this

// MOSFET drivers

#define BED_OUTPUT 15
#define FAN_OUTPUT 11
#define HEATER_OUTPUT 12

Change it to this (if you don't have a heated bed)

#define BED_OUTPUT 12
#define FAN_OUTPUT 11
#define HEATER_OUTPUT 15

Upload it to the extruder board and then you can use A+/A- to power the hot end...... once you get the hot end fixed

Thanks for all the help. I ordered a pololu driver, a new hot end kit. When they arrive, I will make the software changes to the second board. I was thinking that the first board would probably work still if I removed the burned up h-bridge... but i'll try that if the second board software fix doesn't fly. Thanks again.

@jeffwilson, if your skilled with a decent fine tip soldering iron, you can cut the leads off the chip and use flux and desoldering braid to remove the old legs then buy a new chip (~5$) and just carefully setup the new chip, its not too hard, i was actually able to build my first set of gen3 electronics with only a decent soldering station and lots of time, might be worth the time instead of buying a new board, you can also do this with the blown mofset easily. but it turns out, if you can use an external stepper controller, it will run much nicer, quieter and cooler. and just simply swap the mofset pins to use a different one. just make sure you quadruple check the resistance of the stuff you plug in, the heater should be around 6-8 ohms, if you want assistance repairing your old board, pm me, we can see what we can work out. good luck

jeffwilson Wrote:
-------------------------------------------------------
...
> reading. The LED indicator next to C+/C- is
> always on now. The C+/C- screw leads read a
> short, and when I check the resistance of the
> heater element in the extruder tip, it also reads
> 0.5 ohms. What is a typical ohm out of the heater
> supposed to be? I should have checked it before I
...

You definitely have a short in your extruder heater element or leads. If you touch the leads of your meter together, you'll probably see 0.5 ohms also.

I won't give up on the extruder controller yet. The LED is on to indicate that the mosfet is active in order to supply voltage to your heater. After all, your temperature reading is below the set temperature. Does it go off if you turn the heater off in the software? If so, it might still be working.

The + side is always connected to +12V and the - side is shorted to ground by the mosfet to complete the circuit. To test it, you should measure the voltage between the + and - terminal, not the resistance. You can also measure the resistance between the - side and ground and it should be very low (less than 1 ohm) when the LED is on and open when it's not.

Unfortunately, mosfets tend to fail short circuit so I think it's fried

---

-----------------------------------------------
Wooden Mendel
Teacup Firmware