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Have I blown a component whilst testing my Ramps setup?

Posted by garyhodgson 
Have I blown a component whilst testing my Ramps setup?
March 06, 2011 03:50PM

I'm in the middle of building a Mendel Prusa and currently trying to test the electronics - with which i'm having mixed results. I suspect I may have blown some components whilst testing the end-stop micro switches, and would like some advice on whether what I did was completely wrong, or whether the problem could lay somewhere else. Any hints or pointers would be appreciated.

So, it's a Ramps v1.2 setup, and to test it I hooked in just one motor controller. The firmware loaded is johnnyr's Tonokip, and because I couldn't get Repsnapper to connect to the board (that's going to be another forum post I think) I am using the latest ReplicatorG binary.

With this setup I could get the motor to move via the ReplicatorG control panel, so I moved onto connecting a microswitch. Following a post I connected Common to Ground, Normally Closed to Signal, and put a 10k "pull-up" resistor across Signal and VCC (I didn't have a 4K7 to hand) (I may be showing my electronics ignorance here, please let me know if this is totally the wrong approach for hooking in micro-switches with Ramps) This setup actually worked as planned, initially. I could move the motor forward, and when in reverse the motor stopped when I pressed the switch. So far so good!

Unfortunately when I came back to the bench a little later, the motor had stopped reacting at all, even after removing the switch and going back to a "known good" point. After various combinations I tried with a second motor-controller, and this worked, but only in the positive direction. I also tried the original controller in a new socket and still couldn't get a response.

So I think I may have blown a controller, and potentially damaged the board, but i'm not sure, and am rather hesitant to proceed in case I do more damage. If anyone can point out glaring errors in what I have done, or suggest ways of testing if the board is ok (for example, where to prod it with a multimeter), I would really appreciate it.

Re: Have I blown a component whilst testing my Ramps setup?
March 06, 2011 07:19PM
First, never disconnect or particularly re-connect a motor from the RAMPS board while there is power to the RAMPS board. You will most likely blow the Pololu driver board for that axis.

Second, you may want to check how hot the Pololu for that axis is getting when the power is applied. When power is on, the motors are held still, which takes current to do. The Pololu's have a trimpot setting on them to adjust this current value. Set this to the middle of it's movement (best to use a multimeter and measure from the common wiper pin to one of the other sides while the power is OFF), and then tweak it for your setup. You need to make sure you can move the motors but 'only just'. I recommend using a multimeter because most people use the same motors on their setup, and the trimpots can sometimes turn indefinitely instead of stopping at the top and bottom of their range.

Third, you might want to resolder all the pin headers on the Pololu board. You may have a dodgy connection. Next I'd progress to the sockets on the RAMPS board, and then the pin headers on the RAMPS board that go to the Arduino MEGA.

Lastly, what is the current output of your power supply for the RAMPS board? If it's not very high, you may simply be drawing too much current for the supply. I have a 500mA power supply that had some 600mA LED banks on it (for lighting my work-desk). It worked fine for about 10-15 minutes, then started constantly tripping as the power supply internally overheated and started failing. I've seen the same issue with RAMPS and a not-quite enough current PSU. Works for a bit then fails.

PS: If the motor is not moving it could be that you are 'just' on the cusp of the necessary current setting, or that the current is set too high and the A4983 chip on the Pololu is overheating and shut down (it won't move if it's overheated to stop it being damaged).

PPS: Some of the firmware/host combos have been known to 'lock up' from time to time. Sometimes, you can just press the Arduino reset button (which is also on the RAMPS board) and it'll restart. Sometimes it doesn't work and you need to disconnect the power. If you've got the diode installed on the RAMPS board, you need to disconnect ALL power from the setup (which includes the Arduino USB cable), otherwise just unplugging power from the Arduino (eg: USB cable) will usually work.
Re: Have I blown a component whilst testing my Ramps setup?
March 07, 2011 02:30AM
Hi Cefiar, thanks for the detailed response - it really helps to be given pointers like this.

I suspect at some point I disconnected the motor from the RAMPS board without turning off the power, so it could be one controller lost in the name of learning. I'll test a new one and be more careful in future.

The Pololu's were set to a quarter turn, so I can try increasing that. The power supply is a standard ATX, so i'm guessing it should be ok, but will check that too.

My biggest hope of course is that it was a firmware/host lockup, as I turned of the 12v during reset in my testing, but didn't diconnect the USB - thanks again for the hint!

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