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Another dead board

Posted by DaGameFace 
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DaGameFace
Another dead board
February 21, 2016 03:28PM
So, I killed another 5v regulator on my new mega2560 board, only thing i did was adjust a potentiometer on a stepper motor while the power supply was turned on (not during a print or while preheating though).

Is this not something that's okay to do?

Regardless, I now have an atx power supply that is powering my printer and has unused 5V rails. Is it possible to bypass the mega's 5v regulator and use an atx 5v rail? (on a ramps 1.4)
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elwood127
Re: Another dead board
February 21, 2016 04:23PM
Not sure of the procedure on your board, but on my Melzi with power off, you have to switch a jumper from power supply to USB power before adjusting any pots.
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Dust
Re: Another dead board
February 21, 2016 04:44PM
Shorting the potentiometer will do that, as will shorting 5v to gnd anywhere (commonly threw endstops plugged in backwards)

1) never unplug or plug in anything electrical while it is on
2) always use non conducting screw drivers when adjusting pololu modules


Yes, if you remove D1 (to ensure you not sending any power to the damaged voltage regulator) Then you can feed 5v into any ramps board 5v line. Eg the 5v lines on a unused endstop plugs
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DaGameFace
Re: Another dead board
February 21, 2016 06:15PM
Thought my screwdriver was safe, its a rubber covered plastic handle. If i had known it was even a risk i would have turned it off, but i had no clue there was actually voltage going through the potentiometer.

Is D1 a specific pin? on the mega or ramps?

about to tear the printer apart, haven't yet
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JamesK
Re: Another dead board
February 21, 2016 06:21PM
Quote

Is it possible to bypass the mega's 5v regulator and use an atx 5v rail?

I tried that as it seems like the obvious thing to do, but at least with my PSU the 5V line is too noisy to use directly - it gave truly horrible results.
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Dust
Re: Another dead board
February 21, 2016 07:58PM
D1 is diode 1 on the ramps



Its under a stepper driver module
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DaGameFace
Re: Another dead board
February 22, 2016 12:50AM
horrible how?
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JamesK
Re: Another dead board
February 22, 2016 06:59AM
It looked like the noise on the 5V line messed up the ADC conversions, so the temperature readings were unstable.
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DaGameFace
Re: Another dead board
February 22, 2016 12:58PM
Can't I just put a 5v capacitor in line to stablize the current?
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DaGameFace
Re: Another dead board
February 22, 2016 12:58PM
Can't I just put a 5v capacitor in line to stablize the current?
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JamesK
Re: Another dead board
February 22, 2016 02:14PM
I was wondering if I could filter it (typically with a resistor or inductor and a pair of capacitors), but it was easier for me to just revert to alternative power. I'd be a bit worried about how much the 5V line drifts from the nominal voltage on my power supply - when the bed heater is drawing hard on the 12V the 5V line goes up to about 5.4V. I'm not sure what the upper limit of the mega2560 is, or the parts that draw on the 5V line like the LCD. Probably a better (if kind of complicated) solution is to use a boost converter to shift the 5V up to 7 or 8V, and then use a 7805 voltage regulator to produce a nice clean 5V for the mega.
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DaGameFace
Re: Another dead board
February 22, 2016 04:18PM
with no load my 5v rail is 5.10

under full printer load, (heated bed, nozzle and fans) the voltage drops to 5.03

I think this sounds promising enough to go ahead and try, plus i can add the capacitors to hopefully clean up the current. Unless someone thinks there could be a major problem here i am going to proceed.


Thank for all the responses
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JamesK
Re: Another dead board
February 22, 2016 08:25PM
That's good, definitely worth trying.
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Tocsin
Re: Another dead board
February 23, 2016 02:52PM
Now to put my other hat on, I'm a keen constructor of electronics, in particular in amateur radio. Noise from computer PSUs is a common problem in all kinds of areas. Most problems are due to relatively high frequencies and spikey pulses. You won't need big capacitors (in fact they will do nothing at all). Start off with something like 100nF across the 5V line, maybe paralleled with 100uFd at 25V rating.
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JamesK
Re: Another dead board
February 23, 2016 03:03PM
I didn't put the scope on it, but I suspect in my case the psu noise is fairly non-typical, and caused by the group regulation doing a very poor job of regulating the (mostly) unloaded 5V when the 12V is being cranked by the ~1 Ohm heat bed at 8 Hz. It's a pretty nasty setup for a power supply! It's interesting that DaGameFace (gotta love forum names!) reports much better regulation with his supply, so maybe newer psus have moved to independently regulated outputs.
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DaGameFace
Re: Another dead board
February 27, 2016 11:59AM
am using two 50v22uF capacitors that I had laying around with a 5v line from my PC ATX power supply going to one of the unused end stop positive leads. Everything working perfectly
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JamesK
Re: Another dead board
February 27, 2016 12:13PM
Nice! What's the make and model of the power supply?
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DaGameFace
Re: Another dead board
February 27, 2016 11:04PM
just a cheap insignia 400W that i got at best buy because my cheap china one died
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JamesK
Re: Another dead board
February 28, 2016 06:53AM
Thanks, I'll keep an eye out for one.
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