Strange PCU & RAMPS Behavior
September 10, 2014 05:15PM
Couldn't seem to find anyone else with this problem, so if anyone could help me it'd be much appreciated.

I've never built a Reprap before and I've been sort of piecing one together through buying things from ebay and other sources. At the moment I have the Arduino Mega, the Ramps 1.4, the smart lcd, and the stepper motors, as well as an old HP ATX power supply that gives 12v 16A.
I had it all plugged in and working just Saturday night, everything working well. When I got the motors in, I decided to try and wire them up and test them. When I wired them up all they did was vibrate, didnt move. At some point the LCD ended up showing a bunch of random code and moving the dial just scrolled through it. I shut it off, and started it back up and it all worked fine again. I tried the motor a second time with different wiring and it did the same thing. I'm not sure if I left the ramps on after the code showed up this time, but I noticed the Arduino was very warm by the power input, and I think the screen had just white boxes on it.
Now, whenever I plug the RAMPS in with the power supply it doesn't want to work. The 11A input simply shows the white boxes on the LCD, and the 5A input doesn't seem to do anything (though I guess I dont know whether it's SUPPOSED to do anything with power is going solely to the 5A input. I tried using a lower output rail from the power supply and the LCD lit up but didn't show anything. Is some kind of amperage limiter blown to where its getting too much current? Is one of the fuses broken? I'm at a loss and don't really know what I'm doing!
Re: Strange PCU & RAMPS Behavior
September 10, 2014 10:15PM
A 16 amp power supply, especially an old one, is marginal for a reprap. I would think that as the current draw approaches the limit of the power supply that problems would start to show up. You should have a bit of a buffer in there. My printers are both powered by 30 amp power supplies, but I wouldn't go below 20. Also, the 11 amp power connection powers the heated bed only. I don't know why it would cause anything to show up on the LCD.
Re: Strange PCU & RAMPS Behavior
September 11, 2014 12:53AM
You can test your Arduino and LCD by just plugging in the USB power to the board. If everything is ok it'll power up and display the main screen information on the LCD. If the screen is light without display try adjusting the LCD trimpot on the back, which adjusts the contrast. It sounds to me like you had something wired wrong (like the endstops) and blew the D1 diode. You can test this also by supplying power via the USB port, If the LCD works when you do this but not when just on 12 power it means at least the D1 diode is bad and need to be replaced, although you could have more damage beyond just this. Another source for garbled screen information is interference with the unshielded LCD cables...
Re: Strange PCU & RAMPS Behavior
September 11, 2014 01:11AM
Well I'm a newbie as well but I have worked on some crazy HW in the past and it sounds like a HW issue.
First disconnect the 11A during the test.
I would advice to use a DVM fist check the ramps for the 12[v] than all the other voltages (5[v] )it should produce.
If that is OK than you need to test the Arduino - same check voltages it's easier.
Report back & it will be easier to eliminate problems (I never had this issue so I don't have good suggestions)

About your motors I had the same thing & one of the wires of the motor wasn't connected to the ramps board while in another motor the connector was OK but the wire was broken in the middle.
When you have a wire problem and SOME of the wires are OK but some aren't the PWM that should arrive the motor doesn't arrive.
In this stage the motor starts to act but stops while outside we see the motor vibrating.
So: check all your motors in all the connections if 1 motor is OK than all the rest should be connectivity issues.

Edited 1 time(s). Last edit at 09/11/2014 03:52AM by polkary.
Re: Strange PCU & RAMPS Behavior
September 11, 2014 12:44PM
Here's the problem though: I didn't have anything else plugged in. It was just the power supply into ramps/arduino, the LCD attached, and the motor connected. There should've been nowhere near 16 amps pulled from the power supply. Is it possible that an incorrectly wired motor could damage something? Also, how do I test the diodes and fuses to make sure they're working properly?
Re: Strange PCU & RAMPS Behavior
September 11, 2014 01:46PM
I Have read somewhere that PC PSU's do need to detect some load on the 5V rails else they won't output correctly

see this taken from

Greg's I3 Kits

Granted this is for a UK PSU but the technique should be the same and is certainly worth a try!

- Power supply for standard RepRap 3D printers. These are high power, Alpine brand 12V 34A 600W ATX supplies that deliver more than enough power to run a heated bed and a couple of extruders. We've been using them on our Prusas without any problem. Note that this is requires 230V AC Input, if you live outside of the UK/Europe - e.g. North America - this power supply will not be suitable.

To balance the load on the 12V lines, power resistors need to be placed on the 5V and 3.3V lines. These are included, along with heatshrink tubing (may be different to that pictured). See the second picture of our separate power supply listing for how to do the wiring to power the RAMPS board:

cut off all connectors, then wire:

4 black, 2 yellow to 5A; 8 black, 4 yellow to 11A (black to negative, yellow to positive)

1 orange 1 brown & 1 green 1 black to 4R7 power resistor

1 red & 1 black to 10R power resistor

group by colour and insulate all other unused wires with heat-shrink tubing (this is included, along with solder for the wiring of the power resistors)

Note that the power resistors get very hot during normal operation - to avoid burning yourself, do not touch them when the power is on. We’ve found that cable tying them to the back of the power supply - the side with the power switch - helps with cooling as they get air flow from the fan.

Included is a power lead with UK plug for UK orders, and a European Schuko plug for International orders.

Note: due to current supply constraints on ATX power supplies, the power rating may be slightly different (550W, 650W or 700W instead of 600W) on the unit you receive, but it will be effectively functionally the same with regards to powering the printer.


Re: Strange PCU & RAMPS Behavior
September 11, 2014 06:31PM
Heres some additional info that I didnt mention. When plugging it in by USB (by which it works perfectly) an LED on the arduino flashes and goes off, while the ON LED stays on as usual. However, when I plug the PSU in, the other LEDs all light up and stay lit, and my computer loses connection with the arduino. Also, when the PSU is plugged in and the LCD is all white, if you look at an angle, or just after I disconnect power, you can see what SHOULD be showing on the screen. It's almost as if the contrast is turned all the way up. If I leave it plugged in for a while I hear pops and it starts to smell and get hot, so I know I have to have destroyed something right? It might be coming from the voltage regulator or the overcurrent protection. I'm lost and I dont know what I'd need to replace or how to tell.

At the moment I'm thinking that somehow, when I plugged the motor in and attempted to move it through the interface on the LCD, it somehow overdrew current and damaged something on the board. I don't know why this would happen as a stepper motor shouldn't pull an extreme amount of current, especially without anything else connected to draw more current. I'm not sure if something failed or if something shorted or what. Any Ideas?

Edited 1 time(s). Last edit at 09/11/2014 06:43PM by stutzman.
Re: Strange PCU & RAMPS Behavior
September 11, 2014 09:12PM
My guess is you have blown one of the diodes, check D2, or just remove it. Also it could be installed backwards. It is used for running in non USB mode( sd card). But it should get you running again. The diode is a 1N4004, if you need to replace.
Re: Strange PCU & RAMPS Behavior
September 11, 2014 10:50PM
What are the differences between D1 and D2 and their purposes? And would the popping noise be the diode or something beyond, and would it now be blown too?
Re: Strange PCU & RAMPS Behavior
September 11, 2014 11:16PM
Here is the info on the RAMPS1.4 []
It will do a better job of describing their purpose.
These diode allow power to flow only one way, so that you don't over power the Adruino board.. d2 anyway.
Popping noise? That is a bit of a mystery not sure what would make that moise, but be assured it is not good.
Re: Strange PCU & RAMPS Behavior
September 12, 2014 01:49AM
All of what you described are symptoms for shortage.
You need to first find source of issue verify that the arduino is OK than move to ramps (why? it is easier):
a. Disconnect your ramps from the arduino.
b.Connect to arduino using usb only and burn the example BLINK project on it.
c. If that doesn't work than you have at least damaged the arduino if it works continue to d..
d. Burn the firmware & connect only the LCD if that works your issue is probably the ramps only
if that doesn't work your arduino my be damaged less severely than in previous stage
Now if all is OK than ramps is to blame... so do as other members (I have nothing better to offer smiling smiley

1 rule: "starts to smell and get hot" => that means something is burning disconnect power at once.

Edited 1 time(s). Last edit at 09/12/2014 02:11AM by polkary.
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