Tracking down short circuits (RAMPS 1.3)

Well, I have assembled my RAMPS 1.3 [julianh72.blogspot.com] , and since I'm not exactly one of the world's greatest solderers, I'm taking the time to give it a thorough visual examination and continuity testing with a multi-meter before connecting it up to the motors and extruder, so that If I have shorted anything out, I will hopefully blow no more than one motor and / or one driver. My multimeter is telling me I have a short somewhere between my Ground and 5V lines.

It will probably take me a while to track down where the short is, as there are so many possible locations on the board where I may have dropped a blob of solder across the Gnd and 5V lines. I don't suppose anyone knows any good ways to track down faults of this kind?

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Follow my Mendel Prusa build here: [julianh72.blogspot.com]

Hi

[EDIT] Please ignore the following stupidity from me - I was confused and the following is complete rubbish.
Funnily enough I had exactly the same thing just last weekend. I had built a 1.3 and was doing continuity tests and had a "short" across 5v and Gnd. And for the life of me I couldn't remember if that was also the case with my previous 1.2 build. Anyway, turns out that the previous build also had this "short" but has been working consistently since the beginning of the year. So far the 1.3 build has been working fine too.

If someone could confirm that the "short" is supposed to be there, even though it doesn't seem to make sense in my complete-newbie-to-electronics eyes, I would appreciate it.

Cheers,
Gary

Edited 1 time(s). Last edit at 09/14/2011 04:58PM by garyhodgson.

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there should not be a short between 5V and ground. on my ramps 1.2 it is in the vicinity of 50kohms.

Gary,

Hmmm ... very strange! I will spend up to a couple of hours tonight trying to track down the possible short, but if I can't find anything, I might take a risk and try "firing 'er up", and hope I don't let any of the blue smoke escape from any of the little widgets on the board!

In hindsight - it might have been a good idea to run a continuity test on the PCB BEFORE I started soldering - but it's a bit late now!

I'll report back on what happens - one way or the other!

Edited 1 time(s). Last edit at 09/14/2011 12:53AM by julianh72.

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I was really cringing as I typed about my setup having this "short" because of course it doesn't make sense, I only wanted to share my experience so far.

I certainly don't want to cause anyone's electronics to blow up - so please make sure of everything before testing.

I'm going to review my setup tonight to get to the bottom of this.

Edited 1 time(s). Last edit at 09/14/2011 06:21AM by garyhodgson.

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Well, I can't for the life of me track down my short circuit - I am guessing it might be some excess solder that has flowed through to the top side of the board, hidden from view under a header or other component. Whatever it is, I can't get the correct voltage on the 5V line, and I can't see how the board can possibly work if it isn't giving 5V where it is required (not to mention the risk of overheating by running a dead short from 5V to ground).

Gary - when you say your board runs fine with an apparent short - have you tested with the board removed from the Arduino Mega, and all stepper drivers and jumpers removed, or were you doing your continuity testing with Stepper Drivers and Jumpers still in place? I don't know, but maybe these components might have low enough resistance to indicate an apparent short circuit when the board is powered down, but you might still get 5V when it is powered up? I can't see how the board would function without a source of 5V supply. When I strip my board right down (all Step-Sticks removed, and all jumpers removed), I still have a short from 5V to ground.

Looks like I may have no option but to strip the board down and start again!

(Guess I had better stick to my day job - which doesn't involve any soldering!)

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Well, I am a complete idiot! Whether from sleep deprivation, or just plain stupidity, I was completely confused about continuity I was getting across the 12v 5A pins (due to mixing the positive and negative pins) and confused this with your problem with 5V. I can only apologise for contributing to any confusion, and I sincerely hope I didn't cause any destroyed electronics by my erroneous statements - which I will edit and remove to stop anyone else from suffering from them.

Suffice to say when I retested my board across 5V there are no shorts - hence the board working.

Sorry, and good luck finding the source of the short.
Gary

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Aha! Thanks Gary - that makes more sense! I understand now, and I also understand the confusion that thinking while sleep deprived can bring.

(It was probably my own stupidity of enthusiastically soldering the board while suffering sleep deprivation that got me into this sorry mess in the first place! )

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OK, my rebuild is complete, and the good news is that I seem to have eliminated the short from Ground to 5V - yay!

However ...

I finished the soldering late last night (checking for local shorts / dry solders each time I soldered in a new component), and started doing some preliminary continuity / short circuit testing of the whole board. I don't have continuity between ALL the 5V pins on the board, when I test the RAMPS board in isolation (i.e. not piggy-backed onto Arduino Mega, no stepper drivers installed, no power hooked-up to board, but all jumpers installed on the 2x3 pins under each of the five stepper drivers sockets).

I figured I should put it away at that point and come back to it fresh tonight, but thought I would check here first:

Specifically, the 5V pad at the bottom left of the board (between the Reset Switch S1 and Diode D2) is continuous with the nearby 5V pads at bottom centre ("SERVOS" on the other side of the Reset Switch S1), but these pads are not electrically continuous with some of the more remote 5V pads (such as bottom right corner of the board - the top right pad on the 2x4 block called AUX-3 / SPI, and the nearby bottom pad on AUX-4). Is this expected, or should I be looking for some sort of short / dry joint on the 5V line before I piggy-back onto the Arduino Mega and apply live voltage? E.g. does the continuity of the 5V line depend on the presence of the Mega and / or the stepper drivers?

Thanks again for any advice! (Just trying to be very careful to test everything in isolation before I take the big step of applying live voltage and watching the pretty blue smoke waft away!)

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Never mind - I think I have it sorted out.

Having a close look at the conductor traces on the board (I have upgraded to a RAMPS 1.4 board, by the way; was using RAMPS 1.3 previously), I now see that the single pad labelled "5V" on the left side of the Reset Switch S1 and the 4 "5V" pads in the "SERVOS" set of pads to the right of Reset Switch S1 are all continuous with each other, but are not apparently connected to the rest of the "5V" pads on the board. All the rest of the "5V" pads are instead continuous with the "VCC" pad which is also just left of the Reset Switch "S1", and this in turn connects to the "5V" pin on the Arduino Mega (the third pin along from the bottom left corner).

As far as I can tell, I don't seem to have any shorts, open circuits or "cold joints", so I guess it is now time to wire it up to my machine, and hope for the the best!

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