Magic smoke when connecting to power

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Magic smoke when connecting to power

Postby ChrisCartwright » 2017-Jan-Mon-22-Jan

I connected my PSU to the control board and turned it on. Almost immediately, I heard a pop and smelt smoke. Looking at the board, U1 and U2 both gave up the magic smoke. The rest of the board looks fine.

I tested the voltage on the PSU and got ~12.3 volts while powered on. The printer had been running fine for the last 18 months on the same PSU. I was doing some work on the table that printer sits on, and tipped it on it's side multiple times to connect/disconnect power. I don't see any loose wires or anything else that might cause a short circuit.

I have taken apart the heated bed upgrade and added heat shrink tubing to the wire on the bed and temperature sensor. I was careful to keep the temperature sensor itself exposed so its readings should not be affected.

I have ordered a new G series board that should be arriving sometime this week.

Assuming a short was the issue, my current plan of attack is to put the new board in the printer and hook it up to a constant current source. If the current source shows the board using more than ~100mA, then I know there is still a short somewhere in the system. The constant current source should stop the new board from giving up the magic smoke. If there is a short, I'm not sure where to start looking or what to test and how to test it.

I ordered a 'DROK® LM2596 DC Buck Volt Regulator' as my constant current source. I can set it to 12v and limit current to 2A, which would be well below the maximum for the board.

I have attached some pictures of the fried components. Picture of U1 isn't great, my camera didn't seem to want to focus on it. I'd like to start using the printer again, any help in diagnosing the issue would be appreciated.

Thanks

Chris
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Attachments
IMG_20170114_191007051.jpg
U1-ish
IMG_20170114_190805612.jpg
U2
ChrisCartwright
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Magic smoke when connecting to power

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Re: Magic smoke when connecting to power

Postby RetireeJay » 2017-Jan-Tue-07-Jan

U1 is the 5V regulator that steps down from 12V to 5V on the board. I haven't looked up its specs, but normally voltage regulators protect themselves against short circuits (to ground) on their outputs. So I'm thinking that something shorted 12V into the 5V rail; that would explain why U2, which is a motor controller chip, also smoked. This would make all the other motor controller chips at extremely high risk for being fried, even if they didn't visibly burn up. Replacing the board is a good idea. I'm not so sure about the Rev G; I think you'll find it very different and with very different firmware requirements. Good luck.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
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Re: Magic smoke when connecting to power

Postby ChrisCartwright » 2017-Jan-Sun-19-Jan

I'm hoping the revision G isn't too different from revision F seeing as the new Simple uses it. On the whole, I just need it to work well with OctoPrint.

Do you have any suggestions on how I could find the short? A current limiter wouldn't protect against a short between the two rails. I've cleaned up the connections on the heated bed. I don't think the steppers would short the rails, but I'm doing some research on how to check them anyway. I also want to make sure they weren't damaged.

Chris
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Re: Magic smoke when connecting to power

Postby ChrisCartwright » 2017-Feb-Fri-22-Feb

For those that may be interested:

Finally have my printer up and running again. Turns out, the molex extension that printrbot sells has an ambiguous head pattern. I had attached it to the CPU cable instead of the PCIe cable. It fits on both and is a better match to the CPU cable, so assumed that was the correct one.

Always double check the documentation.

Chris
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