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Short circuit or too big current?

Posted by jedynywiking 
Short circuit or too big current?
December 10, 2012 07:01AM
Dear Gen7 users,

after scratching some spare time, finally I managed to wire my Prusa Mendel, and solder the Gen7 board.
Unfortunately, it burned... In particular, I supposes there is a short circuit somewhere, since one of the paths on the PCB got destroyed.
I attach the scheme with marked part that went vapour.
Now, here are some detailed specifications of my case:
- Gen7-1.4.1 board provided by Traumflug;
- Gen7-1.3.1 Opto Endstops;
- standard PC power supply;
I pluged in:
-- power winking smiley
-- hot end;
-- hot end's termistor;
-- 3 Opto endstops
No motors were connected.

To forestall some suggestions:
- I checked the voltage levels on the board before installing the chips, all acceptable;
- I checked the voltages after installing the chip;
- I checked the endsopts, all connections, resistances etc seem OK (no short circuits there);
To be completely fair, I have to mention, that during the first time I plugged the power to a chip-less board, I fried 100uH Coil (part L1). It got replaced, and of course I triple- checked the board eliminating what seemed to be the problem. As mentioned, the voltages were OK on all the board.

I was running the first "test" form section "Your First Firmware Upload" of the Gen7. manual.

The first try, with no Optos, only power plugged in, worked fine.
The second try: I got a bit overconfident, I plugged all three Optos, hot-end and termistor. I fried the path.

I am not an electronics expert, but it seems to me that either there is a problem on one of the Optos, or the circuit path simply did not withstand the current.

I want to replace the damaged path with a piece of wire. Still, I would be very grateful for any suggestions on what to do or check not to burn my house down.

Waiting for your kind replays!
open | download - 778px-Gen7_Board_1.4.1_Layout.png (301.8 KB)
Re: Short circuit or too big current?
December 10, 2012 01:04PM
Opto Endstops shouldn't draw more than 20 mA, more likely like 5 or 10 mA. By far not enough to burn a copper track. So obviously, one of the opto endstops produces the short.

Plugging power into a chip-less board shouldn't burn the coil either. Looks like you have a short elsewhere or a defective C19. You can remove C19 for testing, it's just a noise canceling capacitor.

To find shorts, hold the electronics against a light source. Light goes through copper-less areas much better than through copper or solder, so shadows show harmful solder blobs.

Generation 7 Electronics Teacup Firmware RepRap DIY
Re: Short circuit or too big current?
December 10, 2012 01:43PM
Thank you for your very fast answer! It helps a lot.

Regarding the burned L1, I checked the board for shors after frying it, but will have to do it again with the light trick (so obvious, never popped into my head). The same will do with the optos.

Thanks again!
Re: Short circuit or too big current?
December 11, 2012 05:17AM
To fix a solder blob, a solder sucking pump is really helpful. Suck away what's there, then solder again. Soldering twice doesn't harm at all, so do it as often as you want. Just make sure you never overheat the copper or it'll disconnect from the board. A bit of patience is a good helper, too.

Generation 7 Electronics Teacup Firmware RepRap DIY
Re: Short circuit or too big current?
December 15, 2012 07:02PM
Fixed the problem.
There was a short on the endstops.
The printer works and moves.
Thank you!
Re: Short circuit or too big current?
October 09, 2013 04:59PM
I thought there was a short circuit in your Gen7 board due to which the large current was flowing through your board and that damaged the tracks of the board so the best thing you could do is just check the continuity of the circuit with the help of multi-meter.

PCB cost
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