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I was working on my printer when something metallic came into contact with the pcb. I smelled smoke and quickly unplugged the printer. Anyway, this is the result and, of course, the heat bed won't heat.

Can this be salvaged or should I toss it and buy a new one?

shorted

update the heat bed was not hot at the time. I had the heat bed unscrewed from the chassis but had forgotten to unplug the printer. I am not exactly sure how it shorted but I think it shorted between the power lead connection and the thermistor.

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  • $\begingroup$ FYI I have already ordered a new one for $20 but I still want to see if I can fix this one for the experience. $\endgroup$
    – zkent
    Apr 21, 2016 at 14:58
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    $\begingroup$ Worth noting here that all heaters in a 3D printer are always energized with positive voltage. The ground side is what is switched. So shorting any heater element to ground will cause current to flow, whether or not it's "on." $\endgroup$
    – Ryan Carlyle
    Apr 21, 2016 at 15:23
  • $\begingroup$ @RyanCarlyle what is the difference as it's in fact a resistor? According to my knowledge it doesn't matter if you change polarity (checked on Mk2 HB - as same as in the case). The only difference is that LED is lit or not. $\endgroup$
    – darth pixel
    Apr 21, 2016 at 19:35
  • $\begingroup$ @darthpixel Doesn't make any functional difference in normal use whether V+ or GND is switched. But it's a big safety difference. The entire heatbed circuit is always energized with respect to ground, so any short to ground at any time with the system powered will cause Bad Things. If you switched V+ instead, the heatbed would be safely grounded and inert when not actively being heated by the controller. $\endgroup$
    – Ryan Carlyle
    Apr 21, 2016 at 21:20
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    $\begingroup$ Hello @zkent, I noticed your question has been up for a while now. Have any of the answers below been able to solve your question? If so, would you mind accepting the appropriate answer. If not, what is missing so that we may help you further? Also, if you have figured it out on your own, you can always answer and accept your own solution. Thank you. $\endgroup$
    – tbm0115
    Feb 27, 2017 at 15:50

2 Answers 2

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What happend was short circuit of course. There is no doubt you overheated HB so copper detached from HB base plate. Because you wrote it doesn't work it means copper tracks are broken.

There is very low chance to fix it. I mean it - near to zero.

What you could do is:

  1. Detach HB from arduino
  2. Find a place where track is broken (which needs to uncover it from protective layer)
  3. Connect it with a wire

Unfortunately even if you do it and your HB will work (electrically) your fixed HB which won't be flat anymore.

So definitely it's to be thrown away.

[edit]

I just realised you have double power HB, which means your HB has 2 heaters... which gives a bit hope.

take a look here

enter image description here

here is schematics which could give you an idea

You could check if your second heater works ok

If yes then you are salvaged! :)

[edit2] I really suppose the schematics of HB is more or less like this

enter image description here

So if H1 is broken there is a chance to use H2 connecting pins respectively

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  • $\begingroup$ Isn't that track only for the sensor in the middle? On the other side of the pcb, at the end of those tracks is the thermistor. $\endgroup$
    – zkent
    Apr 21, 2016 at 11:30
  • $\begingroup$ @zkent My understanding of this circuit is that there are 2 heaters. #1 between pin 1 and 2 and second between pin 1 and 3. It means pin 1 is common. One of these heaters is broken so try to use second pair. (pairs are 1-2, 1-3) $\endgroup$
    – darth pixel
    Apr 21, 2016 at 15:20
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    $\begingroup$ It will still be flat after the repair if you remount it with the heating tracks on the bottom. That will also help spread out any localized heat difference from a bypassed section. $\endgroup$
    – Chris Stratton
    Apr 22, 2016 at 2:11
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Yes, it should be possible to fix, although you might choose to replace anyway on the basis that the repaired bed might give you concerns about how long it will be before your repair fails.

You will need to carefully remove the protective layer to expose the heating element (assuming you can identify where it is likely to have broken). Then carefully solder across the break (maybe with a short fragment of wire).

After making the repair, you should cover the exposed track. This provides both electrical and thermal insulation. In the absence of any suitable high-temperature paintable covering, you could try using kapton tape.

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