Can a short-circuited heat bed be salvaged?
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?
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.
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."
@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.
@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.
@RyanCarlyle I still don't get how it influence on the case of fixing HB. The problem is not how to do it according to all possible standards but to recognize if it can be fixed (make to heat again). Nevertheless I still suppose there are 2 heaters with common pin1. This asumption is made on the table all HB has painted with (which i linked in my answer). (take a look on my [edit2])
@darthpixel Oh, sorry for the confusion, I wasn't trying to say anything about your proposed fix. Just commenting on the question -- the fact that the heatbed was "off" doesn't mean it's de-energized. It's an important safety note for people when working on the printer, cleaning build plates, etc.
This sounds like the precursor to settings ones house on fire ...
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.
darth pixel Correct answer6 years ago
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:
- Detach HB from arduino
- Find a place where track is broken (which needs to uncover it from protective layer)
- 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.
I just realised you have double power HB, which means your HB has 2 heaters... which gives a bit hope.
take a look 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! :)
I really suppose the schematics of HB is more or less like this
So if H1 is broken there is a chance to use H2 connecting pins respectively
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.
@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)
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.
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Content dated before 7/24/2021 11:53 AM
zkent 6 years ago
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.