Bed LED not on (but heats)
My light on my heater bed hasn't worked from the day I assembled the printer. I've swapped the polarity on the wires and still no light.
I have a multimeter out ... I've gently pushed on the resistor and diode in case it was a bad solder. I've measured 2K across the resistor (which disagrees with the schematic on github https://github.com/prusa3d/Heatbed_MK52_magnetic/tree/master/24V_05d , but aren't I also measuring the bed's resistance?)
How else can I troubleshoot this? I'm an electronics novice ...
How can I double check the diode is installed correctly? (I know swapping the polarity should have already checked that...) I naively used the diode mode in my multimeter and got 0.54v on both sides of the led -- but I'm doubtful that's a valid check since it is still in the circuit and the bed is a large resistor.
Re: Bed LED not on (but heats)
Turn on the heat bed and check the voltage drop over the diode. You will also see the correct polarity.
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Re: Bed LED not on (but heats)
I've already tried swapping the polarity of the inputs.
I'm pretty sure the led is dead, but can't figure out how to prove it since it's already in a circuit. I'm measuring 2k ohms across the diode (both ways) ... Which I think means it is busted since I'm basically measuring the resistor. I would expect that I would get really high ohms at least one way from the directional diode resistance.
So the next question might be is where can I get a similar smd led? What are it's specs?
Edit: wait.. no ... How does it make sense I get 2k across the diode? Oh because the heatbed itself loops it back around...
Re: Bed LED not on (but heats)
Again.... Turn on the heat bed and measure the voltage drop with correct polarity on the LED and the resistor. Everything is labeled with + and - , no need to swap or change something. Just do it right.
Let me know which values you're getting.
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Re: Bed LED not on (but heats)
24v is what I measure across the resistor and led ... Same as I get across the leads.
Edit: I am measuring from the upper left to lower right of the components. I mapped them out earlier looking for 0 ohm connections.
Re: Bed LED not on (but heats)
Here's a nice macro shot.... looks like the cathode dot is on the bottom, which does connect to the negative (I know the cable looks red in the corner, but it's the red stripe on the black cable -- it's negative.)
Re: Bed LED not on (but heats)
Please measure the resistance of the LED. I assume it's shortening. R1 should be 2k in your case.
Just for better understanding. This are the expected values:
Btw: This one should fit as replacement, if needed. But double check the measurements, please.
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Re: Bed LED not on (but heats)
The resistance across the LED is just under 2K. In fact, it's 1.997K ... which is pretty consistently 3 ohms higher than me measuring the resistor in isolation. I assume this is the bed's 3 ohms in series.
Re: Bed LED not on (but heats)
I just ran out to Halted/HSC to see if they had any SMDs ... I came back with a couple of things to try. I think one is an 8085 and one a little bigger.
Re: Bed LED not on (but heats)
Success!
It may not be the best looking SMD soldering job ... but it's my first second, and it's done.
Thanks Nikolai for the help troubleshooting.
Re: Bed LED not on (but heats)
Congrats! Problem solved 🙂
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Re: Bed LED not on (but heats)
I just ran out to Halted/HSC to see if they had any SMDs ... I came back with a couple of things to try. I think one is an 8085 and one a little bigger.
Got a p/N? Mine burned out at about 4 months. I'd like to try some soldering.
Re: Bed LED not on (but heats)
I believe it should be 0805, not 8085. I am going to get a replacement for mine today so will confirm.
EDIT: Confirmed, 0805 looks to be the same as the original.
Re: Bed LED not on (but heats)
I believe it should be 0805, not 8085. I am going to get a replacement for mine today so will confirm.
EDIT: Confirmed, 0805 looks to be the same as the original.
where are you ordering from?
Re: Bed LED not on (but heats)
I believe it should be 0805, not 8085. I am going to get a replacement for mine today so will confirm.
EDIT: Confirmed, 0805 looks to be the same as the original.
where are you ordering from?
for anyone else looking:
https://www.ebay.com/itm/0805-SMD-SMT-LED-Red-Green-Blue-Yellow-White-Orange-Purple-7Colours-Light/272173424833
100 red 0805 -- 0.99¢ free ship from China.
same from usa shipper? $5
https://www.ebay.com/itm/0805-SMD-SMT-LED-Red-Green-Blue-Yellow-White-Orange-Purple-7Colours-Light-UE/232682281662
Re: Bed LED not on (but heats)
Mine is also dead on boot. i did hear a pop when my Bed was test heating for first time. i'm assuming it may had something to do with the light because everything else works fine.
Re: Bed LED not on (but heats)
Sorry about that everyone -- yes, it's 0805. I fixed it on my facebook post in the mk2/s/3 group, but forgot to fix it here.