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I'm soldering, couple of questions.

Posted by GAZ082 
I'm soldering, couple of questions.
November 16, 2013 03:33PM
Hi there. Im soldering my RAMPS board. A couple of questions:

1. How do i check the capacitors are properly weld? So far, welded one and there is no continuity sound, but not sure if should be, it's a capacitor after all...
2. Tested a mounted led, there is continuity but the led does not turns on like the rest of the board, is it burnt?

Thanks!
Re: I'm soldering, couple of questions.
November 16, 2013 04:01PM
With capacitors, they don't show continuity. Your best bet is to check the continuity between the pad and the track you're soldering it to, and that the solder joint is shiny. Also, if they're the little can type ones, make sure you get them the right way around as they're polarised (usually marked with either + and -, or the minus side is marked with a black strip).

With LED's, they're diodes, which are also polarised. Continuity checks on a multimeter may not light an LED up (may not have enough voltage). If others do light up but not this one, then you may have it backwards (easy with such a tiny component). You can test that by simply reversing your test leads.

FWIW: A simple test for the polarity of a LED is 2 x AA or AAA batteries in a small battery holder, and a small resistor of about 180 ohms. Connect the red lead on the battery holder to the resistor. Then connect the LED between the other end of the resistor and the black lead of the battery holder. If it doesn't light up, reverse the pins on the LED. Once it lights up, the pin on the LED connected to the resistor is the Anode (triangle side of the schematic diagram) and the black lead is connected to the Cathode (the bar side of the schematic diagram, and usually marked on the PCB as a bar).
Re: I'm soldering, couple of questions.
November 16, 2013 05:03PM
You can also use the "diode" function on the meter to illuminate those surface mount LED's.


_______________________________________
Waitaki 3D Printer
Re: I'm soldering, couple of questions.
November 16, 2013 05:11PM
Thank you guys. I think the moment of truth with the caps will be when testing the board fully assembled. The caps are SMT.

Regarding the LED, i'll remove it and weld again, checking the dots. But even though i reversed the probes and give me continuity, the LED still does not turn on. I think it's dead, will replace it in the future.

EDIT: realized that i wrongly weld the LED in another track, these boards are so tiny! Now its working. smiling smiley

Edited 1 time(s). Last edit at 11/16/2013 05:20PM by GAZ082.
Re: I'm soldering, couple of questions.
November 16, 2013 06:19PM
Quote
waitaki
You can also use the "diode" function on the meter to illuminate those surface mount LED's.

I've got a few meters that disagree with you on that front. :/
Re: I'm soldering, couple of questions.
November 17, 2013 07:00AM
A very nice thing to have around - a little lab grade power supply with meters.

You can get these pretty cheap on the auction sites. The cheap ones don't put out a lot of current, but you aren't going to use them for a 10A gizmo. What they do:

1) The show you the current being pulled on a meter (so you can unplug things fast).
2) They let you set a current limit with a knob (so you don't put a lot of current in)
3) They show you the voltage on a meter
4) They give you a knob to slowly adjust the voltage.

Much less stress powering up your new board with one of those than just plugging it into a 12V 30A supply.
Re: I'm soldering, couple of questions.
November 17, 2013 08:25PM
Quote
Cefiar
Quote
waitaki
You can also use the "diode" function on the meter to illuminate those surface mount LED's.

I've got a few meters that disagree with you on that front. :/

Strange? I have 3 meters that all light up the LED's - maybe it only works on certain types?


_______________________________________
Waitaki 3D Printer
Re: I'm soldering, couple of questions.
November 18, 2013 09:33AM
Some meters are set up to source a very small amount of current in diode test mode. The idea is to not harm a very low current part. If you have one of those 100's of ua limited meters, it's not going to give you much light out of the LED.
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