Celica Forums General Discussion Exterior Electrical Experts...

Ok, I think I soldered in my LED's in backwards, and before I go in and reverse the polarity, answer me this question...

In the picture below, is a crude drawing of the "T" symbol on the back of a surface mount light emitting diode. I'm having some trouble intreperting it.

Bastards...

Sons a bitches...

If you have access to a volt meter you can use the diode checker function to test the LED for polarity.

Well generally your Anode is your "longer" terminal of your LED also the positive.

Also from your drawing I would assume that it is anode->cathode because a typical diode symbol is --|>|--

It's a surface mount LED meaning that it doesn't have prongs as terminals.


And yeah, I did do a test with a voltmeter, and found out that I did have them on backwards.

But I still have a problem...


I changed a few around to the correct way that they should be mounted, and went back and tested it in my car expecting to see only those few light up.

Wrong. None of them are lighting up still.


I wonder if it's because they are all along the same circuit, and they have to all have the same polarity, or perhaps it's because at the bottom of the board, I'm missing two LED's due to the fact that on the board on one side, one of the mounting pads is missing, so I just left out the LED on that side, along with the LED on the other side so it would look like it's supposed to be that way.


Anyone know if this is perhaps why none of them are lighting up? Because two LEDs are missing?

Yes the LED's are connected in series of 2 or 3 so if one is reverse polarized the other 2 or 3 on that circuit wont work. So what i did to test this was only unsolder 1 LED and replace it with 1 new blue LED, if it didnt work i had it in backwards. I just found this out last night because i was doing the same thing. What i found to be the easiest is to look at the front of the surface mount LED and make sure the little square in the clear part, called the die, is pointing to the bottom of the gauge circuit board. This is of course if you are using blue LEDs, if they are red however the die should be at the top.

Gotcha, thanks.


Even when I reversed the direction on some of the LEDs, they still won't light up. Could it be the fact that I'm missing two LED's on the very bottom of the board?

I believe those two light up the hole in the tape deck.

If the LED's weren't there from the factory, dont add extra ones, but if you de-soldered some and didn't re-solder in a new LED it would be the same as having one reverse polarized, the rest of the LED's in that series wont turn on.

There were two LEDs there from the factory. The reason I didn't put them in is because I damaged one of the mounting pads, and I left the other one out because it was coupled with the other one.


And none of the LEDs light up, so I guess this is near the source of the power, and I broke up the circuit?

Like I said in another post, theres many pathways in the circuit they could go. I'll assume that all the LEDs are on the same pathway.

Simple circuits, rule of thumb is if you have an open cicuit, nothing will happen. If there were LEDs in the two open ones, you should replace those or replace them with equally impendent resistors (keep the current the same). Make sure they are all polarized and check you solder connections. It took me a long time to realize that I needed flux with the solder I purchased.

If anything else, you could have burned one of the LEDs out. They're strong buggers, but it happens sometimes. Good luck and keep us informed.