Replacing On/Off LED in Mod50 head. QUESTION

[RockStarNick]

Hey guys,

This weekend, me and Matt (EWSEthan) are going to take apart his Mod50 head to replace the on/off LED.

Correct me if I'm wrong, but LEDs are directional, right? The two metal feet aren't interchangeable.

How do I know which metal foot is which?
What side goes into where on the circuit board.

 

[Fallout Labs]

yes.. there's a + and - side of a led.

if you have a multi meter, i'm sure the negative side of the led ground to chassis (at somepoint) so whatever side of the currently installed LED provides a ground path (touch the leg of the led with one probe, and the sleeve of the input jack with the other probe) and one should provide a connection.. thats the negative (cathode) its usually the shorter of two legs.

 

[RockStarNick]

Booyah. thanks Casey.

 

[Gino]

if you have a multi meter, i'm sure the negative side of the led ground to chassis (at somepoint) so whatever side of the currently installed LED provides a ground path (touch the leg of the led with one probe, and the sleeve of the input jack with the other probe) and one should provide a connection.. thats the negative (cathode) its usually the shorter of two legs.

This isn't necessarily true although it most likely is. In order to light an LED you need power, ground and a current limiting resistor. This could be in two configurations:

1) V+ --- R --- |>| --- GND
2) V+ --- |>| --- R --- GND

The LED is the --|>|-- with the anode (+) on the left and the cathode (-) on the right. There are actually more ways to do this if an IC is involved in the circuit but let's assume there isn't as this is an amp and Bruce most likely designed it straight up in one of the two scenarios above. Chances are Casey is right but I just wanted to point out that there's a possibility that he might not be. If scenario 2 is the case you'll see some impedance between the cathode and GND so it may not necessarily be a dead short. I realize I've just complicated matters here and I'm sorry but I just want the information to be complete because there's more than one way to skin an LED.

Also, if you're changing the color of the LED, you may need to change the current limiting resistor in order to get the same brightness as before. Again, sorry to complicate things but it is what it is. A lower resistance will make the given LED brighter. Too low of a resistance will burn it out as it isn't doing its job by limiting enough current.

All of that being said, I'm sure if you ignore this post it'll all work out fine. Good luck and post your results.

 

[jkdsteve]

yes.. there's a + and - side of a led.

if you have a multi meter, i'm sure the negative side of the led ground to chassis (at somepoint) so whatever side of the currently installed LED provides a ground path (touch the leg of the led with one probe, and the sleeve of the input jack with the other probe) and one should provide a connection.. thats the negative (cathode) its usually the shorter of two legs.

a lot of LEDs have a 'flat spot' on that side too...so you can tell which is which that way.

 

[Deleted member 3860]

...

 

[RockStarNick]

Ah, nice... that flat spot is gonna help out for sure. Thanks guys!!! you rule.

 

[Fallout Labs]

Ah, nice... that flat spot is gonna help out for sure. Thanks guys!!! you rule.

i checked my leds at home, NONE of my 3mm's have this flat side you speak of

 

[bruce egnater]

email Jeff your mailing address. We can send you an LED assembly that just plugs in. FYI, yours is the only one I've ever seen fail. Lucky you...

jeff@egnater.com

 

[jmgman69]

email Jeff your mailing address. We can send you an LED assembly that just plugs in. FYI, yours is the only one I've ever seen fail. Lucky you...

jeff@egnater.com

now go buy a lotto ticket Matt

 

[EWSEthan]

email Jeff your mailing address. We can send you an LED assembly that just plugs in. FYI, yours is the only one I've ever seen fail. Lucky you...

jeff@egnater.com

Done, thanks Bruce!

 

[Jeff Hilligan]

you will have to wait due to the fact you didn't just call me or email me in the first place. Now Bruce almighty has posted and been taken away from working on stuff I need him to get done...surfing the web doesn't get business done. So rickme you are on my list! Oh by the way I will send you the led harness and a new midi chip.