MKC3 was working, problem with the LED

[seagurt]

I had put together a MKC3 build (mini Klon circuit, based off the Aeon Archer) and it was working great. I decided to add a 3pdt switch and wire the resistor pads (R15) with off board wiring, leading to the 3PDT middle lugs, and adding my resistors to the top and bottom lugs (one 47k, and one 8.2k). I also ordered an anode bi color LED and installed it.

When I plugged it in, no sound, bypass is fine, the LED doesn't light up.

When I was poking around, checking board voltages, things looked good, 9.59v to the circuit. I probed the positive of the pad for the led, and the blue light came on. I probed the middle, nothing, and the third one produced the other color (red in this case). I am wondering why the LED isn't turning on when I hit the footswitch.

The diode before the LED reads full 9.59vDC.

Perhaps I am missing something glaringly obvious to someone here?

The build document can be found here...

http://www.guitarpcb.com/PDF%20Files/MKC3.pdf

Unfortunately, I cant find a schematic for this particular circuit.

I can add pictures if you want them, just let me know what you need to see.

Cheers!

[antonis]

A draft diagram of LED wiring to 3PDT switch should be helpfull...

[seagurt]

A draft diagram of LED wiring to 3PDT switch should be helpfull...

I thought this particular build dealt with switching on the main board (for the LED I mean, I understand the switch needs to be engaged to let the signal pass through the other lugs). d3 indicates the component can be on the PCB, but perhaps I am missing something, like getting the voltage there...

Here are some pics. D3 has 3 wires coming from it, near the daughterboard for the 3pdt.





Should I be adding another wire from my 9vdc to one of the 3pdt lugs?

[antonis]

I decided to add a 3pdt switch and wire the resistor pads (R15) with off board wiring, leading to the 3PDT middle lugs, and adding my resistors to the top and bottom lugs (one 47k, and one 8.2k).

Sorry but I can't follow you... 

LED current limiting resistor is R25 (3k3) - not R15 (47k).

R25 has to be connected to +9V and LED anode (LED cathodes to 3PDT middle lugs 4 & 6 - 5 to GND )..

[seagurt]

I decided to add a 3pdt switch and wire the resistor pads (R15) with off board wiring, leading to the 3PDT middle lugs, and adding my resistors to the top and bottom lugs (one 47k, and one 8.2k).

Sorry but I can't follow you... 

LED current limiting resistor is R25 (3k3) - not R15 (47k).

R25 has to be connected to +9V and LED anode (LED cathodes to 3PDT middle lugs 4 & 6 - 5 to GND )..

The resistors on r15 are for the gain mod. I know r25 is for current limiting the resistor, perhaps I should have specified that. My bad.

I am still confused as to why its not working on the board, I am getting voltage to the LED (mind you its under a volt, and I know a LED doesnt require full 9v, it just burns).

I will try wiring it up the way you propose, and see what happens.

Thanks

[antonis]

I am still confused as to why its not working on the board, I am getting voltage to the LED (mind you its under a volt, and I know a LED doesnt require full 9v, it just burns).

An LED needs current rather than voltage to work (after all, it's just a (photo)diode..)
When working under proper current flow, it "appears" a voltage drop between its anode & cathode (strongly depended on its colour..)

I mean that a voltage difference between its legs isn't the cause for working but the result of its function..!! 

In your case, the low voltage drop between LED anode and cathode (in case of R25 connected right) indicates not enough  current flowing through LED..
(I should blame R25 resistance value for that..)

[seagurt]

In your case, the low voltage drop between LED anode and cathode (in case of R25 connected right) indicates not enough  current flowing through LED..
(I should blame R25 resistance value for that..)

So should I be replacing the resistor value with something else? Something lower?

Also, should I still add the LED to the 3PDT footswitch? Should it be in this layout? Minus the resistor?


Perhaps you can enlighten me on something I have been wondering in regards to this build.

Why, or what is the reason for it working perfectly fine before I added the LED. Is this normal, that without the LED, it operates as intended, but including the LED, with regards to current, and my failure to get it to operate as it should, there is no sound coming through the circuit output?

Thanks again, I have already learned something!

[duck_arse]

any circuit that can't survive the addition of a correctly wired led indicator circuit has some other problem (possibly introduced whilst adding the led addition).

your diagram is the thing to do, if you have a common cathode bi-colour led. common anode would see the led reversed, and the two supply connection swapped, no other changes. as diagrammed, you would expect to see 9V at one end of the resistor, and 1V7~2V2 at the other end of same. and light, emitting.

which is more important, fixxe first - audio or indicator?

[seagurt]

any circuit that can't survive the addition of a correctly wired led indicator circuit has some other problem (possibly introduced whilst adding the led addition).

It turns out that my dc jack from the wall wart has some issues, a break in the wire. I make a habit of testing the jack when troubleshooting, seems when i was testing, the current was flowing, but when I moved the stompbox, it stopped. The effect works, and I dont think it ever didn't work, beyond my dc jack issues.

I may just end up throwing a normal LED indicator on this one and be done with it.

Thanks again for the helpful replies.