Dr Seamus LED question

[Billy]

*I’ve somehow managed to accidentally delete this post whilst answering

Aplogies Dr Seamus god knows what I did

Anyway here’s the answer I was trying to post

You’re correct S4 and S6 ground the 2 colours if a bi colour LED is used

S4 would connect to S5 (ground) in effects mode illuminating one colour

With S6 connecting to S5 in bypass mode illuminating the other colour

So as you say using a single colour standard LED you can ignore S6

Again apologies it’s the first time in many years on the forum I’ve accidentally deleted a post

[Dr Seamus]

Ok cool. Thought I had removed it somehow!

Removed the lead from S6 to pad 6… getting sound in bypass and when engaged, but the LED still refuses to light.

Got out the DMM and did a diode test by connecting + to the center pad on D2 and – to the one on the right (non-white) and the LED lit up. So I managed to get that part right.

S4 is the blue lead connected to pad 4, S5 is the yellow one connected to pad 5. Cleaned up things a bit with some isopropyl alcohol to make sure i’m not getting a short around that area.

I’m probably missing something painfully obvious here, so I appreciate all the help.

[Billy]

That should work check on the LED legs you get continuity from R8 left side to LED anode and cathode to ground put your meter probe on the actual LED legs / pins

Also check voltages on both legs and the left side of R8 is it just a standard colour LED you’re using and not ulra violet or something with a higher forward voltage

Check you get continuity between 3PDT lugs 4 and 5 in effects mode

It could of course simply be a dry joint you can’t always tell visually if you have one I’ve had nice shiny joints that were dry

*edit just noticed you’ve got heatshrink on the LED legs  just try reflowing R8 joints, the LED pads, pads S4 and 5 and 3PDT lugs 4 and 5

[Dr Seamus]

Fought with this thing for awhile last night… reflowed all suggested joins, cleaned up the board again for any potential stray flux… still getting the same result.

It’s a clear white 3mm LED, which i believe has a forward voltage somewhere around 2.75 – 3v. Dunno if that would be the culprit… I used a single color “warm white” LED in the GPCB BMP OpAmp project and that one lights when the circuit is engaged. Although I used one of the 3pdt daughterboards in that build.

I did notice when I removed it from the enclosure (yea, I know… “rock before you box”) it would produce a loud buzz/hum rather than getting signal in bypass or when engaged. So could there be a possible overall grounding issue? I’ve done a number of boards from PedalPCB that usually work outside of the enclosure, so I’m assuming those PCB projects are designed differently.

Considering just pulling the offboard wiring and getting hold of another daughterboard, but would like to avoid if it is possible to wire with the LED directly to the PCB.

[Billy]

Check the voltage you get on the left side of R8

GPCB boards are the same as any other it should work outside the box

Hum or buzz as you say is usually a ground fault or loose wire

I would suggest continuity checking all LED  connections including the 3PDT centre pole

 

[Dr Seamus]

Getting continuity between 3pdt lugs 4 & 5 in effects mode, also getting it from left side of R8 to the LED anode pad (3k3 resistor… measured at 3.28k, so not far off). Same with LED anode to center lug on 3pdt. Voltage at left side of R8 is showing 8.96v when using a one-spot type of power adapter.

Interestingly, I cleaned between the lugs of the 3pdt with a cotton bud and some isopropyl alcohol, and then ran a screwdriver between them just to be sure. And when I touched lug 4 with the screwdriver, the LED faintly lit (with power connected to the one-spot). And when I connected lugs 4 and 7 with the screwdriver it lit up fully. I’m guessing there is some sort of grounding issue on the 3pdt? Or would this be further up on the PCB?

Dang. I think I’m close here.

[Dr Seamus]

Swapped in a new 3pdt… same result. So I’m guessing the issue is somewhere on the main PCB

[Billy]

What voltage do you get on the left side of R8 that connects to the LED anode

If you’ve got a spare LED check it’s forward voltage or you can check in diode mode on the LED pads you may not get an accurate reading in circuit but at least it’ll let you know it’s conducting in a forward direction

I initially though the LED was wired in reverse but from what you say that’s not the case

Are you saying when you short lug 4 LED cathode and lug 7 circuit out the LED lights fully?

I would continuity check your grounds try not to touch the wire ends for example checking S5 touch S5 pad and 3PDT lug 5 without touching the yellow wire

 

[Dr Seamus]

Voltage at left side of R8 is showing 8.96v when using a one-spot type of power adapter.

Gave up after an hour or so and swiped one of the GPCB 3pdt daughterboards from the Super Drive 70’s build that I had planned. Got that all wired in and the LED lit up as expected. Guess I’ll be sure to pick up a few more for the other GPCB projects I have upcoming.

Thanks again for all of your help, Billy!

[Author]

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