Flashing LED on the Boss TR-2 with ticking noise

[Elijah-Baley]

Hello, I have a Boss TR-2 of a friend of mine to mod. I replaced some caps, I added a gain pot to boost it a bit, and I included a toggle switch for the ultra Speed mode. Everything was ok.



I wanted to add a bi-color blinking LED: Green in bypass, Red when it's on. And I did!
Like a mod I seen, I got the voltage on the positive common on the bi-color LED from R27/ pin 7 if IC3B. The red side ground stay like the original, in P3. The only problem was that with the LED I lose some sound. A 390R resistor made the LED just slightly less bright but I solved this issue. It flashes smooth and well.

I found a right spot even for the green side ground of the bi-color LED that didn't stuck the switching system. (Then I cut the wire to try to solve my problem). Everything worked ok until the pedal is closed.

The problem is that the flashing LED introduce a ticking noise that I can heard just if I close the pedal with the back plate. It's not a contact of some parts under it, or some other parts pressed against something else: it's right the back plate, once it closed the pedal and it's in contact with the ground the ticking starts. I tried to isolated it with some tape around it, and around the screws area inside and outside, it could work if I did it good, but it's not easy nor fine.

I found this problem pretty weird.

How I can make this flashing bi-color LED work?

[antonis]

Maybe use a common Cathode bi-colour LED..??

edit: Don't mind.. Forget it..

[Elijah-Baley]

This is the schematic with the Rate LED with the instructions I followed:



https://bounav.wordpress.com/2009/03/22/boss-tr-2-rate-led-mod/

«1) De-solder the "check" LED connections P2 and P3.

2) Replace the old LED with the 3mm bi-colour but keep the old LED to hand (You can remove the old LED from the small PCB and solder two legs of the bi-colour in its place – I found I needed to file a small slot out of the plastic spacer that holds the LED off the board to fit round the third leg of the bi-colour).

3) Connect the output of IC3B (J2 or 3 depending on your board) to a 680 ohm resistor.

4) Connect the other end of the resistor to the anode of the old red LED.

5) Connect the cathode of the old LED to the anode of the bi-colour LED. Make sure that the connection of the old LED and resistor are insulated with heat shrink or electrical tape.

6) Connect the red cathode of the bi-colour to P3

7) Connect the white cathode to jumper J15 (that's on the rev1 board – it appears to be J21 on the rev 2 board).

Explanation of the cathode connections: P3 is where the original check LED cathode was connected and goes to the collector of one of the transistors (Q5) that makes up the bistable circuit that controls the effect bypass/on switching circuit. J15 is the collector of the other transistor (Q7) in the bistable.

Why keep the old LED? I used the old red LED in my circuit (wrapped up with the 680 ohm resistor inside the pedal) to drop an extra 1.8 volts so that the LED flashed properly.»

The only thing I changed is the resistor. The instructions indicated a 680R, but for my LED that was too much and the LED light was too weak. So I used a 390R. Then I omitted the old red LED, too, because, the instructions says that it's been used to drop extra volts, but I didn't need it, as I said.
The flashing and the light was good. Was the LED necessary to cut of the ticking?

[antonis]

I'm not sure I can get you..

Do you want the Red LED to blink with effect bypassed..??

[Elijah-Baley]

Look at the schematic. The LED is a bi-color, R is for Red and G is for Green.
The oscillating voltage is in the positive of the LED, that makes the flashing the LED always.

The two negative side of the LED, the Red side goes where the original LED was, the pedal engaged. The Green side goes in the opposite side of the swithing, that make (flashing, of course) when the pedal is bypassed.

That works perfectly. I just I can't get how the ticking starts when I put the back plate in contact with the box.

[antonis]

Look at the schematic.

Sorry but I suffer from impaired perception..
(I was just trying to associate your issue with different grounding routes..)

P.S.
I'd try a non-conductive material (wood, hard plastic, plexiglass, etc) for back plate to find out if the issue relates with items/wiring squeezing..

[Elijah-Baley]

I have no issue if I press the board inside the box, but when I put the back plate on the rear of the box and make it in a fuller contact it's ticking. I tried to isolated it, but it's not simple. Considerate there's the screws, too. Through the holes of the back plate touch the box in the screw "housing".

I'm not able to replace the back plate with other material plate, I can't do that kind of work. And well... I prefer to keep the grounding cage, though when the pedal is open it's not noisy.

I think that blinking method is already verified, maybe should I try to add a diode in line with the 390R resistor? (A bit like Boss do with R17 - D5?)

[idy]

The original modder suggested adding the old LED in series with the new one to drop voltage, like your diode idea but more. Did you follow that? Is your LED plenty bright? How much could you dim it before it made you sad to look at it?

[ElectricDruid]

I have no issue if I press the board inside the box, but when I put the back plate on the rear of the box and make it in a fuller contact it's ticking. I tried to isolated it, but it's not simple. Considerate there's the screws, too. Through the holes of the back plate touch the box in the screw "housing".

It seems highly unlikely that the problem is the back of the box being on. The question is whether the back of the box is shorting something when it's in place. Testing that is as simple as sticking a bit of plastic between the PCB and the lid before you close it up. Overhead transparency sheets are good for this, if you can find any of them any more! (I have a stack I stashed for this job!)
Basically, I can't see any way *more shielding* for the circuit increases the ticking. I can see plenty of opportunities for random shorts to do that.

[Elijah-Baley]

The original modder suggested adding the old LED in series with the new one to drop voltage, like your diode idea but more. Did you follow that? Is your LED plenty bright? How much could you dim it before it made you sad to look at it?

My LED is this one:

(But my LED has the common anode (positive), it just doesn't the image.)
It doesn't bright so much, so I used a smaller resistor and I had no reason to use the old LED to drop the voltage (and take more space inside the pedal).

The why I said the ticking is caused by the back plate grounded is because if I press the circuit with my hand I have no ticking. Don't forget the Boss pedals have a plastic sheet between the solder side and the back plate. I exclude contact of the back plate.
The things gone better when I tried to isolated with the tape the border of the back plate, and, even if the back plate was well pressed, I didn't have the ticking.
But when I put on it the screws, one was enough, that put the back plate in contact with the ground again.
It was a bit better when I put the tape around the screws area, but it's not easy isolated the screws from the back plate, and when the screws are too much tight on the back plate the ticking starts.
This is the reason I said, though it is very strange, grounding the back plate is the cause.
Maybe I didn't told it, but the ticking is just when the effect is on.

I'm waiting some clue about the adding the LED or a diode (1N4148?) after the 390R resistor stop the ticking before to try it.

My other mods was a pot in series with the R12 resistor, and a switch spdt change R31. In both the case I can get the original values when the pot is at zero and the spdt is set at one of the side.
Anyway, with the pedal open I got no ticking.

[Elijah-Baley]

Hello.
I tried to include the diode, the original one, the one where in the schematic is marked with an x. The 390R and the LED are in inverted order, but I guess is the same. Anyway, that didn't solve.
It's enough lay on the rear the back plate, not necessary all the portion, but even partially, and the ticking starts.