Magnetron Delay LED2 issues

[falco_femoralis]

Hi all, I'm having trouble getting the modulation LED to work. I've switched around the current limiting resistors a few times and have a feeling I fried a solder pad, but I'm having trouble reading the diagram in order to trace the circuit board. I've played around with the depth control and no matter where it's set the LED doesn't come on.

The diagram says LED2 gets its current from its CLR, which gets its current from the LFO. Where does that come from?

On the diagram there's an LFO in a triangle just after pin 2 of the Depth control. Is this meant to be where LED2 gets its current from?

My board doesn't have continuity between the solder pad of pin 2 of the Depth control and the forward side of the LED2 CLR and I can't check this guess.

Thanks for any direction

 

[falco_femoralis]

okay so I pulled the CLR and saw that the solder pad was damaged, and with it out I was able to see the trace from the negative pin of C8 to the right side of R103. I put in a new capacitor and used its neg leg to make a bridge across where R103 used to be. I'm moving the resistor off the board and will wire it in line with the LED, which will allow me to play with brightnesses without getting into the board. And LED2 works now, but I have a new problem.

The LED is very dim. It flashes in time with the speed knob but it is so dim it's hard to see. I got the volt meter out and checked voltage from pin 2 of the Depth pot to ground. When the pot is maxed, I get about 6v, and when it's halfway, I get about 2.2v. When it's at 9 o'clock, it's putting out about 0.8v. Way lower than the LED needs, and to get any brightness out of the LED at all, I have to use a super low 390 OHM resistor. When the pot is at anything less than halfway, I really don't even need a resistor bc the voltage is so low, and of course when the pot is at around 9 o'clock, the LED is off.

Unfortunately I don't know enough about circuit diagrams to be 100% but it looks like the LFO sees maybe 6v max due to its 120k/220k voltage divider resistors. Idk why there is a 4k7 CLR then? It doesn't make sense from what I am seeing. According to the schematic, the only source of power for LED2 is the voltage divider for IC2. What am I missing?

When I check voltage at the center lug of the footswitch and the pole just above it (facing the circuit board) I get 7.85v, but at the power plug coming in from my Voodoo Labs power supply I get about 9.3v.

Everything about the pedal works great, except for the modulation LED.

When I first put it together I wired the two LEDs backwards (thought the one up top was the modulation LED and the one near the footswitch was the indicator LED) and ended up blowing up the bicolor LED I was using. The top of it literally blew off. The pedal worked fine after as far as sound, response to all the controls etc, but I'm wondering if there's anything else I need to check that might be affecting the situation I'm in now. I am using a regular LED when testing the modulation LED circuit, and when I get this working will sort out the resistors I need to use to make the bicolor work.

 

[falco_femoralis]

Okay so I used an online calc and with a 6.5v supply with a blue LED @ 3.3v, I used 180 ohm resistor as the minimum value resistor for the modulation LED and it's working "as expected." The taper on the 100k Depth pot is terrible for the LED. It goes from nothing nothing nothing a little bit to super bright. I can use a large value resistor but as soon as the pot is backed off from full, the LED will all bit shut off. What I want is a gradual increase/decrease in brightness when turning the Depth knob.

So what I need to do is make a dual value dual gang pot out of 100k and either a 5k or 10k dual gang pots. Which is something I will have to order bc all I have on hand for dual gangs is a few A1ms (of all things) and some C100s. Awesome

 

[falco_femoralis]

While I was at it I tried a b50k and then a b25k pot as the Depth control and they both seem to do the same thing - nothing until 11 o'clock and then a very subtle modulation and then ALL the modulation at around 3 or 4 o'clock. I'm going to try a C pot but as it turns out all I have are dual gang 100k! I believe a 50k would be better but I suppose I'll try what I have and report back