Dead Big Muff Pi v9 (NYC)

[g1]

I've had enough shaky info from the actual owners that I still verify everything, especially if they have been in it.
So I'd still like confirmation that the 2 reds on the DC jack are going to the right places (tip and switch). Unless 52Bill is familiar enough with that type of jack to confirm from the photo.
I'm not sure from that which is tip and which is switch, and if those 2 are reversed, it will not work with the adapter.
I guess if you can measure 9V from ground to any point on the circuit board, that is confirmation enough.

[52 Bill]

But in theory, it should work correctly with the power supply connected?

I'm not sure if that is true. Are all of the ground circuits connected by wires to all of the jacks, etc.?

g1- I do know that the two connections at the end are the tip and switch, but I don't know which one is which. So, you are right, if they are reversed it will not work with the wall adapter.

[Jrm]

All continuity tests confirm that the jack is wired properly and I get 9v at the board using either battery or power supply. It's just where it's going after that which appears to be the problem. Should I try measuring voltages at the transistors?

[g1]

Without a more complete schematic, that may be the next step.
Unless you can trace out the led circuit. That might lead to something simple like a protection diode or fusing resistor.
The problem is that the led circuit, power circuit and switching circuits are not shown on this schematic.

[Mark Hammer]

I guess the next question to ask is whether the person you got it from installed a 3PDT stompswitch. There are ways of not getting a signal passing and no status LED lighting, even when the power to the board seems fine.

One of the common errors made by hobbyists and novices is that they apply far too much heat to the solder lugs. As I illustrate in this video, there is a small amount of grease inside the switch, used to both hold the rocker contacts in place during assembly, but also to minimize and dampen any "chatter" in the switches. When people apply too much heat in the installation, they liquify the grease, and it flows to cover, and insulate, the contacts. Believe me, if the failure rate among commercial buyers of these switches was anything like what hobbyists experience, the manufacturers would be out of business in no time. The problem is that people are making them fail by virtue of their poor soldering technique.

The good news is that one can successfully disassemble the switch, clean the contacts, reassemble, and have a flawlessly functiong switch; sometimes without even having to unsolder anything.

[Jrm]

I'm having a hell of a time trying to find any schematics that include the switches. It's a reissue and everything appears to be stock. No other hands have been inside this pedal (aside from the owner re-soldering one wire) besides mine. I also ran continuity tests on all the contacts of the foot switch, and there's no issue there. If anyone can nudge me in a specific direction, I'm willing to keep poking around on the board. I just don't know if I should be measuring voltages between transistor pins or from ground, or if I should just start chasing the power signal and making notes of the readings.

[Mark Hammer]

The Sustain pot provides a sort of bottleneck for the signal. If the pot is not successfully passing signal, you won't hear anything at the output. So assess continuity between the input lug and wiper of the pot.

[Jazz P Bass]

I'm having a hell of a time trying to find any schematics that include the switches. It's a reissue and everything appears to be stock. No other hands have been inside this pedal (aside from the owner re-soldering one wire) besides mine. I also ran continuity tests on all the contacts of the foot switch, and there's no issue there. If anyone can nudge me in a specific direction, I'm willing to keep poking around on the board. I just don't know if I should be measuring voltages between transistor pins or from ground, or if I should just start chasing the power signal and making notes of the readings.

The transistor voltages should be read with a reference to Ground.
All of the separate circuits are Class A.
The Collectors will be close to 9 Vdc.
The Bases should read roughly 1/2 of the Collector value.
The Emitters will be 0.6 Vdc less than the Base.

Here is a link with a few schematics: EHX? Big Muff Pi? | General Guitar Gadgets

[Jrm]

Had to go out of town for a bit, but I'm back to poking around on this pedal. The sustain pot is functioning properly, and a quick poke around the transistors gave me readings in the 100-110 millivolt range on all of the transistor collectors with the foot switch in both positions. Pressing the switch gave no change on any pins of the transistors. A short chase of the power signal gave me a reading of 9.2v at the point where it meets the board at a 100ohm resistor, and gave a reading of 4.6v after the resistor. Is that indicative of anything?

Thanks for all the help/suggestions.

[Jrm]

Anyone have any useful information? I'm completely baffled by this one and all seems to have gone quiet on the forum front...

[52 Bill]

Had to go out of town for a bit, but I'm back to poking around on this pedal. The sustain pot is functioning properly, and a quick poke around the transistors gave me readings in the 100-110 millivolt range on all of the transistor collectors with the foot switch in both positions. Pressing the switch gave no change on any pins of the transistors. A short chase of the power signal gave me a reading of 9.2v at the point where it meets the board at a 100ohm resistor, and gave a reading of 4.6v after the resistor. Is that indicative of anything?

Thanks for all the help/suggestions.

The footswitch only reroutes the audio signal, so there should not be any changes in the circuit voltages when you switch the fx in and out. The 100-110 mV readings all sound too low to me.

The fact that the voltage is dropping by half probably means that there is something that is drawing a lot of current in the circuit. Is the battery getting warm? How about the 100 ohm resistor?

[Jrm]

Nothing's getting hot, and I'm running it with a power supply. From that 100 ohm resistor it goes straight to a big electrolytic capacitor. Could that be the problem?

[52 Bill]

Nothing's getting hot, and I'm running it with a power supply. From that 100 ohm resistor it goes straight to a big electrolytic capacitor. Could that be the problem?

Yes, it could be shorted. Remove it and see if the voltage comes back up.

[Jrm]

With the 220uF cap off the board the voltage reads 9v before and after the 100 ohm resistor.

[g1]

Sounds like the cap is bad then.