Dead Big Muff Pi v9 (NYC)

[Jrm]

Had a buddy drop off a few pedals that aren't working, and one of them is a Big Muff Pi reissue with the EC3003-A board inside. When engaged, there's no signal and the red LED doesn't come on. I checked all the connections and nothing's loose. All the solder joints look good, none of the caps look swollen, and I can't find anything that looks weird.

Does anyone have experience with this particular pedal, or have an idea of where I can find a schematic with voltage measurements? I've been searching, but keep finding the same schematic that lists components, but no test points.

Thanks in advance to the group for any/all help/advice.

Cheers,
Jrm

[g1]

Can you post or link the schematic you are looking at? Does it appear to be correct for that version?

[Jrm]

Here's the link. The schematic is at the very bottom of this page. It appears to be accurate.

[g1]

Where?

[Jrm]

Whoops! Sorry about that.
Here's the link: Big Muff Pi Versions and Schematics

[52 Bill]

Are you using a battery or an ac adapter?

[Jrm]

Tried it with both and got nothing.

[g1]

I guess you could start by measuring transistor voltages and posting the results.

[Mark Hammer]

It would help if we knew something about what happened before it stopped working.

That said, make sure that +9v is actually reaching the board. The fact that the status LED doesn't come on suggests there is an issue with the power. Hopefully, nobody attempted to do a bad job either changing the power jack, or re-attaching the battery snap, and connected leads to the wrong places.

[Jrm]

The owner mentioned that he had to re-solder one of the leads to the DC plug itself, but doesn't recall which one. It appears to be wired up correctly, and if it was just one wire I don't see how he could have messed that up, but I am noticing that it's not your typical "negative-center" power supply that I find on almost every guitar pedal. It's got the positive lead of the battery connected to its switch, rather than the sleeve, and the negative lead of the battery wired to the switching jack on the signal input. That seems odd.

And I ran my meter (in diode test mode) over all four transistors with the pedal disconnected from any power source, and all four of them gave me an average of .654 on all +B-C and +B-E connections, but I got "OL" on all other readings.

[g1]

Sounds like it just got re-wired wrong. That's assuming you verified the AC adapter/supply is working.
Unfortunately the schematic doesn't show much of the power input.
The switch on the DC jack is so the battery gets connected when the adapter is unplugged, and battery is out of circuit when adapter is in use.
The grounding through the input jack is so when you unplug your guitar cord, the battery is disconnected and does not drain.
If you can take some pics of the input and DC jacks, and where their wires go, that would help.

[Jrm]

My first thought was that is was re-wired incorrectly as well, but if he only re-soldered ONE wire, that doesn't seem possible.

Here's a photo. Let me know if you would like another.

[52 Bill]

As best as I can tell, your photo shows everything correctly. The adapter jack is a 1/8" mono phone jack, tip positive. The battery clip negative goes to the ring contact on the input jack for battery switching.

If you test this with a battery, it will need to be reinstalled into the case as the grounds are not connected without it.

[Jrm]

But in theory, it should work correctly with the power supply connected? I'm not sure where to go from here.

[Mark Hammer]

Ah, one of "those".

Because of how they have to do the switching (pushing a contact out of the way), whenever insertion of a plug is used to disable the onboard battery, and revert to external power, ALL such appliances that use negative ground, will have tip-pos for phone plugs, and outside-shaft pos for barrel-type plugs. Some folks will naively assume that tip for the one implies tip for the other. Nuh-unh.

If the battery connector and power jack is wired up right, when there is nothing plugged into the power jack, you should get continuity from the positive contact on the battery snap to wherever the red wire connects to on the board. If that isn't the case, then the chances are very good you need to flip the connections of the two red wires soldered to the power jack.