Big muff - tone pot acts like 2nd volume pot

[chromesphere]

Hi all,

I built a big muff pi (tonepad) standard version about 12 months ago.  Its been a great pedal.  I hadn't used it for a few months, plugged it in the other day, and found the tone pot was behaving oddly.  Its not acting like a tone control anymore, and as i adjust the pot, it lowers and raises the volume.  The actual tone sounds pretty bassy and stays that way no matter where the tone pot is set too.

It sounds like its working, the distortion sounds as it should, i just cant change the tone, seems to be 'stuck'.  I swapped the 4 transistors for new ones (as a stab in the dark) but this didnt help.

Not sure what voltages to look for, heres a start:

Tone Pot CCW (if your looking at the tonepad schematic, reading right to left)

1) 1.54v
2) 3.22v
3) 3.22v

Tone Pot CW (same as above)

1) 1.54v
2) 1.54v
3) 3.22v

Q1
E) .03v
B) .61v
C) 3.85

Q2
E) 3.85
B) 0.61v
C) .03v

Q3
E) .03v
B) .61v
C) 3.82v

Q4
E) 1.18v
B) 1.7v
C) 3.54v

Hope i got those E B and C's the right way around.  Xmas parties will do that! :-)

Thanks for any help.  Any suggestions are greatly appreciated!

CS

[anchovie]

Reflow the solder joints at both ends of the wires that connect the pot to the board.

[chromesphere]

Hi Anchovie,

Thanks for the suggestion.  Even though it didnt fix the problem directly, while I had the pedal apart, i resolder some rather dodgy joints on the PCB (hey, it was the 3rd pedal i built, give me a break  ), and checked everything over.  After a bit of tinkering it just decided to start working again.  Whatever i did, seemed to fix it.

Thanks for prompting me in the right direction  

CS