Help repairing V6 Big Muff

[CozmikKing]

A little while ago a friend found a Big Muff in a family friend's basement and traded it to me in exchange for a tenor saxophone that I found in a liquor store parking lot.  It worked well for about a year, but the other day when I plugged it in it seems to have lost all of its power.  The output volume is really quiet and it's about half as saturated as it should be with the sustain cranked all the way up.  I've tried putting in a new battery but no luck there.  I do live in a very dry and hot climate and the pedal does spend most of its time in my hot garage studio.  So I'm thinking a component could have maybe dried out.  But I'm a guitarist and not an electrician so I don't know and don't quite know where to begin fixing it.   

Does anyone have any insight about how I can get my Muff back to normal?   

[Scruffie]

Probably just a bad electrolytic cap somewhere.

[11-90-an]

Welcome to the forum...
Do you have any pics of your pedal? Back and front? Voltage readings?

[CozmikKing]

I don't have a multimeter handy but if i were to have one would it be as simple as reading the voltage on every component to see if the signal doesn't pass through or read at the correct value? 

I'd love to post some pics but I've been without a working camera on my for about a year now. 

[Marcos - Munky]

For the voltages, put the multimeter on dc voltage setting, black probe on ground and, with the red probe, check the voltage on each transistor pin. Also, the dc voltage of your power supply.

For photos, a cellphone camera do a nice job.

First thing I'd check if there are any electrolityc cap that looks like those ones: https://3.bp.blogspot.com/-KAo8F-kZMoc/UkH34vbKiFI/AAAAAAAAArY/xygf1uYnVdM/s1600/fgfd.jpg
If their top is opening, you should replace them.

[CozmikKing]

Thanks for the info Marco.  I'm gonna look for that tomorrow when I open it up tomorrow.  It's safe to assume that a failing capacitor wouldn't cause total failure of the pedal but could also alter the way the signal passes through?

[CozmikKing]

Okay so I went in it with a capacitor and all the transistors seem to reading at around -3 to -5 volts which I assume is good?  The point where the positive lead of the battery solders to the board is reading at 9 volts.  Where do you think I should looking to next?  All the capacitors look good and not burned out or leaking, but maybe they're dead inside (like me trying to fix this  ).  To reiterate the issue the pedal is having, the volume and gain output of the pedal are very weak.  Perhaps there is a big muff buff out there who recommend a specific component that could be the culprit here. 

[11-90-an]

Welcome to the forum...
Do you have any pics of your pedal? Back and front? Voltage readings?

[CozmikKing]

Welcome to the forum...
Do you have any pics of your pedal? Back and front? Voltage readings?

Alright I've got the readings!  I'm new to this so i hope i got the transistors labeled correctly. When looking at the picture of the circuit board component side up they run 1-4 left to right and it seems Q4 is reversed from the rest. 

Q1
    C -3.96
    B -0.62
    E -0.03

Q2
    C -3.96
    B -0.62
    E -0.03

Q3
    C -3.81
    B -0.62
    E -0.03

Q4
    C -3.52
    B -1.89
    E -1.30

[antonis]

Although Collector voltages seem a bit low (especially Q4 collector should sit on about 6V with Emiiter on 1.3V and Collector resistor of 10k..) your pedal seems to be functional enough..

You should check (or better replace) all electolytic caps in signal path..
(they should be all 1μF cylindrical caps..)

P.S.
"Dried out" (electrolyte's water evaporated) capacitors act as signal "blocking" obstacles due to highly elevated ESR..
(big resistance set in series with signal..)

[CozmikKing]

Although Collector voltages seem a bit low (especially Q4 collector should sit on about 6V with Emiiter on 1.3V and Collector resistor of 10k..) your pedal seems to be functional enough..

You should check (or better replace) all electolytic caps in signal path..
(they should be all 1μF cylindrical caps..)

P.S.
"Dried out" (electrolyte's water evaporated) capacitors act as signal "blocking" obstacles due to highly elevated ESR..
(big resistance set in series with signal..)

Okay great thank you for the help.  I'm gonna order some caps today.  A problem I've just run into though is that I can't seem to find the right look capacitors on google or mouser or anywhere.  I thought that they were film capacitors but i can't seem to find what looks like mine.  Can you point me in the direction of the right ones to order?

[11-90-an]

https://www.taydaelectronics.com/1uf-50v-105c-jrb-radial-electrolytic-capacitor-5x11mm.html
Or
https://www.taydaelectronics.com/0-1uf-280v-100c-10-metallized-polypropylene-film-capacitor.html
These should be good for you...

[antonis]

Film capacitors shouldn't need replacement but if you wish to replace them check for proper legs spacing..

[willienillie]

What are the transistors, 2N5087?

[willienillie]

What are the transistors, 2N5087?

Looking at your pictures again, I don't think this is a PNP/positive ground Muff.  Are you really reading negative voltages on the transistors?

[CozmikKing]

oh man no I'm so bad at this.  the voltages are all positive!

I took out the 1uf cap near the Q4 transistor to test it.  I tore apart an old stereo receiver that hasn't worked in years to harvest another 1uf and viola!  it's back to it's old self.  The thing that i find interesting though is that i re read the voltages on the transistors afterwards and they're not much different, only a little bit lower than they were with the bad cap in there. 

The Q4 now reads

C 3.49
B 1.88
E 1.30

Maybe that "a little lower" is a mile in terms of how voltage works, but either way I' glad I was able to fix this.  Thank you for all for the help. 

Any chance there's something that I can do to mod a big muff to make the output even louder?  Even before the pedal broke down this is something I had wished for.  Big Muff's just don't have high enough output to slam into an amplifier like say a Fuzz Face does. 

[willienillie]

The flakey old electrolytic cap had probably been mainly a problem for AC signal (high ESR like Antonis said), and not had much effect on DC conditions.  It wouldn't be a bad idea to replace the rest of them, and not have to worry about it for the next couple decades.  If you order from Tayda, for example, they're only a few cents each.

[11-90-an]

Any chance there's something that I can do to mod a big muff to make the output even louder?  Even before the pedal broke down this is something I had wished for.  Big Muff's just don't have high enough output to slam into an amplifier like say a Fuzz Face does. 

Maybe putting a LPB-1 booster before or after? 

[CozmikKing]

Actually now that I've been playing it for a bit I realize that the overall output volume is much greater than it had been previous to needing to fix it.  That cap must have been bad for a long time.