SOLVED Need help checking voltages with a Sandspur.

[ryugu]

All I'm getting is a faint sputtering, and only with the fuzz knob turned all the way up. I tried several different positions with trim pots and got the same results. My only guess is that I overheated the transistors because I didn't use sockets. I was otherwise very careful building this. Where can I start with voltage checks?

 

[andare]

DMM black probe to ground (enclosure hole) and red probe to the collectors. Q2c should be around 1.2V, Q2c around 5V.

 

[ryugu]

Thank you. I got 1.1v and 7.4v. Does this tell us anything?

 

[Funnel]

The bias trim should adjust the voltage for q2. Are you able to set it to 4.5-5.0v. Have you done a reflow on the solder joints and cleaned the pcb?

 

[Big Monk]

What’s going on here?;



In my experience, many problems like this are caused by bad joints, especially near the emitter of Q2 on the Fuzz Face.

Check this joint but in general check ALL your joints.

 

[Mcknib]

Q1 base looks like it lacks solder

As said re bias Q2 collector to around 4.5v ish set the sundial so you get 9v on lug 1 (fully CCW) then use the bias trimmer to set Q2 collector to 4.5v

*Edit I should say set the sundial to 9v ish that depends on what your power supply puts out and the little bit of voltage drop through D1 not all 9v adaptors put out exactly 9v especially unregulated one's

 

[ryugu]

What’s going on here?;


In my experience, many problems like this are caused by bad joints, especially near the emitter of Q2 on the Fuzz Face.

Check this joint but in general check ALL your joints.

Yup, good eye. I accidentally soldered the left and right pots backwards, and had trouble with that one lug when I resoldered.

I think it's soldered thoroughly, but maybe I damaged the pots with too much heat or something???

 

[ryugu]

SOLVED

I took the whole thing apart, followed everybody's advice, put it back together and sounding f'n great!

Thanks for the help everybody. This is a fantastic community.

 

[MichaelW]

@ryugu

Another PedalPCB forum "Troubleshooting Guru's" FTW!
I love this fuzz! Did you use BC108C's? I've read of some folks using BC183's for a slightly warmer sounding fuzz. I socketed my transistors and might give that a try.

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