My newly built BSIAB2 broke..

[Mihkel]

Hello,

So recently I built the BSIAB2. I got it working nicely, even in a box, but I decided to shorten the wires a bit. I made them as short as I could (while leaving some slack)  and tried it out. I got only *very* weak sound. I spent the whole last night thinking what could be wrong. So today when I came home, I built myself an audio probe and found out that the signal stopped at the volume pot. I must have overheated it while desoldering the wires ( it's a plastic pot). I checked the pot with a DMM and indeed it was broken. So I wired the Out effect wire straight to the output jack and tried it out. "Woo, success!" I thought, but I soon understood that it isn't the BSIAB it used to be. The sound was bad; had no sustain and was unbiased. I thought it would be fixed with a simple tweaking of the bias pot. This is where we get to the actual problem. I can't get it biased properly! The bias pot doesn't do a whole lot.
So here's the info:
1. What does it do, not do, and sound like?
It works, distorts, but it sounds unbiased and i can't get it to bias.
2. Name of the circuit = BSIAB2
3. Source of the circuit = http://66.226.81.4/diagrams/bsiab_2_sc.gif
4. Any modifications to the circuit?
No
5. Any parts substitutions?
All fets are 2N5457
6. Positive ground to negative ground conversion?
No
7. Battery voltage 9.4V
  Voltage at the circuit board end of the red battery lead = ~9.06V
  Voltage at the circuit board end of the black battery lead = 0.00V
Q1:
D=4.01V
S=0.64V
G=0.00V
Q2:
D=7.92V
S=3.66V
G=0.01V ( :? )
Q3:
D=3.81V
S=0.00V
G=0.00V
Q4:
D=7.89V
S=3.20V
G=0.01V
Q5:
D=0.44V
S=0.43V
G=0.00V

So there's definately something wrong compared to GGG readings. But I just don't know what and how, since I didnt make any modifications to the circuit board itself ( It's Torchy's vero layout btw ).

Thanks to everyone who even bothered to read this through.  :wink:

[petemoore]

I'd look around Q3 and Q5, they aren't biased...
 If you socketted the transistors [or maybe even if not] you might get some accurate readings of in circuit resistors [but another,. alternate path through the circuit for the reading may show lower value than the resistors color code...].

[petemoore]

Jfet bias info from GEO, the source has to be higher V than the gate, [.7v IIRC] and the drains for gain stages about 1/2v or so of V+....4.5v.

[Mihkel]

Thanks for the replies, Pete

Everything looks in order though. It seems to me that for a few seconds after plugging in the effect, it works normally, and then starts acting up. Again, this is only how it seems. I'm getting pretty close to building it again, but that's something I would rather not do. I'm afraid of burning the fets (and possibly other components) and the sockets I have don't seem to offer the best connection.  

Any other ideas before I start desoldering the components?

Thanks

[Mihkel]

Well, it seems like i have found the culprit
It's the Drive pot also, that has gone crazy by soldering. I twiddled with the lugs and got normal sound out of it. I didn't find the right bias yet, but thats because I had to move the pot lugs all the time to make it work ( I hope). I'll try to get a new pot ASAP.

Thanks for your time!