tubescreamer troubleshooting

[ward]

I have a tube screamer that is giving me a hard time.
This is the schematic I followed:
http://www.tonepad.com/getFile.asp?id=81

Strange things is, in test mode it always works,
this is with a signal generator for input and into a fostex active monitor.
When I come home and plug in a guitar and a guitaramp, no sound.
When I roll back the volume on the guitar it suddenly passes sound ???

Q1 is the suspect stage,
in effect mode the bias is correct:  C=9V    B=3,5V    E=3V
when in bypass mode the base drops to 0,2V, emitter to 0V
Only difference in bypass mode is that the input goes to ground, and a signaling led is disconnected from ground.

I highly suspect the 0,027uF input capacitor, 
but cannot explain for myself why the circuit behaves like it does ??
Can someone enlighten me a bit?

Thanks!

 

[abbey road d enfer]

Looks like the input cap is shorted - or maybe you put a 27kohm resistor in place of a cap? When you put the unit in bypass, the base gets shorted to ground, which is coherent with your measurements. When you use a generator, its output impedance is low, so it manages to frive the transistor more or less well. with a guitar, the impedance is high, unless you roll down the volume pot, so at some time, there may be some sound going through.

 

[gemini86]

I believe this was meant for the lab.