Tube Screamer problem

[Skullnick]

Hello,
After building a tube screamer from the tonepad layout and loving it I decided to make another one. The problem with the second one is that when I plug it in I get only the clean signal and gain and tone controls don't seem to work. Can anybody please help me in solving the problem?
Thanks.

[petemoore]

The problem with the second one is that when I plug it in I get only the clean signal and gain and tone controls don't seem to work.
  This is a solid indication it needs debugged.
Can anybody please help me in solving the problem?
  Yes, however we need your help too, see the sticky "Debugging...what to do when it doesn't work", after doing one or two, applying debugging chops finds the general location of the problem, a bit more digging generally finds the solution pretty quick.

[Skullnick]

Really sorry about that. So silly of me not to give the measurement.
After a bit of debugging my signal is clipped and fades away quickly. Everything in the project is by the TS808 specs except for the diodes which are 1N4148 instead of 1N914 and the 0.22uF tantalum caps are replaced with ceramic ones.
Here's the link to the schematic and layout I used:
http://www.tonepad.com/getFile.asp?id=81

Here are the reading I've gotten:
IC:
P1: 10.89V
P2: 9.26V
P3: 9.27V
P4: 0
P5:1.92V
P6:1.93V
P7:1.93V
P8:12.75V

Q1:
C:12.64V
B:3.36V
E:3.96

Q2:
C:12.64V
B:3.38V
E:4.02V

D1:
A:9.08V
K19.17V

D2:
A:19.19V
K:9.67V

D3:
A:9.74V
K:9.14V

[anchovie]

Something is very wrong with your bias voltage (the points marked Vb on the schematic) - it should be half the supply voltage (which judging by your voltages for pin 8 of the IC and the transistor collectors is coming from an unregulated power supply, hence way higher than 9 volts because the PSU isn't under full load).

[Skullnick]

Something is very wrong with your bias voltage (the points marked Vb on the schematic) - it should be half the supply voltage (which judging by your voltages for pin 8 of the IC and the transistor collectors is coming from an unregulated power supply, hence way higher than 9 volts because the PSU isn't under full load).

I've used the power supply with 3 or 4 pedals before and there were no issues.

[petemoore]

  So you have 12 some volts DC, correct polarity.
  But the opamp pins should be around 1/2v [except the ground-pin4, and the V+, pin8].
  I would check the voltage and resistor values at the voltage divider. The two resistors [from V+ and Gnd.] should be equal value, and hence divide the voltage in 1/2.

[Skullnick]

  So you have 12 some volts DC, correct polarity.
  But the opamp pins should be around 1/2v [except the ground-pin4, and the V+, pin8].
  I would check the voltage and resistor values at the voltage divider. The two resistors [from V+ and Gnd.] should be equal value, and hence divide the voltage in 1/2.

I've checked all the component values and they seem to be ok.

[anchovie]

Test the voltage divider as a subcircuit rather than just checking the individual components. Measure the resistance from the V+ on your power socket to the middle of the divider and likewise from the middle of the divider to power socket ground.

[Skullnick]

I compared the measurements in the voltage divider with the working tube screamer and they seem to match (around 6V) but the measurements on the IC are way off.

[anchovie]

If you look on the parts layout diagram in the Tonepad PDF you'll see the Vb trace is the red one. All I can suggest is inspecting that trace on your board and making sure there are no unwanted shorts or breaks in it.

[petemoore]

Here are the reading I've gotten:
IC:
P1: 10.89V  An output pin, can't swing far toward +12.75 from this bias.
P2: 9.26V This opamp stage has all it's pins [- & + inputs, output] leaning toward V+.
P3: 9.27V  Something is too low Resistance to V+, or something isn't pulling toward Gnd. enough [too high R]...elevated or floating for some reason.
P4: 0v = Gnd.
P5:1.92V 
P6:1.93V
P7:1.93V This OA2 opamp stage is biased near ground, signal swing toward - has nowhere but ground, immediately because the opamp needs a little elbow room, it is symmetrical/opposite in it's offbias'dness compared to OA1,
something is pulling toward ground kind of hard or there's a super high or floating resistance to V+.
  P8:12.75V...the capacitors Are rated for >16v ?
Q1:
C:12.64V
B:3.36V
E:3.96
  These are bipolar transistors? the base might come up to suitable bias when the opamp voltages are sorted out, base one diode drop above emitter.
C:12.64V
B:3.38V
E:4.02V
   Start running the 'dogmatic' checks, test for cross-continuities [make sure what is supposed to be open is open], measure every resistor from 'distant point'..allows simultaneous resistance and continuity testing.