Tube Screamer - Doesn't Work - Debug Help Requested

[angelkiller]

Hello,

I built a Tube Screamer based on the Tonepad PCB. I'm getting no output except for some occastional buzz or pop.

Here is the Tonepad page: http://www.tonepad.com/project.asp?id=1

I used the PCB from Tonepad. The only part substitution is a 50pf cap instead of 51pf. I don't know if it's a positive or negative ground circuit. The circuit does nothing except for buzz a little.

IC1 voltages
1 6.36v
2 6.35
3 4.73
4 0.01
5 6.20
6 6.41
7 6.38
8 7.84 (vbat)

Transistor voltages from left to right (as looking at the schematic)
1 0.0
2 0.0
3 7.78

4 7.78
5 3.03
6 3.34


Here's what I've debugged so far.

There was a resistor that was supposed to be grounded that wasn't... even though it was connected to a ground trace. So I manually added a wire from ground to this resistor. Resistances were then what I would expect in that area.

The IC voltages look high. It's grounded correctly and getting a power through pin 8. I don't know what high voltages on the other pins mean. I was expecting like 4 ish volts.

One transistor has no volts on two of it's pins. That sounds like an issue. I've resoldered it with no avail.

Can anyone point me in the right direction? Or walk me through step by step what I should do next. I've seen the debugging tutorial but it looks completely over my head.

Thank you.

[rousejeremy]

It's a negative ground circuit. Do you have an audio probe?

[R.G.]

IC1 voltages
1 6.36v
2 6.35
3 4.73
4 0.01
5 6.20
6 6.41
7 6.38
8 7.84 (vbat)

Did you also measure the DC voltage at the battery? If the voltage *right at the battery* is not larger than that, you are using a very old battery. If it is substantially larger, then there is a problem getting voltage to the circuit in the wiring.

And you're right, the voltages on pins 1,2,3,5,6, and 7 are too high. Leave the black lead of  your meter clipped to signal ground, then measure the voltage on the + pin of the 47uF in the lower left hand corner of the PCB population diagram as shown in the link. Report that voltage back here. It will tell me if what I think the problem is is actually there.

Transistor voltages from left to right (as looking at the schematic)
1 0.0
2 0.0
3 7.78
...
One transistor has no volts on two of it's pins. That sounds like an issue. I've resoldered it with no avail.

You're correct, this is not right. But I believe the transistor itself is not the problem. Measure and report back.

There was a resistor that was supposed to be grounded that wasn't... even though it was connected to a ground trace. So I manually added a wire from ground to this resistor. Resistances were then what I would expect in that area.

Is this a commercial board, or did you etch your own?

[angelkiller]

I remeasured the voltages with a newer battery. I'll admit I don't throw these things out until they hit 5v.

Vbat 8.60

1 6.41
2 6.42
3 4.86
4 0.01
5 6.27
6 6.45
7 6.47
8 8.02

Transistor voltages from left to right as in the schematic (not transistor pins)

1 0.00
2. 0.00
3 7.94

4 7.93
5 2.83
6 3.32

And the 47uf cap measured 4.5ish volts then slowly dropped to zero... I 'm guessing that this is normal capacitor behavior? I measured the 510k resistor that's connected to that pink trace and it measured a steady 4.64v

And I didn't etch this myself, I bought the PCB.

[Govmnt_Lacky]

Two things you can do easily...

1) Check ALL of your component values to ensure they are correct. Look at resistor color bands 2 or 3 times. (Are you SURE that is a 10K and not a 10 ohm or 100K?)

2) Check the entire trace side of the PCB for potential solder bridges and/or broken traces.

After that, build yourself an audio probe (search function) and follow the "Debugging: What to do when it doesn't work" thread.

Good Luck 

[R.G.]

That helps.
Your bias voltage is hosed up somehow, which is one of the things I was thinking might be a problem.

With the 47uF cap starting at half-battery (which is where it should stay all the time) and declining to zero, something is able to pull it down faster than the two 10K's can fill it.

(1) Are those really 10K's?
(2) What kind of meter are you using? Maybe the meter has a low input impedance. Some do.

For the next step, we need to find out why the transistor base and emitter are at 0V. Set your meter to read ohms, remove power from the circuit, and measure resistance from each transistor base to ground. What are those numbers?

And the 47uf cap measured 4.5ish volts then slowly dropped to zero... I 'm guessing that this is normal capacitor behavior? I measured the 510k resistor that's connected to that pink trace and it measured a steady 4.64v

Which end of the 510K resistor stayed steady? And which 510K resistor? There are two.

[angelkiller]

That helps.
Your bias voltage is hosed up somehow, which is one of the things I was thinking might be a problem.

With the 47uF cap starting at half-battery (which is where it should stay all the time) and declining to zero, something is able to pull it down faster than the two 10K's can fill it.

(1) Are those really 10K's?
(2) What kind of meter are you using? Maybe the meter has a low input impedance. Some do.

For the next step, we need to find out why the transistor base and emitter are at 0V. Set your meter to read ohms, remove power from the circuit, and measure resistance from each transistor base to ground. What are those numbers?

And the 47uf cap measured 4.5ish volts then slowly dropped to zero... I 'm guessing that this is normal capacitor behavior? I measured the 510k resistor that's connected to that pink trace and it measured a steady 4.64v

Which end of the 510K resistor stayed steady? And which 510K resistor? There are two.

First, I made a modification to the circuit trying to fix something. I have reversed this modification and the circuit is (to the best of my ability) exactly like the schematic.

That said, the 47uf cap starts at .30v and works its way down. There is also 0 volts on the two left-most pins of the left-most transistor. (Q1) So it appears I still have the same problems.

To answer your questions,

Yes they are all 10k resistors. Brown-black-black-red-brown. Same as the other 10k resistors in the circuit.

I'm using a $20 Radio Shack multimeter. Not the best I know. But it appears up the the task. But what would I know. (seriously)

The base of Q1 to ground is 199 kilohms. Not sure what it's supposed to be and that's not a typo. Meter set to 2M and it says .199.

The base of Q2 to ground could not be determined. I just got no connection. I suppose that's bad no? Could be my solder work. I can get resistances on the Collecter (7 kohms) and I can get a resistance on the Emitter (9.96 kohms) but nothing on the base.

The answer to the other questions tomorrow sometime. (Sorry)

[angelkiller]

This is what I'll leave you with.

Vbat 7.79

IC1
1 7.61
2 7.61
3 7.63
4 7.79
5 7.79
6 7.58
7 7.59
8 7.64

Q1
B .59v
C 7.80
E 7.57

Q2
B 5.14
C 7.80
E 7.58

Resistors in the bottom right corner, starting at the 510k working towards the last 10k. Measuring voltage at the 'bottom' of the resistor as oriented in the schematic.
510k - 7.64v
10k - 7.65
510k - 7.74 (? shouldn't it be the same as the previous 2 resistors as it's on the same trace?)
10k - 7.74 (This is supposed to be ground...)
Ra (100) - 7.59
10k - 7.67


Nothing's consistant. My soldering iron/skills suck and I'm considering scrapping this one it seems over my head.   

[angelkiller]

Two things you can do easily...

1) Check ALL of your component values to ensure they are correct. Look at resistor color bands 2 or 3 times. (Are you SURE that is a 10K and not a 10 ohm or 100K?)

2) Check the entire trace side of the PCB for potential solder bridges and/or broken traces.

After that, build yourself an audio probe (search function) and follow the "Debugging: What to do when it doesn't work" thread.

Good Luck 

I checked as many as I could. I don't really have extra parts so unless I mis-ordered, I should have the right parts. I know that's an assumption.

My soldering skills/iron suck but I did my best to keep everything bridge-free and connected.

It's a negative ground circuit. Do you have an audio probe?

I did build an audio probe. Audio makes it to the Q1 transistor and stops. Follow the audio input line. I get audio on the 1k resistor, but not at the base of Q1.

[R.G.]

This is what I'll leave you with.
...
Nothing's consistant. My soldering iron/skills suck and I'm considering scrapping this one it seems over my head.   

That was what I needed. You have an open ground wire to the circuit. It's not getting any power to run. That is at least one problem in it. There may be others once you get that fixed.

To fix this one, you need to use your meter as an ohmmeter to find the break (that is, resistance greater than zero ohms) between the battery negative and the circuit. It is possible that your circuit is wired so that unless you have a plug in the input or output jack, ground is not connected. If so, you need to stick a jack into the socket(s) to see if that gets power to the circuit.

[angelkiller]

That was what I needed. You have an open ground wire to the circuit. It's not getting any power to run. That is at least one problem in it. There may be others once you get that fixed.

To fix this one, you need to use your meter as an ohmmeter to find the break (that is, resistance greater than zero ohms) between the battery negative and the circuit. It is possible that your circuit is wired so that unless you have a plug in the input or output jack, ground is not connected. If so, you need to stick a jack into the socket(s) to see if that gets power to the circuit.

One step at a time I suppose. You were right. The solder pad for the ground pin had come off (messy soldering) So I think only half the circuit had a ground. Now the voltages are working how I'd expect.

The IC pins have voltages from like 3.5ish to 5ish volts. The grounds are grounded. The positive terminal of the 47 uf cap is a steady 3.87v (the whole pink trace is at 3.87v).

Now the only problem I see is on Q1. The collecter has voltage. The base and emitter do not.

I have cords plugged into the input and output of the circuit.

I also noticed that the bottom most 1uF cap (the one connected to the emitter of Q1) has 3.87 volts on the left side. Is that good, bad or irrelevant?

And thanks for all the help everyone has given me.

[Govmnt_Lacky]

Check for a solder bridge between the Base and/or Emitter of Q1 and the nearby Ground trace (right by the 220 ohm resistor)

[angelkiller]

Check for a solder bridge between the Base and/or Emitter of Q1 and the nearby Ground trace (right by the 220 ohm resistor)

Checked and double checked. It's good.

The two transistors never made great contact with the PCB. I got tired of them coming loose, so I fashioned some IC sockets for them. Now:

IC1:
B - 0.60v
C - 6.95v
E - 0.12v (?)

IC2:
B - 0.76v
C - 0.28v
E - 6.88v

edit: Audio probe works on the base of Q1!

[R.G.]

The two transistors never made great contact with the PCB. I got tired of them coming loose, so I fashioned some IC sockets for them. Now:

This is not a criticism, just an observation. If the transistors never made great contact with the PCB, the solder joints on the entire PCB are suspect. Putting in sockets only helps if the solder joints to the new socket contacts are soldered in properly.

IC1:
B - 0.60v
C - 6.95v
E - 0.12v (?)

IC2:
B - 0.76v
C - 0.28v
E - 6.88v

It is quite difficult to tell what is going on, as the new (and presumably different) voltages for the battery and power supply voltages on the PCB are not included. It looks very much like the battery has sagged to something like 7V. If so, it's worn out, and will vary during readings.

There is still something very wrong with the power to/from the two transistors (and I'm guessing here that you meant transistor 1 and 2, not IC1 and 2, right?)

Can you give us the full set of voltages again?

I think from the voltages that you may have mixed up the labels of E, C, and B on the transistors as well. Both collectors should be at the same voltage, which is ?about? 7V. Unless the path from the bias voltage is open or very high resistance, the bases should be more than a fraction of a volt, unless the emitters are nearly shorted.

So there are still mysteries about what is connected to what. Things that are connected by traces will have identical voltages.

[Govmnt_Lacky]

Do yourself a favor and get a brand new 9V battery 

+1 to RGs recommendation for a fresh set of debug voltages 

[angelkiller]

It is quite difficult to tell what is going on, as the new (and presumably different) voltages for the battery and power supply voltages on the PCB are not included. It looks very much like the battery has sagged to something like 7V. If so, it's worn out, and will vary during readings.

There is still something very wrong with the power to/from the two transistors (and I'm guessing here that you meant transistor 1 and 2, not IC1 and 2, right?)

Can you give us the full set of voltages again?

I think from the voltages that you may have mixed up the labels of E, C, and B on the transistors as well. Both collectors should be at the same voltage, which is ?about? 7V. Unless the path from the bias voltage is open or very high resistance, the bases should be more than a fraction of a volt, unless the emitters are nearly shorted.

So there are still mysteries about what is connected to what. Things that are connected by traces will have identical voltages.

Mistakes, mistakes everywhere! I try my best though. 

Vbat 9.70v
Vbat connected in the circuit 8.17v (?)

IC1:
1 5.48v
2 0.89v
3 4.38v
4 0.00v
5 5.35
6 5.50
7 5.50
8 8.01

Transistor pins from left to right as per the schematic. (Since I misuse the actual terms.)
1 0.20v
2 0.08v
3 7.99v
4 7.98v
5 0.87v
6 0.40v

Something interesting  I noted was that my batteries are dying very very quickly. By the time I finished measuring my voltages, Vbat connected to the circuit (was 8.17v) is now 7.93v.

[angelkiller]

One month bump! Still can't get this working. And I haven't the faintest idea what could be wrong.

vBat: 7.31v

IC1:
1 4.40
2 3.79
3 3.80
4 0.00
5 4.30
6 4.40
7 4.40
8 7.28

Transistors pins from left to right as per the schematic. (linky)

1 0.73
2 0.59
3 7.09

4 7.08
5 2.42
6 2.82

I have an audio probe. Audio makes it to ic pin 3 and that's as far as I can find it.

Any help or advice or whatever is appreciated. Thanks. 

[aron]

Do you get any sound on pin 1?

[pakrat]

I just completed a tonepad tube screamer that works properly. I can post my voltages if anyone thinks it would help.

[R O Tiree]

See if you can upload high-definition, well-focused pictures of both sides of the board. Keen eyes might be able to spot either misplaced components or potential problems with solder joints.