Help with Tonepad DS-1 Debugging

[jukeboxhero01]

Hello,

I'm having trouble with the Boss DS-1 from Tonepad. I am not getting any guitar sound out of the circuit. I've used my DMM to check for shorts. I found a few shorts, then fixed them. I've made the 3 bare wire connections on the board. I'm using the TL072 parts list. The IC is the OPA2134PA.

The IC pinouts are as follows:
pin 1 = 4.75V
pin 2 = 4.75V
pin 3 = 4.68V
pin 4 = 0V
pin 5 = 4.75V
pin 6 = 4.75V
pin 7 = 4.75V
pin 8 = 9.48V

The Transistor pinouts are as follows:

Q1
C = 9.48
B = 4.17
E = 3.76

Q2
C= 0.89
B= 0.63
E= 0.02

Q3
C= 9.48
B= 3.68
E= 3.39


Schematic:
http://www.tonepad.com/getFileInfo.asp?id=78

[jkokura]

IC, Q1, and Q3 look fine. Q3 looks suspect to me, but I don't know if that what it's supposed to be. Try double checking your Q2 orientation, and then make sure it's all connected properly, that the parts around it are installed properly and soldered properly.

Double check the wiring and if you've found some shorts perhaps there are more. Who made the board? Is it the Tonepad board or is it a home etch? Are you sure of the orientation of your parts? Have you got access to an Audio Probe?

Jacob

[Earthscum]

Aye, Q2 looks suspect. The collector of Q2 should be around 4-6V, or somewhere close to halfway between V+ and ground. The base should be somewhere right above that. I'm willing to bet you misread a resistor? I had a bout where I kept trying to use 2.2k's instead of 22k's, and really struggle sometimes with 22 vs 27 (re-red vs red-violet). Or maybe a bad solder joint? Or the transistor is bad if all else checks out, or backwards? I'd start on that transistor though... everything else looks pretty good at a glance.

[jukeboxhero01]

I don't have an audio probe. It's a home etch, but previous boards that I've made have worked. I have no idea what the problem is, but I'm guessing that it might indeed be a bad board. While I was replacing components on the board, two traces actually broke. I did repair them and still attempted to troubleshoot. I've checked the resistors surrounding Q2, and replaced the transistor itself. I still have the same problem. I tried connecting Q2 one pin at a time and reading the voltages. When I connect the collector pin, it's receiving around 9V, when I connect the base pin, it's receiving around 8V, but when I connect the emitter pin, all the voltages on the pins drop to less than 1V.

[jkokura]

Well, at least you know where the problem is! First step to fixing it I say.

I find that generally, when there's a problem at a transistor, it's pretty easy to look around it and find a solution. It could be any direction from it, but look very carefully and you will find it!

Double check you parts values, orientation, soldering job, and of course triple check them if you can't see anything. Take some time away, or if, like you thought, it's a bad board - make another and start over.

Jacob

[petemoore]

  Distant point testing.
  For Q2 C Resistor, there should be 10k, starting at the transistor lead, and through as many solderjoints and wires [sometimes the V+ is at the battery clip so it can get checked too] as possible, then any others that go to that pin.
  a small test clip makes it easier to hook to the pin.
  Mostly using DMM [diode checker [beeps when probes touch] to verify connections, the appropriate R range settings, voltage] in every possible fashion and especially that help make sense of it.