Need help debugging my ts808

[fryguy]

For reference, this is my first build and my first time debugging.

1.What does it do, not do, and sound like? Effect off: Regular bypass tone. Effect on: You can hear the OD, but there is a terribly loud popping / crackling over the top of it.
2.Name of the circuit = El Griton (Tubescreamer from tonepad)
3.Source of the circuit (URL of schematic or project) = http://www.tonepad.com/project.asp?id=1
4.Any modifications to the circuit: Nope
5.Any parts substitutions: Switched the 51pF cap for a 47pF cap
6.Positive ground to negative ground conversion: No?
7.What is the out of circuit battery voltage? => 9.26V

Q1
C =9.2
B =7.9
E =7.3

Q2
C=9.2
B=4.0
E=3.2

IC1
P1:3.83
P2:3.83
P3:3.72
P4:0.00
P5:3.70
P6:3.70
P7:3.65
P8:9.17

D1
A  =3.38
K  =3.6

D2
A =3.55
K =3.38

D3
A =3.55
K = 3.55

The IC and the transistors are not in sockets because I didn't know to use them whenever I was putting the board together. The readings on Q1 seem a bit funky. Perhaps it is fried? I have no idea. Any help is appareciated and I can provide pictures or sound clips or whatever is needed.

Thanks,
Michael

[R.G.]

You identified the problem correctly yourself - Q1 is not working correctly.

The base being at 7.9V and the emitter at 7.3 says the base is being pulled up too high. Look for soldering shorts along the path from the base back to the bias voltage source.

It is also possible that the emitter is open, or the emitter resistor does not make contact with ground, but there is still the base problem.

[fryguy]

You identified the problem correctly yourself - Q1 is not working correctly.

The base being at 7.9V and the emitter at 7.3 says the base is being pulled up too high. Look for soldering shorts along the path from the base back to the bias voltage source.

It is also possible that the emitter is open, or the emitter resistor does not make contact with ground, but there is still the base problem.

I don't quite understand what you mean (showing my ignorance here), but I checked for shorts and bad joints and didn't find any. Does this mean the transistor is possibly fried? If so then I could just run to radioshack and pick up another and swap it out. I guess it couldn't hurt to do that either way.

[petemoore]

You identified the problem correctly yourself - Q1 is not working correctly.

The base being at 7.9V and the emitter at 7.3 says the base is being pulled up too high. Look for soldering shorts along the path from the base back to the bias voltage source.

It is also possible that the emitter is open, or the emitter resistor does not make contact with ground, but there is still the base problem.
  This would be my guess.
  Measure each resistor [compare measured value to schematic value] and all the bias connections around the transistor. There could be a connection which needs to be eliminated also, check for stray connections.

[fryguy]

Good news! I ended up running to radioshack to pick up a 2N3904 transistor to swap it out just incase it was fried, and it worked! Now would be the time to stuff everything into an enclosure if I had finished adding my decal and clearcoating it but I got caught up with the debugging. 

As far as the tone goes: I play a VOX AC15CC1 and I think the pedal's overdrive with the gain maxed out sounds nearly identical to the crunch I get from my amp with the top boost cranked and the master volume around noonish, which is great, because now I can get that crunch without having to wake up the neighbors. 

[fryguy]

Okay, something seriously funky is going on here. I was playing with the pedal on, and without touching or accidentally moving the pedal or anything, the crackling and popping noise started again. Slightly bewildered, I hit the standby switch on my amp, grabbed my voltmeter, and checked the voltage across the trasistors. They read normal so I flicked off the standby switch and the crackle was gone.

That was a few hours ago and I figured either I was crazy or it was just some freak occurance, but no, it happened again! I was just noodling around a bit and after a few minutes the crackle and pop came back. I checked the voltages on the transistors and on Q1 the base and emitter were both reading close to 8 volts again. Frustrated, I went and grabbed a drink and when I came back they tested fine and the pedal isn't making noise anymore.

What on earth is going on? 

[Sir_Ian]

Okay, something seriously funky is going on here. I was playing with the pedal on, and without touching or accidentally moving the pedal or anything, the crackling and popping noise started again. Slightly bewildered, I hit the standby switch on my amp, grabbed my voltmeter, and checked the voltage across the trasistors. They read normal so I flicked off the standby switch and the crackle was gone.

That was a few hours ago and I figured either I was crazy or it was just some freak occurance, but no, it happened again! I was just noodling around a bit and after a few minutes the crackle and pop came back. I checked the voltages on the transistors and on Q1 the base and emitter were both reading close to 8 volts again. Frustrated, I went and grabbed a drink and when I came back they tested fine and the pedal isn't making noise anymore.

What on earth is going on? 

Do you have your pedal in an enclosure? Because when I don't, i always get tons of crackly. If it is, I wonder how your board is secured to it. Is it screwed in on stand-offs or is it just floating around? if its just floating around, that might be your problem. If your circuit it bumping up against your enclosure it would be grounding out, or something of that sort. Another possibility is a wire bumping up against something. Basically, what I'm trying to say is it sounds like you have a connection that is temporarily being made that shouldn't be, or you might have a cold solder joint which is temporarily losing a connection which should be made. Or maybe its sun spots....... <_<      >_>

[ayayay!]

Can you plug it into another amp?  Your transistor was definitely no good it seems, but there may have been more than one problem.

Troubleshooting is always about isolating and proving what IS good.   

[fryguy]

Do you have your pedal in an enclosure? Because when I don't, i always get tons of crackly. If it is, I wonder how your board is secured to it. Is it screwed in on stand-offs or is it just floating around? if its just floating around, that might be your problem. If your circuit it bumping up against your enclosure it would be grounding out, or something of that sort. Another possibility is a wire bumping up against something. Basically, what I'm trying to say is it sounds like you have a connection that is temporarily being made that shouldn't be, or you might have a cold solder joint which is temporarily losing a connection which should be made. Or maybe its sun spots....... <_<      >_>

It's not in an enclosure. I have it spread out on top of a static free bag one of my old video cards came in. To compensate for the lack of enclosure I've also got an extra wire running from the output jack shield to the input jack shield. I'll be clearcoating my enclosure today and drilling the holes a day or two later. I ordered some standoffs from smallbear and everything so I should be okay getting everything in there correctly.

I can take it over to my friends and try it out on his amp in a few days after I get it in the enclosure. I don't think it's the amp, though. I can turn the pedal on and it sound good for about 5 minutes before it starts being noisy again, and then if I just turn it off and leave it alone for another 5 it goes back to working. Maybe it's the voodoo. 

[MikeH]

It's possible that you have an incorrect component installed or a solder bridge someplace that is somehow making things funny after a certain amount of time/power/whatever.  I say double check your parts layout and check for continuity between traces.  I've found the most invaluable tool in debugging is the continuity tester on my DMM; I find 80% of problems that way.

[kurtlives]

It's possible that you have an incorrect component installed or a solder bridge someplace that is somehow making things funny after a certain amount of time/power/whatever.  I say double check your parts layout and check for continuity between traces.  I've found the most invaluable tool in debugging is the continuity tester on my DMM; I find 80% of problems that way.

Yes +1. I often think something is grounded then test for contuinuity and find its not.

[fryguy]

I've found the most invaluable tool in debugging is the continuity tester on my DMM; I find 80% of problems that way.

This may sound ridiculous, but how exactly do I go about testing everything for continuity? I believe I just touch one lead to the ground (output jack shield) and then touch the other to various points in the circuit where the schematic says it should be grounded. Is that correct?

Sorry for the silly question. 

[fryguy]

Well, I had nothing to do tonight so I drilled the holes and mounted everything into the enclosure. Had a bit of trouble fitting everything in there (I am retarded and made all my wires like 6" long) but whatever. Live and learn!

My tone pot seems to have died, which is frustrating. I checked the resistance with my DMM across the first and third lugs and it reads 0, so I am pretty sure it's dead, but whatever. I can live with that for now and just order another next time I place an order at smallbear. Thanks for all the help everyone!

Edit : Oh yeah. Forgot to mention that outside of the tone pot it completely works now. Heh. Guess I was excited.

[MikeH]

To check continuity set your DMM to the little diode symbol (-->|).  Now when you touch the 2 leads together it should make a beep, or a bell should ring, or a cucku bird should pop out or something.  Now you can use the 2 leads to probe your board.  Things to check:  1) Make sure there is no continuity between adjacent traces.  Sometimes microscopic threads of solder can cause connections between traces that can't be seen with the naked eye (this is where I mention that a magnifying glass i also a very helpful tool,  2) Make sure that all ground points are connected.  It's possible (it's happened to me) that you ground trace becomes interupted (although it looks fine) and half your circuit is not grounded.  So you should check all ground points against the input jack or your star ground. 3) Check continuity of switches.  Make sure they are opening and closing properly 4) check for shorts in your power supply 5).... etc, etc, etc 

Basically make sure that everything that should be connected is, and everything that shouldn't be isn't.