Tonepad TS 808 debugging help

[jkokura]

2nd of 3 - My Small Stone and Ross Compressor are also not working, but you can see the other posts for the progress being made on those.

1.What does it do, not do, and sound like?

Currently, it bypasses a good clean sound, and when activated the LED lights up but does not give me any sound.

2.Name of the circuit =

Tube Screamer

3.Source of the circuit (URL of schematic or project) =

http://www.tonepad.com/getFile.asp?id=81

4.Any modifications to the circuit? Y or N

Nope, built to TS 808 specs with symmetrical clipping (jumper in place of D3)

5.Any parts substitutions? If yes, list them.

nope

6.Positive ground to negative ground conversion? Y or N

Still not sure about what this means.

7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => 8.85

Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead = 8.83
Voltage at the circuit board end of the black battery lead = 0

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

Q1
C = 8.81
B = 3.3
E = 2.76

Q2
C= 8.81
B= 3.3
E= 2.76

IC1
P1 4.38
P2 4.45
P3 4.38
P4 0
P5 4.37
P6 4.37
P7 4.38
P8 8.81

D1
A (anode, the non-band end) = 4.45
K (cathode, the banded end) = 4.37

D2
A = 4.37
K = 4.45

[Electron Tornado]

Use an audio probe to check the signal path to find where you have a good signal and where the signal is lost.  If all the components have been installed correctly you may have a bad solder joint somewhere.

A couple of other simple things that have tripped up more than one person:
1. input and output cords connected backwards
2. volume control on pedal set to minimum

[jkokura]

Thanks for the post.

I wish I had an audio probe at this point. I'm going to look again at how to build one and may have one running later today.

As to the other issues, I guess what I'm wondering is if anyone sees any problems with either the numbers above, cause if not there's a problem with my wiring and I can do that again easily. To me, the numbers on the IC, Trannies and the Diodes look normal, making me pretty sure my soldering's not the issue. I'm fairly certain it's going to be wiring, at least on this one... Anyone see something that proves that wrong?

Jacob

[petemoore]

http://www.geofex.com/

[jkokura]

Tried again last night, nothing yet.

Is it a problem with the numbers or a problem with my wiring...

[jkokura]

I got sound!

But it's crap.

I rewired it entirely, but now my LED isn't lighting up, and instead of a good powerful signal, I'm getting the sound but at a perceived db loss from clean signal. Knobs are all dimed, so it's not needing to be turned up.

I tried resoldering some PCB joints that looked slightly suspect, but nothing better yet.

At least I got sound. I'm going to re-examine all my wiring again. At least I know it 'can' work.

Jacob

[jkokura]

I just did something by accident and it made the led light up.

I touched the battery to the battery clip backwards (Postive to negative and negative to positive). It made the LED light up. Haven't seen what it sounds like, but I'm wondering if that could be the problem? I figure I've got the LED wired in backwards, but would that cause the circuit to not be working?

Jacob

[jkokura]

Alrighty. Flipped that LED around and the LED is working, but no improvement on the sound.

Just to clarify - after posting the above stuff, currently I get similar readings when probing as described in the 'debugging procedures.' Numbers seem to be right.

Now my wiring seems to be fine also, with sound passing in both bypass and when Engaged. LED lights up as expected to. However, when effect is engaged, a significant volume drop occurs. When all knobs are turned up full, sound still does not equal bypass signal. I always thought tube screamers were supposed to have the ability to boost the signal not drop it, so I'm figuring I've either got a part in the wrong spot or at the wrong value. Does anyone else have a suggestion? I'm poring over the PCB looking for possible mistakes, but if that's not the issue than let me know please!?!?!

Jacob

[nbabmf]

Check your jacks and switch to see if they're wired correctly.  Pay special attention to be sure nothing is touching something it shouldn't.  I always wired the jacks directly to the board first, with longer wire than I need, to make sure the circuit works, and then connect it to the switch.

[jkokura]

Now my wiring seems to be fine also, with sound passing in both bypass and when Engaged.

Thanks for the suggestion, but that's what I did for 3 hours last night. I'm fairly confident now that the wiring is correct. Sound is fine when bypassed, and I think that means the jacks are wired right. I've been over it, the wiring is done right, and all connectivity tests are positive. It's wired right.

I got a suggestion from someone else that the Tant caps are potentially the problem. Any thoughts on that? I thought the polarity didn't matter here, so is it possible that I've wired one in backwards? Fortunately I have some tant spares.

Using the Tonepad PCB - what way should the polarity of the tant caps go? (.22uF) http://www.tonepad.com/getFile.asp?id=81

Jacob

[ralley]

Polarity does matter with tantalum caps.  Typically they will be marked with a small "+" at the positive side.  In the layout you linked to the horizontally orientated tantalum has the negative side to the right (to ground via the 220 ohm resistor) the vertically orientated cap has the negative side to the bottom (straight to ground).
Rob.

[jkokura]

Thank you. I think that's the way they are now, but I'll double check tomorrow, and then also switch them out. worse comes to worse I just have different tant caps in there and an effect that isn't working right still. If that fails, I'll start double checking my solder joints again.

jacob

[jkokura]

Alrighty. I changed both the tant caps, and also changed the IC a third time. Nothing. I've cleaned all the Rosin off the PCB and made it nice and sparkly. I have rewired this thing multiple times, and it's blowing my mind trying to figure out how to make it work.

The can't think of doing anything else - can anyone else give me anidea of what I should do?

Jacob

[Brymus]

Try the ciruit on your breadboard if it works there you can make it work on a PCB too.
But really the audio probe would really help you since its all soldered up.

[bigchasbroon]

i built a ts9 and the sound was crap i checked everything and was convinced it was right. After trying everything i made an audio probe took me 2 minutes to realise that i had the wrong value cap at the input buffer. swapped it with the right value and taht was that. Audio probe is by far the most useful debugging tool to the diyer.

[jkokura]

I think that Cap is a 51pf cap right? I have 47pf Cap in there, or at least I thought I did. I think I have a spare 51pF, and if not I'll have to see if small bear has one.

*EDIT* Spoke too soon. The 51pF cap isn't on the input, and if it's 47pF I think it's fine. The input cap is the 0.027uF cap. Perhaps I'll look at that one and find the problem.

Thanks big

Jacob

[svstee]

There won't be any real difference between 47pf and 51 pf anyways.

One thing you might want to do is check the voltage on all polarity sensitive capacitors. That would let you know if you have a power polarity issue.

Also, since you have checked the wiring multiple times, you might want to go back and doublecheck all component values. It is dull and tedious work, but you might find your problem doing it that way. Hope this helps!

[petemoore]

  20% cap values won't make it not work, you'd probably have to go like 10x any of those values...anyway you can read and swap the uf's, if they're anywhere ballpark close...it'll be enough to tell if it's working or not.
  Different story if it's a damaged capacitor, has this board always had reverse polarity diode protection?
  Unplugged, start with DMM or audio probe at the input jack tip:
  It doesn't connect to ground, it does connect to a switch lug.
  Find the other lug on that switch it's now connected to [either the circuit board input wire or the bypass jumper], see what happens [what lugs make and break of input switch wire routing] when you hit the switch...when on the beep moded DMM lead at the jack tip should beep at the input capacitor, or at least it's wires board pad.
  Do the same deal with the output, jack tip not grounded, goes through switch to last circuit component.
  Does the battery clip large button connect to V+, small to ground pin 4?
  Do the battery clip +/- leads connect [you have power at the board so no, but always a good pre-power up test].
  power it up and use the audio probe on it.

[bigchasbroon]

yep i had 27pf on the input instead of 27nf (0.027uf) so i was x100 out. but the point i was trying to make is that i spent literally hours trying to figure it out replaced this and that and in the end when i used the audio probe i found the problem in minutes.

[jkokura]

I just triple checked - all my components are correct, all polarities are correct. I'm beginning to suspect there's a faulty cap or resistor, or even a transistor, but I don't know how to test that. Also, the voltages all seem to be correct from GGG's site, and if that's the case doesn't that mean that the parts are fine? Pete, I checked all the lugs on the switch - everything beeped loud and clear. It's not the switch. I've also beep tested all cabling. No breaks or hidden problems there (I use solid core sometimes, and sometimes that's the problem - not this time).

I guess I have to walk away from this for now. I might be able to find a local place that can sell me the stuff to make an audio probe, but I might have to figure out some other kind of solution out. Living in a smaller town sucks when even "the source" (formerly Radio Shack) doesn't have alligator clips, 0.1 or 1.0uf Caps, or even a replacement probe or jacks. Lame. Everyone keeps telling me that I need to be using an Audio Probe though, so I guess I gotta make that a priority. That should be a part of the Debugging page.

When I ordered from BYOC I had the choice between an audio probe kit and a confidence booster. I took the confidence booster.

I was kinda interested in this kind of Audio probe http://www.diystompboxes.com/smfforum/index.php?topic=78097.0 Perhaps I can get parts for that kind locally, but I'd need to know more details about how to build it.

Thanks guys for all the help and suggestions though. It's frustrating not being able to find the problem. I've been disciplining myself to fix this and another pedal before moving on to new things, and I think I have to move onto something new just to clear my head. Perhaps when I save up I'll get a new bigger enclosure and rehouse this and another pedal together - working with a new enclosure and a plastic DC jack might make it easier to see this with a clear head. Also an audio probe. Can't forget that.

I'll keep trying to make this work, but if anyone has a suggestion I'll be glad to hear it.