Crybaby wah problem

[Norgul]

Hello, i have a crybaby wah (rev g) that was modded to true bypass, and yesterday i wanted to add LED inside to be sure when it is on/off. Everything went well until I began drilling chasis. The inductor was obvieusly a bit old, and it just fell off. All my tries to restore it back were in vain (if that was the only problem anyway).

So what happens is, when connected and in off state, signal passes through, and I get the guitar tone on the amp, however, when it is on, everything is mute. I tried replacing the switch, didn't help. Is it possible for this kind of error to be caused by the inductor? Is there a way to check the pot with multimeter or something...

Also what I found a bit odd was that LED was giving light obviously in off state, since it was shining when i could get a guitar tone, and was off when everything was mute...maybe I connected it wrong. I use 9V adapter, without battery...could I have fried something?

Any help would be appreciated, thank you.

[GibsonGM]

Well, yeah, you could have fried something!  )

Maybe you could snap a shot of the board, the inductor and your switch wiring? <both sides please>

Lots of things could cause this...a disconnected switch wire, a short created when you tried to put the inductor back in.  A short to ground after the first transistor would silence it, and you were working in there...

Do you have, and know how to use, a multimeter?   If so, unplug power and look for continuity between + and -.   You'll have to 'short' the DC adapter with a jumper first.   How much you can diagnose depends on how comfortable you are with the meter etc.

[Norgul]

Thank you for quick response...here are pictures (if you can't see from these, i will try to get better photo equipment, this is just a mobile phone =/)

Upper side: that thing on diode and cap below the adapter input is just solder leftover, I didn't bother to remove it. The cap C9 is missing, it is the little yellow thing with barely readable sign, and i don't know which cap is it, so I can't buy a new one (the one which gets overriden for bypass mode).


Down side: those black marks on bottom are bad soldering from guy before, but those were there even before I started soldering, so it was working


The inductor is possibly faulty...I didn't know what to do, so I soldered 2 leads on it (since other two are redundant right?), but no luck. When I test it with multimeter with ohm settings on (I don't have inductance option), the needle doesn't even move, so I suppose the wire is cut somewhere?


And here is the switch. I resoldered it to original state (before I tampered it)


If you don't see it...
1 2 3
4 5 6
7 8 9


1 --> 8 link
2: blue
4: yellow (wire from capacitor, needed for bypass)
5: purple
7: black
8: green

Thank you very much

[GibsonGM]

Hi Norgul,

I came back in to tell you that when you test the power supply rails, + and -, for continuity, you can just do that right on the board.  Wife was talking to me before, so I made it more complicated than need be, ha ha.      You just want to make sure the power supply isn't shorted.   

Yes, it sounds like your inductor is shorted.   Now, I don't know about the 2 other leads, man.  Were all 4 soldered in?    My background is with old, 70's Thomas Organ Co. Crybabies, lol ;o) Only 2 leads, reads 56 ohms, and a slightly different schematic....   

What I'd do is see if any 2 have continuity.  If none do, then I think we can be pretty sure it's toast!    You can get one at the bottom, here:  http://www.smallbearelec.com/servlet/Categories?category=Transformers%2C+Inductors&searchpath=537056&start=9&total=28

Yeah, the pix are a bit fuzzy!  Good for a start, but I don't see anything obviously messed up.  You can also retrace all your wiring to be sure it's intact, not shorting against something...if you can shoot a clear pic of C9, we might be able to help...you mean, it's not in the circuit? If not, that could be an issue!

[Norgul]

Hello...I conducted some tests, and here is what I came up with:

- switch works (even the other one which I removed)
- pot works (checked with multimeter, it has variable resistance when I move the pedal up and down)
- input and output obviously work since signal is passing through
- I have rewired the inductor, and when connected to multimeter, it shows no resistance, so I guess there is no wire break anywhere, and it should work
- diode and resistors show values within specified parameters
- there is one 10nF cap missing (could that make everything not work?)
- I checked all 3 transistors, and 2 are good, but the third is showing value of 7 when checking first pair (PNp), and value of 18 when checking other (pNP)...should they be the same, is that malfunctioned transistor?
- the 220uF cap seems to be shorted when I put the multimeter on it, however, its resistance starts gradually increase (from 0 Ohms upwards)...is that okay?

Is there something else I can check...I'm a bit stuck here...

Thank you once again for your time

[PRR]

> inductor, ..., it shows no resistance

Inductor like this WILL have resistance. Perhaps 50 to 500 Ohms. It really must give a non-zero reading on a standard multi-meter. Otherwise you have somehow connected both legs to one end of the winding (and nothing on the other end).

> one 10nF cap missing (could that make everything not work?)

Parts aint free. Assume that every part is there for a reason. That's not always true (some designers are extravagant); and some parts only cover odd situations. But until you know why you don't need that part, probably good to put it in.

> the 220uF cap seems to be shorted when I put the multimeter on it, however, its resistance starts gradually increase (from 0 Ohms upwards)...is that okay?

A capacitor is a storage bucket. When it is empty current will go right in freely (low resistance). Eventually it fills-up and current stops (high resistance). 220uFd is a BIG capacitor relative to the current in a typical ohm-meter. Yes it should go near-zero and rise.

Also 220uFd is (probably) an Electrolytic. Which only blocks DC one way. If your ohm-meter polarity is opposite to the cap polarity, it will never "fill up" and show a low Ohms forever.

[GibsonGM]

Yeah...the main error I'd expect in an inductor would be INFINITE resistance, if it were burned open for some reason.  I probably wasn't clear on that, when I indicated above that it could be shorted rather than open.  And that you should read 50 or more ohms.  All good parts have SOME resistance, even if very small (like in a diode's forward direction)...it is how current is developed in a component, a physical property of a working device.

If you have everything back the way you think it should go (if the inductor is out again, re-test it and put it back in!), it's probably time to make an audio probe and find out where the signal dies.   Search in the forum if you don't know how to make one (everyone should have one).    Put ANY caps that fell out back in, lol!  PRR is giving good advice above this - everything in there is required!  That may be an input cap, and your signal may be stopping just before it, for instance....

No idea what a 'value of 7' is, relating to your transistors....please go to the beginning of the forum and read the "Debugging" thread, after you have it back together, and try to provide some voltages.  Then make yourself an audio probe.     

It's ok, you just need to go thru the process before you can do much that's meaningful to repair your wah!

[PRR]

> No idea what a 'value of 7' is, relating to your transistors....

Has me buffaloed also.

A *guess* is, since he wrote PNp and pNP, that he knows a transistor is two diodes, and is measuring diode conductance. But "7" what? Ohms? Mhos? Furlongs? And diodes being the loggy things they are, the number would cover a very specific condition, which isn't clear. Assuming the test is consistent, then "7" and "18" whatevers *could* mean a problem. Or not.

[GibsonGM]

> No idea what a 'value of 7' is, relating to your transistors....

Has me buffaloed also.

A *guess* is, since he wrote PNp and pNP, that he knows a transistor is two diodes, and is measuring diode conductance. But "7" what? Ohms? Mhos? Furlongs? And diodes being the loggy things they are, the number would cover a very specific condition, which isn't clear. Assuming the test is consistent, then "7" and "18" whatevers *could* mean a problem. Or not.

Well, I guess if the units are self-consistent, he may be on to something!!  Strange things can happen when you dig into a device, maybe you short something or break a wire or lead you can't see...maybe a cap falls out!!

Go here, Norgul, and try to get us the info requested, ok?  http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Gaining debugging skills comes with time and effort - give it a chance, try to follow the writeup, and we'll keep helping you. It's probably something simple...we just need to get on the same page with terminology, measurement and stuff...

[Norgul]

Sorry for the confusion, the thing is, I have no idea what did I measure on transistor, I was following a tutorial and so I have put my multimeter on the diode sign. On other two transistors, measurements were showing two similar values (emitter-base pair, and collector-base pair), however, I have no idea what units are those. I will check the link you have put here.

Anyway, I have also checked that connector that you plug in on the PCB (don't know what it is called), to check weather wires are okay, and everything is fine.
I have also rechecked inductor with digital multimeter (I have analog also, it seems it is not so good with low values), and it shows 30 Ohms, so its not short circuited.
And I have checked the adapter, it gives out the constant 9V, everything looks fine.

I ordered the little capacitor from the e-bay, don't know if there is some more reliable source for electronic components?

Thanks once again

[GibsonGM]

Small bear, affiliated with this forum, is a great place to find parts for our projects!  www.smallbearelec.com

Sounds like your inductor is ok.  Putting the capacitor back will be a big thing, I believe. 

You should learn more about your meter, Nogul.  I suggest using the DMM, mostly, yes.  Typically we will measure voltages and use the continuity function for our projects, if your meter has that capability too.    And when you measure a transistor in-circuit, you typically don't need the diode function....we just need you to power the effect up and carefully measure the DC voltage at each transistor pin. Don't short them with your probe!   You can put a jumper between your black (-) probe and a ground point, such at the - battery terminal or grounded sleeve of a jack, to do these measurements.     How they look in relation to each other can tell us what is happening inside the circuit.

https://learn.sparkfun.com/tutorials/how-to-use-a-multimeter

Look up "audio probe" on the forum, as well.  Making a simple probe will let you trace your way into a circuit and then (hopefully) find the point or stage at which things become distorted or whatever.   It can help pinpoint where your trouble is.

It's part of how you learn to do this. If you stick with it, you'll be able to debug your next problem on your own!  )

[Norgul]

Guess I have a lot of reading to do now, see you in a few days when I absorb it

[Norgul]

Okay, one thing isn't clear...I was measuring resistors once again, and several of them didn't show fixed variable...their resistance seemed to increase, is that normal?

[PRR]

Normal?

No. The ideal resistor is the same resistance ALWAYS. Practical resistors are non-ideal, but close enough for our practical purposes. There will be a few-percent drift for large chage of temperature, some deviation for very high (supersonic) frequency, etc; but all too small to easily show.

Are you reading naked resistors? Or resistors on a board with capacitors and transistors?

Are you holding the leads with your fingers? Your body has a resistance, and it changes, with finger-grip, sweat, and if you tell a lie.

[GibsonGM]

In other words - it's nearly impossible many times to read the value of a resistor (or cap, or other components) while IN the circuit.  Your meter gives out a small voltage that fills up nearby (connected) caps and throws you off constantly.      Transistors can have caps down the line, too, doing the same thing...you get it.....
 
You should never try to read resistance with the power "on" in a circuit.  Fast way to blow a meter fuse or burn out a coil.

So:  The only real meaningful readings you should try right now are voltage, with power on, of course.  Meter set to "DC Volts", "DCV" or the solid line with little dashes above it ;o)

You measure current with power on, too, but in a slightly different way that's not important to us right now.

[Norgul]

Hmm..as I was checking PCB for continuity, I noticed that the base of one transistor detached together with solder (on the green side of PCB). I will connect it to the next point with a wire, and see what happens. Also, I have ordered a new cap that is missing

[GibsonGM]

Yes, things like that would cause a 'degradation of signal', lol.   As in - causing NO signal.      How did all that happen? (the transistor + the cap falling out?).   

If you gently scrape and/or sand the PCB trace near where the pad lifted, you can create a point nearby to solder the transistor to.  Sometimes I'll put a very short piece of wire there, soldering to the trace end first, and let it solidify.   Then quickly tack the transistor to it.   You can bend the new wire into an "L" to hold it with small pliers while you tack it in, then cut the L off.  You must work FAST - transistors do NOT like too much heat!  Use a heatsink on it if you are able, if the leads are long enough.    So do the far end of the wire first so you don't have to mess around with the BJT too much...let us know how you make out.

[Norgul]

I can't believe it...it works! Transistor was the main problem (once I rewired the inductor).

But how it happened...the cap was holding loose, so i broke it unintentionally, however, chassis drilling might have caused the transistor to fall off...WARNING to everyone, don't be so stupid to drill the chassis while the PCB is inside

Thank you once again

[GibsonGM]

No problem, Norgul, glad it worked out!   You stuck to it until you found the problem.  Keep building, modding, and learning, and this stuff will get a lot easier!  )   

[PRR]

> don't be so stupid to drill the chassis while the PCB is inside

Not as dumb as drilling a wall with a telephone wire on the other side. A 104-pair cable for a busy office. I was splicing all night.