Wah experts

[m-theory]

I'm repairing a Vox wah for a friend (not sure what year, but probably circa 1980's).  It came to me completely non-functioning. 

The first thing I found was that the wiring buss connector had come apart, so I plugged it back in.  That got me a "wah" tone, but no "whacka-whacka." 

I looked at the pot, and it was loose, and the wires were about to break off.  I stripped back the wires and re-soldered them, re-set the pot, and tried it again.  Same thing...wah tone, no whackity-whacka.

I checked the pot with my DVOM, and it sweeps from 1.5k to about 110k, so that appears to be functioning.  Just for giggles, I swapped the pot from my old crybaby, and that made no difference.

I found that the elec. cap was physically damaged, so I replaced it.  No change.

Now, it's beginning to irritate me.     I see nothing else on the thing that seems out of the ordinary...no broken wires, no broken or disturbed circuit traces, etc.  It seems as if the problem SHOULD be pot-related, since I get the "wah" tone, but no "whacka," yet the pot appears to be working. 

What am I missing?   

[jonathan perez]

there are too many variables in a wah to just say its the pot, especially with a "nonwahing" wah.

so!

change the battery (hey, you never know)

physically damaged electro? did it blow up? if so, put your meter across the caps, to see if it might have fried those too.

the inductor...see if theres any current going through, if not swap it for another. (your choice)

hmm...did you rewire it correctly?

[O]

I had a similar situation and it ended up being the inductor. The wire was broke just as it got wrapped around the soldering posts, so it was really hard to see.

[m-theory]

change the battery
I thought about this on the way to work this morning.  I did the "tongue check," and it bit, but didn't floor me, so it's not a full 9 volts.  I'll swap that just to eliminate that as a possibility.

physically damaged electro? did it blow up?
No.  The pedal is missing the two back screws, so the battery's been flying around in there, and appears to have gotten wedged against that cap at some point, and got maimed a bit.  It was probably still good, electronically speaking, but I didn't like the looks of it.  

the inductor...see if theres any current going through, if not swap it for another.
I'll check this, although since I have an open-wah sound, it would seem that the inductor is inducting.  

hmm...did you rewire it correctly?
The only thing I re-wired was the pot, and I just did one wire at a time.  

Any other thoughts?  I haven't put a meter to anything except the pot at this point, so that's where I'll have to go if the battery change doesn't get it going.  Anybody know what sort of numbers I should see at what points?  

[m-theory]

I had a similar situation and it ended up being the inductor. The wire was broke just as it got wrapped around the soldering posts, so it was really hard to see.
You had an open wah, but no "whacka-whacka" with this problem?  I would think that a broken wire at the inductor would result in no signal, due to a broken circuit.  I'm open to checking anything, however.  Like I said, it's beginning to piss me off.

[jonathan perez]

I'll check this, although since I have an open-wah sound, it would seem that the inductor is inducting.  

change the inductor and find out. 

[petemoore]

  I'm not completely certain this is a  'failure'...
  If it's justa basic wah, I've had them sound wah like, just no whakka, in fact hard to tell the treble from the bass side really.
    If it's kinda working, the wah pot movemtent should make 'some, at least slight difference when on treble to bass sides.
      Wah tone with limited 'whakka'...isn't that what most wahs do when new?
 Somewhere around here I've seen wah transistor voltages other wah voltages, the first transistor is a gain stage.
 I would just do the dogmatic, and test point w/DMM around in the circuit, it could be something like a lifted ground on a jack...typical stuff, test all grounds, measure resistors verify connections and non connections...
  I don't have it here to hear, but the symptoms seem maybe a bit like 'weak wah', as opposed to 'broke wah'.
  The inductor should read a really small resistance across the distant connections [R and continuity testing from 'distant' points also verifies the connections 'between']

[m-theory]

"If it's kinda working, the wah pot movemtent should make 'some, at least slight difference when on treble to bass sides."
There's absolutely no change in tone from one end of the pot to the other.

Wah tone with limited 'whakka'...isn't that what most wahs do when new?
Again, this thing does nothing except an open wah tone.  The "whacka whacka" isn't limited...it's non-existent.
   
I would just do the dogmatic, and test point w/DMM around in the circuit, it could be something like a lifted ground on a jack...typical stuff, test all grounds, measure resistors verify connections and non connections...

i'll do this.  I appreciate that input.

[powerplayj]

try the .01 sweep range cap.  I have 5 caps on a 6-position rotary and the empty terminal (6th position w/out a cap) on my switch sounds similar to your symptoms.

[m-theory]

The sweep range cap would be "C2," correct?
http://generalguitargadgets.com/diagrams/wah_847_lo_tb.gif

[m-theory]

Powerplay, I'd like your opinion on comparison between the BSIAB2 and the Thunderchief.  I've built several BSIAB2's for friends, and love that pedal (although I'm a tube-amp-distortion guy myself...I do admit that the BSIAB sounds pretty damned nice), but I'm really intrigued by the Thunderchief. 

[petemoore]

  yes, C2, the pot indexing [pinion gear position] also does treble/bass adjustment, I'd go for 'a range', before adjusting the range with that cap though.
 and I believe 'no wakka' ITCase means problem wah.
 Resistors you can measure, you've checked the pot.
 Electrolytic could have been reverse polarized, transistors too, perhaps I missed it, but I didn't see reverse polarity protection.
 That leaves the rest of the caps and connections...
 Connections can be tested, caps are down there on list because...the only way I test is with swaps, which requires...swapping, if they're non-polar and rated at say 16v or better, I don't see how reverse polarization of PS would damage them....still if the wah ain't werkin' and everything else tests out.

[Paul Marossy]

I would think that a broken wire at the inductor would result in no signal, due to a broken circuit. 

It'll still work with a broken inductor. It won't do much of anything, though - it doesn't even behave like a volume pedal. But, it does pass a signal just fine.

[jonathan perez]

I would think that a broken wire at the inductor would result in no signal, due to a broken circuit. 

It'll still work with a broken inductor. It won't do much of anything, though - it doesn't even behave like a volume pedal. But, it does pass a signal just fine.

which is why i believe its the inductor. 

[MikeH]

+1 on the broken inductor.  I just fixed a Cry Baby that had that problem.  Some of those stock inductors have such tiny wire in them and they're ridiculously delicate.  If you put any kind of pressure on them, the contacts snap.

[GibsonGM]

hey, if a trace to the inductor broke, or it shorted and failed, couldn't backcurrent from the collapsing field have flooded thru that cap and toasted it?  Just a thought - I'd look at the inductor, too.  After I'd sort of followed some voltages & played with the pot all the way thru rotation by hand...

[Paul Marossy]

hey, if a trace to the inductor broke, or it shorted and failed, couldn't backcurrent from the collapsing field have flooded thru that cap and toasted it?

In my book, highly doubtful since we are only using a 9V battery.

[m-theory]

***UPDATE***
PROBLEM SOLVED!!!


As usual, it turned out to be something incredibly simple.  The ground wire from the pot had broken crisp and clean right at the output jack.  Initial appearance was that it was connected, but it was not.  A quick re-strip and resolder, and the pedal works perfectly! 

I'm still not real impressed with the look of the pot (it appears to be seeping oil), so I let the guy know that it may not last long.  He may end up having me replacing that if/when he brings it back for a true bypass mod. 

Anyway, to recap, I initially found a disconnected wiring harness, then replaced an elec. cap that had become physically damaged, then found the pot to be loose and wires there to be very near breaking off, and finally, the real culprit, this broken ground wire.  What should've been a very simple repair ended up being much more, simply because the actual problem was so well hidden.  The other things had to be repaired anyway, however, so it's no loss. 

I thank you all for your input!