Old CryBaby wah pedal nnot "wah-ing"

[Fred G.]

The switch is working fine. The pedal provides a good, strong signal whether engaged or not. I've taken out screw #2 as per the photo immediately above. The circuit board will not lift out. It appease to be hung up on the bottom of the bolt at the bottom right corner of the inductor in the photo above. This bolt is one of two bolts holding down a metal "strap" which appears to assist in mounting the treadle to the base of the pedal.

As far as I can tell (difficult to see clearly due to space), there appears to be a nut glued to the underside of the circuit board that this bolt is screwed into, and this has locked down the circuit board. There also appears to be a thin layer of a clear glue holding down the base of the inductor.

I'll test these components as suggested and report back. Thanks!

[Helmholtz]

What a mess!
If you actually need to remove the treadle start with removing the hex nut just above the battery.

[vintagekiki]

In the previous post I forgot to mention ...
in addition to unscrew the metal screw (2) scrape off the glue (varnish) from the metal Wedge Pin (3)
The PCB is removed vertically.

[Fred G.]

THAT is the problem component. But that "wedge Pin" is actually the bottom end of a bolt holding down one end of that metal "strap" I keep talking about. It appears to be driven through a nut that may or may not be glued to the circuit board. When I wiggle the circuit board, I can see the bolt (just under the front of the treadle) move along with the board. I found a dental mirror I'd forgotten that I have; maybe I can get a clearer view of what's going on with that.

[52 Bill]

Is the circuit working in both modes without the battery connected? If the pedal is turned on, there normally is a noticeable treble boost to the guitar signal.

Please do not even think about removing the treadle to get the board out. You will only spend a lot of time and energy that you don't need to spend. Once the mounting screw has been removed, try slightly twisting or jiggling the board to break what could be some sort of glue that is keeping the board in place.

To answer an earlier comment on one of my posts, here is my uneducated take on the circuit.

There are two stages to the basic Vox/Cry Baby circuit. The first basically is an inverting stage with an LRC filter at the input. The filter removes a band of mid and low frequencies from the input signal.
The second stage is a non-inverting stage that is controlled by the treadle pot. When the treadle is toe-down, the signal into the second stage is grounded, so we hear only the treble boosted sound. The output of this stage is fed back into the input of the first stage via a 0.01uF cap. This signal is out of phase signal with the input signal, so when the two signal are mixed, there is a cancellation of the upper frequencies that cause the tone of the signal to lower or sweep through the filter range and create the wah sound.

So if the signal through the first stage only is not treble boosted, then there is a problem with the filter section. If the treble boost is there and there is no wah effect, then problem lies in the pot and or second stage of the circuit.

Good luck with the repair.

[vintagekiki]

Scrape (remove) the glue from the "wedge pin", desolder the short green wire from the jack (left) and carefully pull the PCB vertically upwards.
The PCB is difficult to separate from the wah chassis, because the tight hole of the PCB through which the "wedge pin" passes.

[Helmholtz]

There are two stages to the basic Vox/Cry Baby circuit. The first basically is an inverting stage with an LRC filter at the input. The filter removes a band of mid and low frequencies from the input signal.
The second stage is a non-inverting stage that is controlled by the treadle pot. When the treadle is toe-down, the signal into the second stage is grounded, so we hear only the treble boosted sound. The output of this stage is fed back into the input of the first stage via a 0.01uF cap. This signal is out of phase signal with the input signal, so when the two signal are mixed, there is a cancellation of the upper frequencies that cause the tone of the signal to lower or sweep through the filter range and create the wah sound.

The principle is somewhat different (see also R.G. Keen's article on Geofex).
The first stage is a common emitter amplifier with a voltage gain of around 27 and an LCR filter (parallel resonant filter) at its input as you said. Together with the 68k input series resistor this constitutes a frequency dependent voltage divider with a resonant peak. But the C of the filter (10nF) is not wired to ground but in the NFB path from the second stage (emitter follower). This kind of wiring results in a capacitance multiplier circuit using the Miller effect. The effective filter capacitance depends on the open loop gain between the cap's ends. The gain is varied by the pot, so the capacitance and resonant frequency vary with pot setting.
So we have a tuneable resonant filter.

[g1]

Pictures of the actual unit would be really helpful here as far as the board removal goes.

[Helmholtz]

Pictures of the actual unit would be really helpful here as far as the board removal goes.

See post #16.

[g1]

Thanks Helmholtz.
It looks to me like that strap bolt has self-tapped itself into the circuit board. Trying to pry the board off might crack it. I think the bolt head will have to be turned counter-clockwise till the board is pushed off (un-threaded).
Fred G. I think if you try undoing the bolt at the strap end, the nut will probably stay on and the board will be freed. (the nut is probably glued to the bolt)

[vintagekiki]

https://www.electrosmash.com/vox-v847-analysis
<sub>Vox V847 Wah-Wah Analysis


The Vox V847 Circuit Bias</sub>

For removal wah PCB scrape (remove) the glue from the "wedge pin"
https://images.reverb.com/image/upload/s--q6No-dwW--/f_auto,t_large/v1574631407/p7voxkmutupvctit35mk.jpg
https://images.reverb.com/image/upload/s--YFSZh6od--/f_auto,t_large/v1556658790/sfognznhbl6yfugmrvqn.jpg
https://i.imgur.com/4qGcipK.jpg
Wah PCB "Under the Hood"

1)
https://music-electronics-forum.com/forum/effectification/guitar-effects/37808-
Italian Jen Cry Baby - Drop in Volume and Bass when engaged

[Fred G.]

Welp, a couple of things...first, let me say I haven't looked at the links provided above yet, buy I will in just a minute.

Measuring across the 33k resistor connected to the inductor yielded a value of 30k, within 10% tolerance. This would indicate the inductor is bad?

And looking under the circuit board with a dental mirror, I see a nut that appears to be cemented to the board, looks like a thick pad of a white-ish adhesive between the nut and board. That is what the "treadle strap front bolt" is driven through. Scraping adhesive off the protruding end of the bolt ain't gonna get me there, apparently. Man, what a nightmare for such a simple circuit!

I checked out the link - the photos will be very helpful when I can get the circuit board out - but - how in the hell am I gonna do this without taking off the treadle? I'm stumped by the simple physicality of this pedal's assembly - I don't see how it could have humanly been possible without specialty tools.

[Helmholtz]

Measuring across the 33k resistor connected to the inductor yielded a value of 30k, within 10% tolerance. This would indicate the inductor is bad?

Looks like an open inductor. Should measure around 36R.
It might be possible to repair it by resoldering the coil wires connecting to the 2 pins accessible from the top.
That inductor is definitely worth repairing.

[vintagekiki]

This inductor is definitely worth repairing.

This requires removing the PCB from the wah chassis, remove inductor, reparing inductor ...

And looking under the circuit board with a dental mirror, I see a nut that appears to be cemented to the board, looks like a thick pad of a white-ish adhesive between the nut and board.

Fred G. please photo the bolt (screw) in close-up. To remove glue fom the bolt, try to carefully heat the bolt with a strong soldering iron to melt the glue.
The nut you see most likely holds a bolt attached to the wah chassis. White-ish adhesive on the nut, prevents the nut from loosening.

[Fred G.]

Fred G. please photo the bolt (screw) in close-up. To remove glue fom the bolt, try to carefully heat the bolt with a strong soldering iron to melt the glue.
The nut you see most likely holds a bolt attached to the wah chassis. White-ish adhesive on the nut, prevents the nut from loosening.

That is exactly what I have been describing for three pages now. The bolt cannot be accessed to unscrew it. The nut cannot be accessed to turn it. It is cemented to the bottom of the board. The access is so constrained that tools cannot be inserted to do anything. THAT is the problem, and, yes, as I have said repeatedly, the nut holds a bolt coming through the wah chassis (I've referred to it as the "front treadle strap bolt"), and it can't be accessed without removing the treadle, as far as I can tell. I'm trying to find a solution to that, I sure as hell can't visualize one. I can try super-heating the bolt and see if it melts the adhesive, otherwise, the treadle has to come off, or - this pedal will make a nice bookend. It's driving me mad with frustration!

Thanks!