Dunlop MC404 CAE Wah Pedal - No Power Help

[misterc57]

This pedal has no power on the board. I have not been able to find a schematic. If anyone has a schematic for this, or a similar model that could help, please post it.

I see 9V on the board from the battery to the AC adapter port pins. After that I only see around 3V on the board, example at the filter caps, the switch pins, and the TL032CP chip.

A soon as insert a phono plug into the instrument jack, I see no measurable DC anywhere.

The pedal has LEDs that should light up. They do not under any scenario.

Can anyone assist?

Thank you folks! MarkO

[Jon Snell]

Phono plug? These use jack plugs, not phono.
Battery or power supply ... what are you using?
Wrong polarity power supply may cause that.
Check the DC socket contacts.

[Helmholtz]

OP probably means phone plug not phono plug. https://en.wikipedia.org/wiki/Phone_connector_(audio)

[misterc57]

Phono plug? These use jack plugs, not phono.
Battery or power supply ... what are you using?
Wrong polarity power supply may cause that.
Check the DC socket contacts.

Yes 1/4" phone plug. Sorry.
I am using a 9V battery plugged into the pedals battery clip.
DC sockets seem clean/okay and I am seeing continuity to the board pins.

Seeing 3.4 VDC at adapter pin which drops to 0 VDC when plug is inserted to instrument input jack.

[g1]

Use input jack ground for your black probe, with a mono plug in it. Check DC on all 3 of those DC jack pins.

[misterc57]

Use input jack ground for your black probe, with a mono plug in it. Check DC on all 3 of those DC jack pins.

I am seeing the same results, 9v, 9v, 0v

[Helmholtz]

Is you battery fresh?
Did you also try a suitable 9VDC power supply?

Though not very likely it might be necessary to mount the board to the shell for ground continuity.

My first suspect would be a bad D4, assuming it's used as protection diode. Also verify R16.

Without a schematic you should try to trace out the power supply input wiring.

[Mick Bailey]

You could try tacking a spare battery connector directly to the board to power it. If that works then perhaps it's a connection/socket/wiring issue. What you're reading may be a ghost voltage - a voltage that disappears because of very high series resistance somewhere and any kind of loading pulls it down to close to zero. A check for this is to clip-lead a resistor across your meter probes to artificially reduce the meter impedance to load the circuit and re-measure the voltage. Try 10 kΩ.

[misterc57]

I saw the same results when the board was originally mounted inside the pedal.

Using a new battery. My 9 V readings are actually 9.6 V

Wiring from battery to board is good and making it to the DC plug adapter.

D4 and R16 (100 ohm) tested good in circuit. I see no V at either component under any scenario.

Tried a 9V Boss DC plug adapter. I see 9V at adapter pin when plug inserted into instrument jack but no V on board anywhere else.

[Helmholtz]

Not sure, but I think I've seen a wah pedal that required a plug in the OUTPUT jack (as opposed to normal instrument input) to engage power.

[misterc57]

Update. I am placing the - probe on the DC adapter ring and the + probe on components.

I now see -9.3 V at D4 and R16. A .3V drop across D4. and at the TL032 chip

LEDs still do not light up.

[Helmholtz]

Not clear.
What voltage do you measure with red probe to TL032 pin 8 and black probe to TL032 pin 4?
https://www.ti.com/lit/ds/symlink/tl...oogle.com%252F

[misterc57]

Not clear.
What voltage do you measure with red probe to TL032 pin 8 and black probe to TL032 pin 4?
https://www.ti.com/lit/ds/symlink/tl...oogle.com%252F

I did not word that well. Meant to say there is power on the board and a drop across the diode. LEDs still do not light up. Issue is no signal to amp when activated. Passes signal when switched off.

TL032 seeing 0.8 mV with red probe to TL032 pin 8 and black probe to TL032 pin 4

[misterc57]

I am getting confused on how to read V on this board. I get different results based on where I place the black probe.

The screw holes that attach the board to the pedal body have continuity to the input jack ground, so I would think I can use that. I see 0.3 V at D4 (no plug inserted at input jack), then 315 mV with the plug inserted.

[Helmholtz]

Use Ohmmeter to measure resistance (no battery, no power supply, phone plug inserted)

- from battery clip minus to TL032 pin 4,
- from battery clip plus to TL032 pin 8,
- from battery clip plus to clip minus,
- from TL032 pin 4 to pin 8.