DigiTech Whammy Pedal Checkout

This pedal wouldn’t work regardless of how it was connected. He tried the supplied power supply and a pedal power unit in his pedal board, with no luck.  Could the Unbrokenstring Crew straighten out this mess?

We put the pedal and the power unit (wall wart) on the bench and verified that nothing worked.

Here is the clue.  The customer provided a DC 9v output wall wart, a power standard which is commonly used in the world of guitar effects pedals.  That power standard is not compatible with this unit.

Not much else to see around the rest of the pedal.  The MIDI control is a nice touch.

This is the ‘correct’ wall wart.  This one says 9vac output, which is what this pedal needs.  I love eBay!

Something is rattling inside this unit.  Removing these Allen head cap screws will allow us to open the case.

This is what is rattling.

And here is where it goes.  This hardware works well, so we can set the switch aside for now.

The electrical connection between the circuit board ground and the chassis is made via this metal stand-off.  This connection was intermittent until we took the wire brush to the end of the stand-off.

The light spot on this circuit board is called ‘measling.’  This indicates that something got very hot.

This inductor goes between the power supply and the chassis ground of something plugged into the pedal.  So, it failed.  The head of the destruction caused the measling seen above.

Here is another view.  This inductor serves as a simple noise filter when nothing is plugged into the guitar input jack.

The inductor is replaced and the unit goes back together.  Working with the correct wall wart, this pedal is fun!  It does pitch bending and chorus effects surprisingly well, considering its age and the technology used.

Thanks for reading all the way through!

CONTACT – David Latchaw EE
281-636-8626

Ibanez TubeScreamer Pedal Repair

Steve said that his Keeley-modded Tube Screamer pedal had quit.  Could the Unbrokenstring Crew bring it back to life?

This pedal is in great shape cosmetically!

Robert Keeley made a few circuit changes that are well-documented on the Web.  This pedal has those changes.

The battery box has its own lid.

The bottom of the pedal is shielded with the metal screen seen in the center.

A die cut sheet of black insulative material protects the circuit board from the metal shield.

Let’s get it all out of the enclosure so that we can work on it.

We’ve applied battery power and connected up to my Marshall Stack.  The original problem is still with us.

An oscilloscope probe verifies that the dual operational amplifier is defective.  Part of the Keeley mod specifies a Texas Instruments 4558 dual op amp.  This IC is socketed, so replacing it is trivial.

Here is an example of the softly clipped audio that the Tube Screamer delivers to the amp input.

Reversing the disassembly procedure is all we need to do to get this cool little pedal back together again.  We’re done.

Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Boosta-Grande Pedal Repair

We did a quick-and-easy foot switch repair on this gain pedal.  Here’s the scoop:

The operation of this pedal was intermittent.  The switch didn’t click anymore.  Yup.  Probably just needs a foot switch.

 

The foot switch is on its own circuit board.  This switch is a latching, 3 pole double throw unit.  A ribbon cable carries all the lines between the terminals of the switch and the rest of the electronics.

 

The circuit board was carefully de-soldered using braid wick and lots of flux.  We’re ready for the new switch.

 

Here is the switch…  or what’s left of it.  The pedal enclosure was holding everything together.

 

The new switch was installed so that a minimum amount of threads were exposed on the top side.

 

The switch was adjusted so that the terminals on the switch lined up with the slots in the circuit board.

 

Everything lines up where it should.  See, I said that this would be easy!

 

The chef ordered new solder fillets all around!

 

An easy fix, and this boost pedal is VERY clean.  We’re done here!

Thanks for reading!

CONTACT – David Latchaw  EE
281-636-8626