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