Tube Screamer acting up after having it for a while.... :(

[studiostud]

Hi everyone,

As if there weren't enough topics out there for Tube Screamers, I am unfortunately bringing one more to the table.  I built a TS-808 from the tonepad schem about a year and a half ago and have been using it with great results ever since.  About a month ago, it all of a sudden stopped working.  I tested it with an audio probe and multimeter and traced the problem to a blown 4558.  I swapped it out and, bam, worked great.  Then I used it at a gig that night and after about an 45 min of solid use, it stopped working again.  Brought it home... tested... blown 4558.  What could have happened that would cause this, especially since it's worked great for over year?

Any ideas?

Jeff

[earthtonesaudio]

Sounds to me like power supply problems.  Did this happen with a battery or with an adapter?
If it happened with a battery, the next place I'd look is for shorted caps or protection diodes.

[studiostud]

I think it did happen with a power supply.  I've used that power supply with other things too though, both before and after the incidents, with no problem.  Which diodes are the protection diodes?

[earthtonesaudio]

Probably one diode is used for protection right near where the power comes in.  Cathode to +, anode to ground.
Another possibility is that the power supply let through some sort of fast, high voltage transient.

[studiostud]

The only diodes I can see are for the clipping stage of the circuit.  The +9v input on the PCB goes straight to the trannys and Pin 8 on the IC.