Digitech DF-7 Distortion Factory issue

[runmikeyrun]

Hey everyone,

I picked up a Digitech DF-7 Distortion Factory off ebay, broken of course.  The indicator light stays on all the time, yet the pedal is in bypass mode.  My first instinct was the switch, but it's good.  I even removed it and tried shorting the terminals.  I'm thinking there's an issue in the switching circuitry, but I don't have a schematic and digitech said they don't provide schematics for current production pedals.

I've tapped around pretty good inside there.  Sometimes there's a hiss coming through, and it can be made worse when I move around the battery wires or touch a cap here and there, but it's never the same part twice that seems to cause it.

One thing that seems weird- the filter cap (330uF) has 0v at ground, but only 1.3v on the + side.  That seems weird to me.  I do have 9v at the power jack.  I checked the polarity diode and it seems good, but both diodes in the pedal read 0v no matter which way I test the diode.  Idk, maybe my tester is screwed up.  There are no markings on the diode of course, so what would be a suitable replacement?

Thanks everyone.  Obviously if anyone has a schematic sharing would be much appreciated.

Thanks,
Mike

[segaura]

I am aware I am writing under a more-than-ten-years-ago post.

I am really interested in knowing if there has been any advancement in this troubeshooting.

I recently started working on a faulty unit which shows exactly the same behaviour, led starts on and stays on regardless of everything else.
One single day, while testing, the unit correctly worked, but never since then.
I removed most of the caps to test them outside of the circuit, ESRs were not great but they are in working condition so I mounted them again.
Injecting a sine wave and following the signal path with oscilloscope probe resulted in finding it on many via/component side, initially identical to the input one, later phase-reversed.
Having seen this signal in many places made me think there were no issue on power supply input stages, so I have not already checked 330uF cap and surrounding maybe-diodes, I'll do.
The routing around the PCB is hard to understand, especially for traces laid out under the jack connectors.
Additionally main IC has so small pins that I have not tried already to look if the signal is reaching one of them.

[garcho]

Removing all the caps is something you might do to a classic (read: old) piece of studio gear you're rehabbing, it's not something you should do as a standard troubleshooting first step.

The 330u cap is there to iron out power supply ripple. The diodes are for polarity protection. If you're getting PS voltage on op amp PS pins, the PS is fine.

The main IC is a tiny computer that does all the work. It's not repairable or replaceable. You can fry them out poking around if you're not careful.

And...

WELCOME TO THE FORUM!