bad Phase 90...

[thejoe]

I was just given a Phase 90 from 1986 and it has a weird thumping sound when its on. Like its just phasing nothing. And then when you play you can still almost hear it. I'll find the time later to get at it with an audioprobe but does anyone think they can diagnosis it without search the entire circuit? I feel like its probably a pretty common thing..

Thank you,
Joe

[R.G.]

Bad Phase 90! No treat for you!

If the thumping follows the LFO, you have LFO voltage bleeding into the audio signal path.

Could be
(a) bad electro caps; I would personally just replace them all anyway.
(b) bad phasing JFET
(c ) board short/contamination

or some other things. Try those first.